Disc Brake Hold Off & Prop Valves

[AJ/FormS]

Um........ adjust the carb?
Your carb has 4 or 5 major fuel delivery circuits; so you need to be a lil more specific as to under what circumstances it is lean.
Your carb is a speed/density device. It reacts to rpm and load.
If it's running lean, that means it's moving air, which is a good thing. Your job is to make sure as best as you can, to make sure that air has the right amount of fuel in it.
The circuits are;
the Low-Speed, which is the Idle and Transfer Slots
the WOT (Wide Open Throttle), which is the MJs together with the PV (PowerValve or Power System)
the Part Throttle, which is principally the Primary MJ.
It is important to remember that as the throttle is opened, and each subsequent system comes on line, NONE of the other systems actually shut off. This means that as your rpm is screaming thru the Torque peak at WOT, the idle system and the transferSlots are still supplying some fuel, together with the Mainjets and the Power System.
On Holley-type carbs the Idle Circuit is comprised of FIVE parts, namely;
the Fuel level, the Idle-air bleeds, the low-speed circuit, and the mixture screws together with a small amount coming from the transfer slots.
The hardest system to adjust right, is this Idle-System, so let's start there.
If your engine seems to be lean at idle, and you are experiencing a tip-in sag or hesitation; I can almost guarantee you that your transfers are NOT flowing enough or Not flowing at all. If this is true, I can almost guarantee you that you are running too much Idle spark-advance.
While it's true that the 292 cam likes a lot of spark-advance, it is JUST as true that the 318 cam likes lots of spark advance. The problem is that with increased IDLE spark-advance, comes increased Idle-rpm. Which causes you to to close the throttle, but that action simultaneously shuts off BOTH air and fuel. So you can only reduce the throttle so far and then the transfer slots get shut off. You can make the engine still idle, by opening the mixture screws but eventually they top out at max flow. But you can make it idle this way.
But two things happen when the Idle is fudged up this way;
1) almost invariably the transfers stop flowing, so when you step on the gas at idle, it takes a bit of time for the circuit to come back on line, during which the AFR goes horribly lean, and then you get a lean tip-in stumble. and
2) as soon as you get past the stumble, the AFR goes very rich because the mixture screws are wound out all the way.
And the reason for this monkey-business is the excessive Idle spark-advance.

The increased spark advance is sometimes/ usually nice to have because the very low-rpm power goes up, making the engine both more responsive and peppier and that makes it more fun to drive. But getting off-idle advance by cranking the Idle-advance up, is NOT the answer.

So, if you have done this, you gotta undo it.
Start here;
remove the carb and set the transfer slot exposure underneath the Primary throttle blades to a little taller than wide; enough so that you can just see it. Reset the mixture screws to, in the center of their working range, which on a Holley type is no more than one turn out from lightly seated. I think all metering-rod carbs are about 2.5 turns out. CLOSE the Secondaries up tight but not sticking.
Make sure your Vcan is connected to a ported vacuum source, for now.
Make sure you have a PCV installed and plumbed correctly which is to the underside of the primary throttle blades.
Make sure your brake-Booster is dead-headed at the diaphragm, that is to say, not sucking air continuously.
Make sure that the intake is sealed to the intake ports.
Make sure that the carb is sealed to the pad.
Make sure that ALL vacuum devices that may be bolted to the intake, are functioning as designed.
Make sure your exhaust is flowing freely. I assume that you have headers, cuz that cam demands them. And it also demands the heat-crossover be defeated *1
Make sure your valve lash, if any, is on the loose side. *2
Make sure that if you are running Hydraulic lifters, that the preload is on or close to the minimum adjustment.*2
Make sure your ring gaps are adequate, that the rings don't drag your idle-speed down as the engine comes up to temp.*3
Make sure your engine temp is at least 180* and is stable.*4
As always, make sure your WET fuel-level is constant.
Ok then;
Bolt the carb back on and start her up. you will immediately notice the higher idle-speed; do not touch the Curb-Idle speed screw! After she warms up, back off the timing to get the rpm that you want. This is your starting point. From here you need to fine tune it just a lil for your particular combination of parts.

Each of the circuits have different ways to be adjusted. On some circuits the air can be trimmed as well as the fuel.
At WOT, you need to adjust the mainjets
At Idle, the transfer slots to idle circuit balance, and trimmed by the mixture screws.
At Part Throttle, mostly the Primary MJ, but includes the PV opening point .
But no matter what you do, the very FIRST adjustment is always the Fuel Level.

Happy HotRodding.

*1 If you don't block the cross over, then during the end of the exhaust cycle, with headers, when the negative exhaust pulse is supposed to be helping the exhaust out and the new fresh A/F charge into the cylinder, the signal gets lost in the passage and out the other side. This happens to the center FOUR cylinders. This robes your engine of a lot of power potential. I'll guess a full cam size worth of power.
*2, if the valves do not seat properly; firstly, they run hot, but secondly max cylinder pressure is not achieved, and thirdly, the overlap period gets screwed up. Loose is better than tight, but hydraulics should Not be clacking.
*3 tight rings put a tremendous amount of heat into the cylinder walls but also require a lot of horsepower to drag up and down. Too tight and they can tear the tops of the pistons right off.
*4, DO NOT BOTHER trying to tune an engine in the which the idle coolant temperature is all over the place. If it varies more than 10* fix it! The thermostat sets the MINIMUM coolant temperature, and that is all it does or should I say, that is all it is supposed to do,lol. If you have alloy heads, I suggest trying to run them a lil hotter; I have been running mine at 207* since 1999. Alloy heads suck heat out of the chambers very well, to the point that your engine needs the equivalent of about a half to a full point more Static Compression Ratio just to break even (to iron heads) on the Power Delivery. Whereas with iron, your pressure is limited to about 160/165psi for use with pumpgas, you can run at least 20/25psi more with Alloy heads, and you sorta need to, to compensate for the loss of chamber heat at WOT.

 

[D.Coulter]

Um........ adjust the carb?
Your carb has 4 or 5 major fuel delivery circuits; so you need to be a lil more specific as to under what circumstances it is lean.
Your carb is a speed/density device. It reacts to rpm and load.
If it's running lean, that means it's moving air, which is a good thing. Your job is to make sure as best as you can, to make sure that air has the right amount of fuel in it.
The circuits are;
the Low-Speed, which is the Idle and Transfer Slots
the WOT (Wide Open Throttle), which is the MJs together with the PV (PowerValve or Power System)
the Part Throttle, which is principally the Primary MJ.
It is important to remember that as the throttle is opened, and each subsequent system comes on line, NONE of the other systems actually shut off. This means that as your rpm is screaming thru the Torque peak at WOT, the idle system and the transferSlots are still supplying some fuel, together with the Mainjets and the Power System.
On Holley-type carbs the Idle Circuit is comprised of FIVE parts, namely;
the Fuel level, the Idle-air bleeds, the low-speed circuit, and the mixture screws together with a small amount coming from the transfer slots.
The hardest system to adjust right, is this Idle-System, so let's start there.
If your engine seems to be lean at idle, and you are experiencing a tip-in sag or hesitation; I can almost guarantee you that your transfers are NOT flowing enough or Not flowing at all. If this is true, I can almost guarantee you that you are running too much Idle spark-advance.
While it's true that the 292 cam likes a lot of spark-advance, it is JUST as true that the 318 cam likes lots of spark advance. The problem is that with increased IDLE spark-advance, comes increased Idle-rpm. Which causes you to to close the throttle, but that action simultaneously shuts off BOTH air and fuel. So you can only reduce the throttle so far and then the transfer slots get shut off. You can make the engine still idle, by opening the mixture screws but eventually they top out at max flow. But you can make it idle this way.
But two things happen when the Idle is fudged up this way;
1) almost invariably the transfers stop flowing, so when you step on the gas at idle, it takes a bit of time for the circuit to come back on line, during which the AFR goes horribly lean, and then you get a lean tip-in stumble. and
2) as soon as you get past the stumble, the AFR goes very rich because the mixture screws are wound out all the way.
And the reason for this monkey-business is the excessive Idle spark-advance.

The increased spark advance is sometimes/ usually nice to have because the very low-rpm power goes up, making the engine both more responsive and peppier and that makes it more fun to drive. But getting off-idle advance by cranking the Idle-advance up, is NOT the answer.

So, if you have done this, you gotta undo it.
Start here;
remove the carb and set the transfer slot exposure underneath the Primary throttle blades to a little taller than wide; enough so that you can just see it. Reset the mixture screws to, in the center of their working range, which on a Holley type is no more than one turn out from lightly seated. I think all metering-rod carbs are about 2.5 turns out. CLOSE the Secondaries up tight but not sticking.
Make sure your Vcan is connected to a ported vacuum source, for now.
Make sure you have a PCV installed and plumbed correctly which is to the underside of the primary throttle blades.
Make sure your brake-Booster is dead-headed at the diaphragm, that is to say, not sucking air continuously.
Make sure that the intake is sealed to the intake ports.
Make sure that the carb is sealed to the pad.
Make sure that ALL vacuum devices that may be bolted to the intake, are functioning as designed.
Make sure your exhaust is flowing freely. I assume that you have headers, cuz that cam demands them. And it also demands the heat-crossover be defeated *1
Make sure your valve lash, if any, is on the loose side. *2
Make sure that if you are running Hydraulic lifters, that the preload is on or close to the minimum adjustment.*2
Make sure your ring gaps are adequate, that the rings don't drag your idle-speed down as the engine comes up to temp.*3
Make sure your engine temp is at least 180* and is stable.*4
As always, make sure your WET fuel-level is constant.
Ok then;
Bolt the carb back on and start her up. you will immediately notice the higher idle-speed; do not touch the Curb-Idle speed screw! After she warms up, back off the timing to get the rpm that you want. This is your starting point. From here you need to fine tune it just a lil for your particular combination of parts.

Each of the circuits have different ways to be adjusted. On some circuits the air can be trimmed as well as the fuel.
At WOT, you need to adjust the mainjets
At Idle, the transfer slots to idle circuit balance, and trimmed by the mixture screws.
At Part Throttle, mostly the Primary MJ, but includes the PV opening point .
But no matter what you do, the very FIRST adjustment is always the Fuel Level.

Happy HotRodding.

*1 If you don't block the cross over, then during the end of the exhaust cycle, with headers, when the negative exhaust pulse is supposed to be helping the exhaust out and the new fresh A/F charge into the cylinder, the signal gets lost in the passage and out the other side. This happens to the center FOUR cylinders. This robes your engine of a lot of power potential. I'll guess a full cam size worth of power.
*2, if the valves do not seat properly; firstly, they run hot, but secondly max cylinder pressure is not achieved, and thirdly, the overlap period gets screwed up. Loose is better than tight, but hydraulics should Not be clacking.
*3 tight rings put a tremendous amount of heat into the cylinder walls but also require a lot of horsepower to drag up and down. Too tight and they can tear the tops of the pistons right off.
*4, DO NOT BOTHER trying to tune an engine in the which the idle coolant temperature is all over the place. If it varies more than 10* fix it! The thermostat sets the MINIMUM coolant temperature, and that is all it does or should I say, that is all it is supposed to do,lol. If you have alloy heads, I suggest trying to run them a lil hotter; I have been running mine at 207* since 1999. Alloy heads suck heat out of the chambers very well, to the point that your engine needs the equivalent of about a half to a full point more Static Compression Ratio just to break even (to iron heads) on the Power Delivery. Whereas with iron, your pressure is limited to about 160/165psi for use with pumpgas, you can run at least 20/25psi more with Alloy heads, and you sorta need to, to compensate for the loss of chamber heat at WOT.

 

[D.Coulter]

Good evening AJ,
Just a little about the car. It's a 67 barracuda notch back, I owned this car for 35 years. So, it's has a 71" 340 w/kieth black pistons, 508 292 with tti headers. Iron heads ported/polished. Manual breaks/steering, hydraulic lifters with roller rockers. QF dp 750 black diamond, no VS. Full MSD ignition. Set at 32 degrees advance @2000 rpm. Full tub w/cage, 4 wheel disc break. It's a complete street car. Ok with that said I'm having issues with it running rich. This carb is kicking my butt. Do you think the carb is to much for that engine, should I consider a 680. I have adjusted the transfer slot, bigger Air Bleeds and power valve. It's a 4.5 was a 6

 

[D.Coulter]

Good evening AJ,
Just a little about the car. It's a 67 barracuda notch back, I owned this car for 35 years. So, it's has a 71" 340 w/kieth black pistons, 508 292 with tti headers. Iron heads ported/polished. Manual breaks/steering, hydraulic lifters with roller rockers. QF dp 750 black diamond, no VS. Full MSD ignition. Set at 32 degrees advance @2000 rpm. Full tub w/cage, 4 wheel disc break. It's a complete street car. Ok with that said I'm having issues with it running rich. This carb is kicking my butt. Do you think the carb is to much for that engine, should I consider a 680. I have adjusted the transfer slot, bigger Air Bleeds and power valve. It's a 4.5 was a 6

 

[AJ/FormS]

Do you think the carb is to much for that engine

A 750 is absosoeffinglutely not too big, for that combo. lol.

You still haven't said when and where under what circumstances it is rich, and how you know this.
What gears and stall are you running?

 

[D.Coulter]

A 750 is absosoeffinglutely not too big, for that combo. lol.

You still haven't said when and where under what circumstances it is rich, and how you know this.
What gears and stall are you running?

Good Morning,
This is a recent build and I have not even put the car on the road yet. I'm about to trailer it to Stark fla. just to the front end lined-up, its hard to find an old school gear head that knows anything about these Mopars. It has 4.11 gears , 29/18.50-15 and 3500 stall
it runs rich at idel. I'm going to bring it up to temp this week end and try to adjust the timing better and work on the carb, I recall the 4 corner screws are about 2 complete turns out. I may need to remove it from the intake and check the, I believe you said transfer slot on the primary side.

 

[AJ/FormS]

OK I'm in trouble; I have never worked on a 4-corner idle carb.
What I want to know is how do you know the Idle is rich?
I ran the 292/292/108 in my Hi-compression 367 for one summer with OOTB Edlebrock Alloy heads, an AirGap, and an ancient 750DP.
I ran it at 14* Idle advance with a manual trans; and the cylinder pressure was over 185psi. After setting the Transfer slot sync, as previously described, I had to introduce some Idle Bypass Air. I tried cracking the secondaries on my DP, but without fuel in that bypass air, it idled kindof crappy. IMO, the bypass air has to come in close to the Idle discharge fuel ports. So to that end, I did this by drilling ONE tiny hole in each Primary throttle blade. I started at 1/16, and went up by 32nds. I ended up at 1/8, but that was too big, the transfers dried up on me before I knew what was happening. So I filled the holes with solder, moved over, and started again. I spent a lot of time at 5/64, but IIRC I ended up at around 6or possibly at 7/64ths.

With a 4-corner carb, you can just crack the secondaries, and adjust the secondary idle-fuel screws, as may be necessary.
My guess is that you might be able to set them all the same, but I really have NO IDEA.
The principal thing to remember is this;
On the Primary side, there are THREE fuel-ports to deliver Idle fuel, namely;
1) the transfer slots,
2) the Idle-discharge ports, and
3) right beside those are the trimmers which are adjustable by the "mixture screws".
All of those circuits are modified in the Fuel-wells by Air coming down the bleeds.
Idle-air is supplied by the cracked Primary throttle blades PLUS the PCV system, Plus whatever bypass air you introduce on the Secondary side.
I idled that cam at ~750/800 with a manual trans, and IIRC the Manifold Vacuum at 14* timing was a tad under 10 inches.
To get the low-rpm timing back, I installed a two-step curve from a smog 318. That spring set has two different springs, one of them has a long loop. This spring does nothing until the rpm gets up to about, in my case, 2800. So the regular spring allows the timing to advance fairly fast. I had to be careful to not allow any mechanical advance below about 900rpm. From there the timing jumped linearly to 28* at 2800rpm, then slowed down and the all-in was 34* @3400rpm., which was by the springs combined. As you might guess, this took me all summer to achieve.
To get the cruise timing, I modified the V-can to 22* by filing the stops partly off. I think you can do this to any 70s V-can. My Eddy-headed 367 liked over 56* of cruise timing.
There, that will get you started.
Your 340 may, of course, have slightly different requirements.
And, OOps more coming, the wife is calling for supper

And let's not forget;
1) in at 104* that cam has an Ica of 70*, which leaves you just 110* of compression time
2) The overlap period is 76 degrees.
3) the power-stroke is just 102*
4) with the piston at TDC on the overlap phase, 42* are allocated to the intake stroke and 34* go to the exhaust. With BOTH valves are slightly opened at this point. The headers are supposed to be encouraging the AF charge to get moving from the plenum into the Combustion chamber, before the piston gets started on that job. But with the piston now at TDC, the header will continue to pull on the intake until the exhaust valve closes some 34 degrees later.
What this means to your engine is this;
If the headers are working really well, they will pull some of the fresh F/A charge straight across the piston and into the pipes. If your headers are sucking air at the heads, then fresh air will also be in there. If that fuel ignites and burns, the expanding gasses can easily feed back into the combustion chamber thru the open exhaust valves.
When the exhaust valve finally closes, the piston is moving down and the atmosphere begins working earnestly to fill the cylinder. When the piston hits bottom and turns around, it will be another70 degrees before the intake valve closes, soooooo the piston is well on it's way up when that happens. At low rpm, the piston will push some of the just-inducted A/F charge back into the plenum, thus reducing your Idle-vacuum.
The thing of it is, with a 3.315 stroke and the intake closing at 70* ABDC, your EFFECTIVE stroke is reduced to 2.43 inches. That means that the piston is .885 up from the bottom when this happens or ~27% of the way.

I tell you all this, just to say, that there is a whole lotta stuff going on inside your intake manifold. So I ask again; how do you know the Idle is rich?

BTW:
What is your local elevation?

 

[D.Coulter]

OK I'm in trouble; I have never worked on a 4-corner idle carb.
What I want to know is how do you know the Idle is rich?
I ran the 292/292/108 in my Hi-compression 367 for one summer with OOTB Edlebrock Alloy heads, an AirGap, and an ancient 750DP.
I ran it at 14* Idle advance with a manual trans; and the cylinder pressure was over 185psi. After setting the Transfer slot sync, as previously described, I had to introduce some Idle Bypass Air. I tried cracking the secondaries on my DP, but without fuel in that bypass air, it idled kindof crappy. IMO, the bypass air has to come in close to the Idle discharge fuel ports. So to that end, I did this by drilling ONE tiny hole in each Primary throttle blade. I started at 1/16, and went up by 32nds. I ended up at 1/8, but that was too big, the transfers dried up on me before I knew what was happening. So I filled the holes with solder, moved over, and started again. I spent a lot of time at 5/64, but IIRC I ended up at around 6or possibly at 7/64ths.

With a 4-corner carb, you can just crack the secondaries, and adjust the secondary idle-fuel screws, as may be necessary.
My guess is that you might be able to set them all the same, but I really have NO IDEA.
The principal thing to remember is this;
On the Primary side, there are THREE fuel-ports to deliver Idle fuel, namely;
1) the transfer slots,
2) the Idle-discharge ports, and
3) right beside those are the trimmers which are adjustable by the "mixture screws".
All of those circuits are modified in the Fuel-wells by Air coming down the bleeds.
Idle-air is supplied by the cracked Primary throttle blades PLUS the PCV system, Plus whatever bypass air you introduce on the Secondary side.
I idled that cam at ~750/800 with a manual trans, and IIRC the Manifold Vacuum at 14* timing was a tad under 10 inches.
To get the low-rpm timing back, I installed a two-step curve from a smog 318. That spring set has two different springs, one of them has a long loop. This spring does nothing until the rpm gets up to about, in my case, 2800. So the regular spring allows the timing to advance fairly fast. I had to be careful to not allow any mechanical advance below about 900rpm. From there the timing jumped linearly to 28* at 2800rpm, then slowed down and the all-in was 34* @3400rpm., which was by the springs combined. As you might guess, this took me all summer to achieve.
To get the cruise timing, I modified the V-can to 22* by filing the stops partly off. I think you can do this to any 70s V-can. My Eddy-headed 367 liked over 56* of cruise timing.
There, that will get you started.
Your 340 may, of course, have slightly different requirements.
And, OOps more coming, the wife is calling for supper

And let's not forget;
1) in at 104* that cam has an Ica of 70*, which leaves you just 110* of compression time
2) The overlap period is 76 degrees.
3) the power-stroke is just 102*
4) with the piston at TDC on the overlap phase, 42* are allocated to the intake stroke and 34* go to the exhaust. With BOTH valves are slightly opened at this point. The headers are supposed to be encouraging the AF charge to get moving from the plenum into the Combustion chamber, before the piston gets started on that job. But with the piston now at TDC, the header will continue to pull on the intake until the exhaust valve closes some 34 degrees later.
What this means to your engine is this;
If the headers are working really well, they will pull some of the fresh F/A charge straight across the piston and into the pipes. If your headers are sucking air at the heads, then fresh air will also be in there. If that fuel ignites and burns, the expanding gasses can easily feed back into the combustion chamber thru the open exhaust valves.
When the exhaust valve finally closes, the piston is moving down and the atmosphere begins working earnestly to fill the cylinder. When the piston hits bottom and turns around, it will be another70 degrees before the intake valve closes, soooooo the piston is well on it's way up when that happens. At low rpm, the piston will push some of the just-inducted A/F charge back into the plenum, thus reducing your Idle-vacuum.
The thing of it is, with a 3.315 stroke and the intake closing at 70* ABDC, your EFFECTIVE stroke is reduced to 2.43 inches. That means that the piston is .885 up from the bottom when this happens or ~27% of the way.

I tell you all this, just to say, that there is a whole lotta stuff going on inside your intake manifold. So I ask again; how do you know the Idle is rich?

BTW:
What is your local elevation?

hello again, i know its running rich because the plugs are fuel fouled and the exhaust will run you out the the shop in about 5 minutes. lol
i live in florida, high humidity

 

[D.Coulter]

OK I'm in trouble; I have never worked on a 4-corner idle carb.
What I want to know is how do you know the Idle is rich?
I ran the 292/292/108 in my Hi-compression 367 for one summer with OOTB Edlebrock Alloy heads, an AirGap, and an ancient 750DP.
I ran it at 14* Idle advance with a manual trans; and the cylinder pressure was over 185psi. After setting the Transfer slot sync, as previously described, I had to introduce some Idle Bypass Air. I tried cracking the secondaries on my DP, but without fuel in that bypass air, it idled kindof crappy. IMO, the bypass air has to come in close to the Idle discharge fuel ports. So to that end, I did this by drilling ONE tiny hole in each Primary throttle blade. I started at 1/16, and went up by 32nds. I ended up at 1/8, but that was too big, the transfers dried up on me before I knew what was happening. So I filled the holes with solder, moved over, and started again. I spent a lot of time at 5/64, but IIRC I ended up at around 6or possibly at 7/64ths.

With a 4-corner carb, you can just crack the secondaries, and adjust the secondary idle-fuel screws, as may be necessary.
My guess is that you might be able to set them all the same, but I really have NO IDEA.
The principal thing to remember is this;
On the Primary side, there are THREE fuel-ports to deliver Idle fuel, namely;
1) the transfer slots,
2) the Idle-discharge ports, and
3) right beside those are the trimmers which are adjustable by the "mixture screws".
All of those circuits are modified in the Fuel-wells by Air coming down the bleeds.
Idle-air is supplied by the cracked Primary throttle blades PLUS the PCV system, Plus whatever bypass air you introduce on the Secondary side.
I idled that cam at ~750/800 with a manual trans, and IIRC the Manifold Vacuum at 14* timing was a tad under 10 inches.
To get the low-rpm timing back, I installed a two-step curve from a smog 318. That spring set has two different springs, one of them has a long loop. This spring does nothing until the rpm gets up to about, in my case, 2800. So the regular spring allows the timing to advance fairly fast. I had to be careful to not allow any mechanical advance below about 900rpm. From there the timing jumped linearly to 28* at 2800rpm, then slowed down and the all-in was 34* @3400rpm., which was by the springs combined. As you might guess, this took me all summer to achieve.
To get the cruise timing, I modified the V-can to 22* by filing the stops partly off. I think you can do this to any 70s V-can. My Eddy-headed 367 liked over 56* of cruise timing.
There, that will get you started.
Your 340 may, of course, have slightly different requirements.
And, OOps more coming, the wife is calling for supper

And let's not forget;
1) in at 104* that cam has an Ica of 70*, which leaves you just 110* of compression time
2) The overlap period is 76 degrees.
3) the power-stroke is just 102*
4) with the piston at TDC on the overlap phase, 42* are allocated to the intake stroke and 34* go to the exhaust. With BOTH valves are slightly opened at this point. The headers are supposed to be encouraging the AF charge to get moving from the plenum into the Combustion chamber, before the piston gets started on that job. But with the piston now at TDC, the header will continue to pull on the intake until the exhaust valve closes some 34 degrees later.
What this means to your engine is this;
If the headers are working really well, they will pull some of the fresh F/A charge straight across the piston and into the pipes. If your headers are sucking air at the heads, then fresh air will also be in there. If that fuel ignites and burns, the expanding gasses can easily feed back into the combustion chamber thru the open exhaust valves.
When the exhaust valve finally closes, the piston is moving down and the atmosphere begins working earnestly to fill the cylinder. When the piston hits bottom and turns around, it will be another70 degrees before the intake valve closes, soooooo the piston is well on it's way up when that happens. At low rpm, the piston will push some of the just-inducted A/F charge back into the plenum, thus reducing your Idle-vacuum.
The thing of it is, with a 3.315 stroke and the intake closing at 70* ABDC, your EFFECTIVE stroke is reduced to 2.43 inches. That means that the piston is .885 up from the bottom when this happens or ~27% of the way.

I tell you all this, just to say, that there is a whole lotta stuff going on inside your intake manifold. So I ask again; how do you know the Idle is rich?

BTW:
What is your local elevation?

if you get a chance take a look at the black diamond 750 by quick fuel holley performance

 

[AJ/FormS]

hello again, i know its running rich because the plugs are fuel fouled and the exhaust will run you out the the shop in about 5 minutes. lol

OK now we are getting somewhere.
That stink,
if it burns your eyes,
is NOT running rich; NOT rich.
You will not get rid of it by doing any carb adjustment, by itself.
Well actually it is rich but not for the reason you might think.
So my next question is this;
does the stink burn your eyes?

refresh your screen, I am editing as I go.
you said;

Full MSD ignition. Set at 32 degrees advance @2000 rpm. Full tub w/cage, 4 wheel disc break. It's a complete street car.

Do a compression test and post up the results.
What is the coolant temperature at idle?
What is your local elevation?
Do you recall what the installed centerline of the 292cam might be?
Is that the 292/292...... the 108Lsa cam?
Are your roller rockers adjustable?
What sparkplugs are in it?
Do you recall what the ring-gaps were set to? Does the engine mysteriously lose oil level?
Are you running a PCV?

As for the PCV System;
You MUST run a PCV plumbed to the underside of, and between, the Primary Throttle blades. If your carb is NOT set up for this, and it was mine, I would drill and tap the intake as close to that position as I could.
If your carb has a port at the back, between the Secondaries, I suppose you could, with a 4-corner carb use that, and since I have never run a 4-corner, I guess I would try it.
But, with a regular carb, my experience is this;
Running the PCV off the back is guaranteed to make the idle-exhaust stink, as the rear cylinders run lean. The tendency is to richen the Primaries to get fuel back there, but now the Front cylinders run too rich. So you end up going from bad to worse. So I just never run that configuration.
Additionally I never run the Booster charge hose to just one of the rear cylinders.That charge hose, with the 292 cam is constantly shuttling air as the vacuum at low rpm is so low, so then whatever cylinder it is plumbed to is having it's airflow constantly being upset. You can plumb it to that rear port on the carb, if you have one there. If your carb does not have one back there, then drill and tap the intake PLENUM in/near that location. This will smooth the signal to the booster as well. DO NOT Tee the PCV and the Booster charge line together. Make sure your valve-cover Breather is well baffled in the cover and to avoid the mess on the VC at WOT, I run an enclosed-type breather with a fat breather hose on it looped up and over so any oil trying to get out, runs back into the breather and at shut down, drains back into the engine. If you are running the factory type air-cleaner housing, then use the factory system. But with a 292 cam you should be running fresh air from above the hood or from the front of the car, either works on the street.
The PCV is NOT an option.

If your engine is mysteriously losing oil level, with no visible external evidence, I can guarantee you that she is sending it out the tailpipes. You gotta fix this because more than half of the times that I run into burning eyes, that oil is a major contributor to the cause of it.
In some cases that oil loss is from fuel-wash on the cylinders from a too-rich low-speed, and/or Part Throttle circuit. To combat that, I run what some say is a too small MJ, but my 10.5 PV comes in early enough to cover the loss of fuel, and I never feel a lean hesitation. This strategy also gets me great fuel mileage in steady-state running.
To prove oil-burning just swab the inside of your Tailpipes. Do not confuse Soot from oily residue. I just taste it.
BTW
your tailpipes should not be sooty with the MSD ignition system.
Your tailpipes should NOT be black at all, rather tan to white-ish but not full-white. Black might be OK as long as it is not sooty. It should take a fair bit of pressure to swab blackness out on your fingertips.
Full-white is too lean and dangerously close to a melt-down.
Other things that can cause oil-burning are; the oilrings stuck in the grooves, tapered cylinder walls, out of round cylinder walls or gouges in the cylinder walls, baggy oil-ring gaps, lousy umbrella seals, and excessive cylinder oiling coming from the rod-jets. You do not need 20W50 oil either, 10W30 is just fine. The Second compression ring is NOT an oil-ring and does a lousy job of removing it off the walls. It's not even a good second compression ring,lol.
So if you are loosing oil, find out the cause and fix it. Nothing can really be done with the stinky exhaust until you have proved it ain't burning oil.

After that, yur not gonna like me, cuz you are gonna have to sacrifice some low-rpm timing.
I know, I know; all that timing makes the little 292-cammed 340 more peppy at lower rpms, but 32* at 2000rpm is just too much and way too early. And if you don't have a Vcan, or if it's hooked up to manifold vacuum. you are gonna like me even less.
From an earlier post;

Full MSD ignition. Set at 32 degrees advance @2000 rpm.

I idled that cam at ~750/800 with a manual trans, and IIRC the Manifold Vacuum at 14* timing was a tad under 10 inches.

"" To get the low-rpm timing back, I installed a two-step curve from a smog 318. That spring set has two different springs, one of them has a long loop. This spring does nothing until the rpm gets up to about, in my case, 2800. So the regular spring allows the timing to advance fairly fast. I had to be careful to not allow any mechanical advance below about 900rpm. From there the timing jumped linearly to 28* at 2800rpm, then slowed down and the all-in was 34* @3400rpm., which was by the springs combined. As you might guess, this took me all summer to achieve.
To get the cruise timing, I modified the V-can to 22* by filing the stops partly off. I think you can do this to any 70s V-can. My Eddy-headed 367 liked over 56* of cruise timing.
There, that will get you started.
Your 340 may, of course, have slightly different requirements. ""
This is the timing I ran on my 292/292/108, with excellent results.

You can argue all you like, lol, but the stink will not go away until the Idle-timing is down around 14* plus/minus 2*, AND the carb adjusted as per the Transfer-slot synchronization technique; BOTH together.

Now, like said, your 340 might be slightly different.
Here's how you can know that the low-speed circuit is right;
Number one; no more stinky exhaust, lol
2) after the warm up, you can put her in first gear and she will idle down to 550 while pulling herself and NOT get jumpy, until about 500rpm. If your 292-cammed 340 will not pull herself at 550 rpm in First gear with a Manual-trans, the low-speed circuit is not right. The first thing to try is LESS idle-timing ! My 367 does that with 5 measely degrees of advance. The more advance that you give it, the more powerful the engine will become, and the power pulses will hammer the driveshaft and the car will get more and more jumpy until you are forced to clutch it, and start over.
3) with the car in first gear and rolling, she will take throttle right away with no stumble,hesitation, nor a sag of any kind. It may not take WOT, I'm not saying that, but you should be able to drive away briskly like it was an automatic.
4) you don't care what the plugs look like after idling all day. You have an MSD; if the fire goes out on the first spark, the MSD will just keep on relighting it. You cannot tune that cam to an AFR of any kind at idle, so let it be what it will be... If you keep leaning the idle out, to try to clean up the plugs, you will only create other issues.
Ok a brief explanation;
All Four-Stroke Internal combustion engines have exactly one best place for peak cylinder pressure to occur to put the most amount of energy into the crank. This is variously said to be 25 to 28 degrees AFTER TDC Compression. ALL your timing systems are, from the factory, or were before the smog era, designed to peak at that spot. Now, it is your job to find it, and design your ignition system to do it.
However, you cannot run that at Idle because your big fat 340 will be TOO powerful, the rpm will runaway on you.
Want proof?
Go out and warm up your engine, then grab the Distributor and start advancing it without checking the timing. Keep advancing it until the rpm no longer rises. NOW check the timing at the highest rpm. What did you get? I have seen numbers deep into the 30s and even into the 40s and occasionally into the 50s if the rpm runs over 2200rpm. Put your timing back.
Whatever number you got, that is the amount of advance your engine was HAPPY about at whatever the rpm got up to, AND in all likelihood was in the window of creating peak pressure at the magic 25 to 28 degrees AFTER TDC. But obviously, you cannot drive it like that. But you can engineer your timing systems to get there at that rpm and the engine will be very very peppy there and get great fuel economy at that peak pressure setting.
If you advance the timing more from there, the peak pressure will arrive too early and slam the piston/rod onto the crank , doing a lotta pushing but less actual work. This is hard on parts and in some cases produces audible detonation which if allowed to continue will break parts.
If retard the timing from there; the engine will not achieve it's full potential, as the expanding gasses chase after the descending piston. You can use this to your advantage to soften the power at low-rpm, and specifically at idle. For those that have automatics and low-stall convertors, such a powerful idle only serves to cause the trans to bang when going into gear, and the engine immediately loses rpm as the TC drags it down.
The point is this, ask 20 guys where to set the idle-timing of your 292 cammed 340 and they will almost invariably give you a high numberr and then you spend the rest of the summer trying to tune it........... like I did. Forget that chit. Let the engine tell you what the timing should be, by setting the T-slot sync, and using timing to set the rpm. Just retard the timing from your 20* until the engine stalls and then give some back, lol. With a manual trans, that's all there is to it. wait, you have a 4-speed right? Lemmee go check.
Oh no! you said 3500 stall, lol. Well then
who cares about the idle-timing........ so long as she doesn't bang or stall going into gear..... right?
On the street .....Wrong!
You still want the low-speed operation below stall, to be enjoyable; so everything I have said to this point still applies, except you can run more low-speed timing because, the engine is never required to be under full-load below stall, so detonation is less of an issue. BUT, the idle is still pretty important, so basically, nothing much has changed.
So how do you get that "more low-speed timing? "
That's what the Vacuum advance is for.
After your basic advances are established you can use the V-can to fill in the rest, below stall .

Go out and map your advance curve, having disconnected the Vacuum advance. Just take the rpm up in 400rpm steps and record the amounts. You need to do this so that when you make changes, you will know if you are going in the right direction.
Next repeat the test with the V-can back on line.
Next repeat the exercise, still with the Vcan on line, but just twist the distributor at say 2000rpm, and keep it there while simultaneously advancing the timing.This will require you to close the throttle as you go.
When the rpm no longer climbs from 2000, read the timing and record it. Then repeat this at every 400 rpm until you hit 3600rpm.
Now plot the numbers on graph paper, and compare the results.
The first set is what you got for Power-timing.
the Second set, is what the engine can muster for Part-Throttle.
The Third set is what the engine wants, with no load on it. How close are the lines?
After about 3600 all open-chambered iron-headed SBMs want about the same POWER TIMING of ~36*, while closed-chamber alloy-heads seem to be happy with 2 to 4 degrees less.
Your job, as the tuner, is to try to give the engine what she wants for as many conditions as you can. Your job is NOT to force timing on her. On the street you will not, by the seat of your pants, feel 3* short of optimum, so don't sweat the shortage of 3 degrees. Rather be alarmed if too much timing causes detonation. This must not be allowed.
Here's the bottom line;
I don't have a dyno, but I have watched dozens and dozens of tests, and the result seems to always be the same. The last two or three degrees at WOT, are worth no more than 7hp at the peak! Less is the norm. How often, on the street, is your 292-cammed 340, gonna be at WOT AT ~5300, in a gear that does not spin your tires. If the tires are spinning, you already have more power than the suspension and tires can handle.... so is 7 hp gonna ruin your day?
I hardly think so, lol.
BTW
5300@WOT, with 3.55s is about 45mph in First, maybe77 in Second, maybe 112 in DRive, lol, with 27" tires. In other words, for most of us, when the tires stop spinning, we have already been speeding for quite a while. So really, First gear is the only gear that is gonna run up to the PowerPeak, and the tires are usually still spinning, so no you will never miss those 7 hp.

So having come to that assessment, you can confidently build your timing curve to add the amount of PowerTiming, to whatever Idle-timing your engine is telling you to try. Suppose the engine want 14* and the PowerTiming is gonna be 34*; this means that the mechanical system has to provide 34 less 14 = 20* How easy is that!
The next part is not as easy, and goes back to the above quote, which I will repeat here;

I idled that cam at ~750/800 with a manual trans, and IIRC the Manifold Vacuum at 14* timing was a tad under 10 inches.
"" To get the low-rpm timing back, I installed a two-step curve from a smog 318. That spring set has two different springs, one of them has a long loop. This spring does nothing until the rpm gets up to about, in my case, 2800. So the regular spring allows the timing to advance fairly fast. I had to be careful to not allow any mechanical advance below about 900rpm. From there the timing jumped linearly to 28* at 2800rpm, then slowed down and the all-in was 34* @3400rpm., which was by the springs combined. As you might guess, this took me all summer to achieve.

Once you have modified your distributor, you repeat the "What have I got Test" and plot the new no-load numbers then compare them to what the engine wants. Are you closer? There may be some rpms that you are and others may not be close at all, but what you are looking for is the shape of the existing curve to the desired curve. Then you bring your V-can back on line and see how close you are to the desired line, then modify IT ! lol, to get as close as you can.
This is a lot of work and takes a lot of time and you really only want to do it once, so it behooves you to get the idle right before you do anything else..... I gotta tell ya, nothing gets me going than hearing a car idling around the parking lot, with a great tune in it, cuz I know how hard that can be.
And when it mine doing that with a 4-speed, well, I can safely say, I like that tune, and I like that AJ guy, lol.

Ok that's it for today, I got some chores to do.
refresh your screen one last time.