Proper Transfer Slot Position

[Hysteric]

18 degress initial isnt too bad but you could lower it to some where around 14 to 16 and see if gives you what you're after.

Also that chamber (magnum) wont need 38 degrees total timing unless its lean. Try 32 degrees total and work from there.

 

[jmanhoff]

18 degress initial isnt too bad but you could lower it to some where around 14 to 16 and see if gives you what you're after.

Also that chamber (magnum) wont need 38 degrees total timing unless its lean. Try 32 degrees total and work from there.

I’m going to throw that adjustable spring kit in and start from there. These are the specs of it on paper, but of course I’ll remap it with what it’s actually doing.

 

[mbaird]

18 degress initial isnt too bad but you could lower it to some where around 14 to 16 and see if gives you what you're after.

Also that chamber (magnum) wont need 38 degrees total timing unless its lean. Try 32 degrees total and work from there.

Hysteric is correct. My magnum headed engine only needs about 32* of total mechanical.
I may have missed this but are you running ported or manifold vacuum advance ? Or is there no VA on that distributor ?

 

[jmanhoff]

Hysteric is correct. My magnum headed engine only needs about 32* of total mechanical.
I may have missed this but are you running ported or manifold vacuum advance ? Or is there no VA on that distributor ?

I’m running ported, I know the mopars ran ported basically forever, and it’s also a basically bone stock engine, so manifold advance is overkill and I actually tried it once before and could never get the idle below 1000rpm lol.

Would it make more sense to have a higher initial timing and put in limiter bushings/block off the slot on the weights, or have lower initial timing to tune what the total advance is? In my head it makes sense to set the initial timing to somewhere between 12-18 wherever I can get the idle where I want it to be, then set the total advance somewhere around 32-34 (I’m assuming I just listen for pinging and then back it off with the bushings until I don’t hear it at all?)

 

[mbaird]

I’m running ported, I know the mopars ran ported basically forever, and it’s also a basically bone stock engine, so manifold advance is overkill and I actually tried it once before and could never get the idle below 1000rpm lol.

Would it make more sense to have a higher initial timing and put in limiter bushings/block off the slot on the weights, or have lower initial timing to tune what the total advance is? In my head it makes sense to set the initial timing to somewhere between 12-18 wherever I can get the idle where I want it to be, then set the total advance somewhere around 32-34 (I’m assuming I just listen for pinging and then back it off with the bushings until I don’t hear it at all?)

Actually Mopar ran manifold vacuum originally. Ported was for emissions. I don’t have a bias towards either one . It’s whatever works best for the build . All (most) of our builds have been modified so what the factory did has no bearing on.
I was thinking you might be running manifold and that may be contributing to your issue .

 

[mbaird]

BTW , that build is begging for a Thermoquad ! Lol

 

[jmanhoff]

BTW , that build is begging for a Thermoquad ! Lol

I’ll be honest, the only reason I went with a double pumper is because my dad recommended it lol. I know holleys are a never ending game of tinkering but honestly a part of me doesn’t want to just throw a carb on it and tune it once and be done with it, it’s really fun to tinker with it because I get to learn how the circuits work and influence each other. If it wasn’t obvious already I really have no idea what I’m doing, I’m just trying to learn and ask stupid questions lol. I’m 22 so I was born after the last production car drove off the line with a carb, so I didn’t exactly grow up messing with them lol

 

[jmanhoff]

Is there any goals that I should shoot for in terms of what my curve looks like? I know you can get “close enough” with certain specs, but every engine wants something different so it’s not a do this and just send it sort of deal.

 

[mbaird]

I’ll be honest, the only reason I went with a double pumper is because my dad recommended it lol. I know holleys are a never ending game of tinkering but honestly a part of me doesn’t want to just throw a carb on it and tune it once and be done with it, it’s really fun to tinker with it because I get to learn how the circuits work and influence each other. If it wasn’t obvious already I really have no idea what I’m doing, I’m just trying to learn and ask stupid questions lol. I’m 22 so I was born after the last production car drove off the line with a carb, so I didn’t exactly grow up messing with them lol

I have nothing against Holleys or double pumpers . I was just thinking if this is in a daily driver truck a TQ would really shine ! AND get good mpg/ driveability.

 

[jmanhoff]

I have nothing against Holleys or double pumpers . I was just thinking if this is in a daily driver truck a TQ would really shine ! AND get good mpg/ driveability.

Now allegedly, ALLEGEDLY, you can tune a Holley to get the same mpg as an edelbrock or a quad, while still having the benefits of it being a Holley. But honestly, my expectations are not very high for mpg. If I can get 12-13mpg city, and 19-20 highway I will be a happy camper. Currently I’m at about 10.5 city, not too sure highway. Given it’s a truck, I’m also dealing with aerodynamics on the highway which is a large part of the mpg there, but if I can crank out as much ignition advance as I can paired with the leanest it will run while not bucking, then I should be able to get 20. The highest I’ve seen with no aero (not even a front valence) and I think at the time 30 degrees total timing with about 14.5:1 or so on the AFR, was 17mpg so I think 20 is possible

 

[Mattax]

Actually Mopar ran manifold vacuum originally. Ported was for emissions.

Nope. False information/belief and I was as guilty as the next guy, until a coupe of old timers set me straight. I trusted their examples (non-mopar) were correct but was it broadly true. Start looking through old shop manuals and at mid 60s muscle cars and turns out they were right. Nothing to do with emmisions. Go ahead take a look for yourself. I've posted a snip out the 1959 Chrysler Master Tech Conference, long before anything emissions were a concern (other than doing awaywith draft tubes). I've also posted photos showing Chevy's vacuum hose routing on some of their high performance. On Speedtalk forum someone pulled out an Audell's that showed ported vacuum for distributor advance from at least a decade earlier.

 

[jmanhoff]

Nope. False information/belief and I was as guilty as the next guy, until a coupe of old timers set me straight. I trusted their examples (non-mopar) were correct but was it broadly true. Start looking through old shop manuals and at mid 60s muscle cars and turns out they were right. Nothing to do with emmisions. Go ahead take a look for yourself. I've posted a snip out the 1959 Chrysler Master Tech Conference, long before anything emissions were a concern (other than doing awaywith draft tubes). I've also posted photos showing Chevy's vacuum hose routing on some of their high performance. On Speedtalk forum someone pulled out an Audell's that showed ported vacuum for distributor advance from at least a decade earlier.

A little off topic but I’m just curious if you have a good explanation. How does ported vacuum help over manifold vacuum? Aren’t they basically equal once the throttle blades are open? I watched a video from thunderhead289 and he hooked a vac gauge to the ported vacuum port and one to manifold, and at idle ported read zero of course, but once he cracked the throttle they both read the same across the board

 

[Mattax]

It's a stock engine so the baseline is the factory setup. You have to have a bit of understanding of what timing does and why and when advance is needed. Then it becomes a little more obvious why a 4 bbls got a slightly different curve than a 2 bbl, and so forth. Since the magnum 5.9 went into the era of EFI you can look at the factory map, as well as the aftermarket maps including mopars. Those can be turned into a more or less equivalent distributor setup. Try searching in the forum as I'm pretty sure they've been discussed here.

With a true Delco distributor, you'll probably best with two equal springs. Definately true for some of the copies. So you might have to run more intial 'cause the advance is going to be fairly linear. (Ford and Chrysler distributor advances can be shaped.) In the tapatalk Racing Fuel Systems forum, look for Tuner's post aboout modifying the GM type advance if needed.

 

[Mattax]

A little off topic but I’m just curious if you have a good explanation. How does ported vacuum help over manifold vacuum? Aren’t they basically equal once the throttle blades are open? I watched a video from thunderhead289 and he hooked a vac gauge to the ported vacuum port and one to manifold, and at idle ported read zero of course, but once he cracked the throttle they both read the same across the board

Its not about one helping over another. Its about using the tools available to get the timing wanted.
A couple of companies used venturi vacuum to control timing.
Using weights for rpm related advance, and ported for density related advance is that each is just does their thing.

 

[jmanhoff]

Okay, that actually is really clear to understand lol. After a brief search for what people typically time their magnums with, it seems like it hovers around 10-15 initial and no more than 34 total, and the EFI magnums differ slightly depending on what they were put in. I read that the grand cherokees were 32-34 degrees, while the rams were 27. I’m probably going to drop the initial down to 14 degrees, and limit the mechanical to 34 total. Just have to find the best spring setup to not throw in the advance too soon

 

[Mattax]

What timing does was posted before. Post 226

Post in thread 'Fine Tuning a 360 Magnum with a Brawler "Double Pumper"'

Feb 8, 2025

Lol I’m also just a really stubborn traditionalist because my dad grew up with mopars and holleys so I’m kind of just following the same road.

To be frank you're throwing darts blindly. Pin the tail on the donkey without seeing the donkey.
The first thing you need to do to seperate wheat from chaff is know the difference.

Go read the booklets from Chrysler on carburetor fundementals.
Its free at available at your electronic fingertips. Urich and Fisher will have to be found or ordered from ebay or 'zon so you won't get it for a week. Its not that its a great book, but the...

• Mattax

The Master tech Index was posted too.

Post in thread 'Fine Tuning a 360 Magnum with a Brawler "Double Pumper"'

Feb 6, 2025

Yeah I’ve just been poking around with random things to see if I can get it dialed in again.

I'll say the same as three other guys said. Stop. Write everything down and approach this systematically.
These carbs (I'm including carters, Rochesters and most of the downdraft 4bbls we deal with) have a low speed circuit that is feed from the main or high speed circuit. Get the low speed established first, beginning with idle. The low speed or idle circuit works off of the pressure difference (vacuum) below the throttle plates. It is most effective with high vaccum in providing good...

• Mattax

Along with a link to a thread showing transfer slot setup

Post in thread 'Holley 750 "stumbles" on WOT'

Jan 6, 2025

when stomping it to the floor from a dead stop, it would hesitate for about 1 or 2 seconds then WAHHHHHH
He replaced it with an identical new carb and his problem was solved.

Tough diagnoses only because he claimed no other changes besides changing carbs.
Always begin with correct fuel level.
The jets and accelerator pump inlets are low and at the bottom. However it is possible the fuel level in bowls were low.

Next, check for contact between pump arm and pump cam at idle. This is something that someone could change when adjusting idle speed with the stop screw and not think it...

• Mattax

 

[mbaird]

Nope. False information/belief and I was as guilty as the next guy, until a coupe of old timers set me straight. I trusted their examples (non-mopar) were correct but was it broadly true. Start looking through old shop manuals and at mid 60s muscle cars and turns out they were right. Nothing to do with emmisions. Go ahead take a look for yourself. I've posted a snip out the 1959 Chrysler Master Tech Conference, long before anything emissions were a concern (other than doing awaywith draft tubes). I've also posted photos showing Chevy's vacuum hose routing on some of their high performance. On Speedtalk forum someone pulled out an Audell's that showed ported vacuum for distributor advance from at least a decade earlier.

I will not doubt your input since you seem to have proven your knowledge over the years but my research has led me to believe that early mopars used manifold vacuum in the 60s . In fact if I remember correctly I have had carbs with no ported nipple. But either way the us of ported vs manifold is dependent on the build .

Manifold ports engage the advance all the time and ported only engages past idle .

 

[Mattax]

I will not doubt your input since you seem to have proven your knowledge over the years but my research has led me to believe that early mopars used manifold vacuum in the 60s . In fact if I remember correctly I have had carbs with no ported nipple. But either way the us of ported vs manifold is dependent on the build .

Manifold ports engage the advance all the time and ported only engages past idle .

When you have a chance, go look. So far everyone who has looked (inlcuding me) has not come up with a Chrysler example using a manifold source. But that doesn't mean there aren't any. I think what happened is the smogged engines generally had retarded initial timing. Connecting the vacuum advance to a manifold source brought the idle timing up closer to pre-emissions. Probably a bit too high for stock but seemed better, and probably pretty close to where a hot rodded engine might like assuming it had OK vacuum at idle. Easy win even if the explanation was conjectural. I mean gosh, most of us didn't access to the amount of info or people we do now.

 

[Mattax]

Post in thread 'Ported or manifold Vacuum to Dist.'

Oct 12, 2019

'67 AFBs, Vacuum advance connection is pretty high.
View attachment 1715407111

The spark port is about middle of the transfer slots, way above the idle discharge port.
View attachment 1715407114

Be interesting to see if other versions were different.

Hey Matt, I dug out my carb. You were right. Looks like ported vacuum. The nipple is quite high though. A strange looking slot though.

View attachment 1715407401

• toolmanmike

Post in thread 'Good Initial Timing and Too much Total Timing Problem. Seeking guidance to minimize total timing. 1969 Swinger 340 4 Gear'

Jun 6, 2024

Emissions & Timing.

Chrysler's answer to reduce excessive HC and CO was to make idle fuel mixtures leaner and at the same time retard the timing at idle. Reducing the initial timing put more heat into the cylinder wall (burn completes while the piston is further down the hole) at idle. To make up for the loss in power, idle speed was bumped up - especially needed with automatic transmissions.

The 340 was released in '68; all came with CAP (Clean Air Package) AFAIK.
So lets look at timing for a 273 4bbl to see how these idle settings in the CAP package were compensated for in the...

• Mattax

 

[Mattax]

Okay, that actually is really clear to understand lol. After a brief search for what people typically time their magnums with, it seems like it hovers around 10-15 initial and no more than 34 total, and the EFI magnums differ slightly depending on what they were put in. I read that the grand cherokees were 32-34 degrees, while the rams were 27. I’m probably going to drop the initial down to 14 degrees, and limit the mechanical to 34 total. Just have to find the best spring setup to not throw in the advance too soon

I don't know where you're searching here. here's one

Thread 'Need some help with my timing curve.'

Dec 14, 2022

So after running an eBay Ready-to-Run Hei distributor for the past 5-6 years, I finally got around to putting a timing light on it and mapping out the advance curve. Come to find out, the curve was severely lacking! I ended up swapping out that distributor with a factory electronic distributor that I left the factory light spring in it and swapped out the heavy long looped spring with a black spring from the Fbo spring kit.
Here are the two curves laid over a graph that I saw @Mattax post on here a few times.
The R2R curve starts at 18 initial, overlaps the new distributors curve...

• 75slant6

 

[jmanhoff]

I was doing google searches, a lot of it was it finding specific posts from random threads on different mopar forums.

I’m gonna go buy a notebook for all my tuning and engine notes for the future aka this weekend lol.

First thing I’m going to do is throw in a magnum style PCV grommet that has the smaller hole to see if that fixes that vacuum leak. Worst case, it’s just $6, best case, idle issue is fixed and it costs $6.

Then I’m going to put the carb back to basically how it came off the shelf in terms of jets and bleeds. Gonna put the .070” IABs back in, but leave the .028” IFRs unless you guys think I should go up to a .030-031”.

After that I’m going to pull the initial timing back to 14 degrees just to start, and throw in the moroso weight set I have and start with the heavy springs and map out that timing curve.

In one of those threads linked, TT5.9mag mentions that these engines peak around 3200rpm so it’s good to be all in around that point, and also mentioned that it might be a good idea to have two different springs to bring some advance in early with a lighter spring, and have a heavier spring to delay more advance for a higher rpm. I’m assuming this is so you can have a balance of efficient low rpm cruise without having risk of pinging at the same rpm with a load?

This is my plan, but of course plans can change, so PLEASE give me honest input if I’m going in the wrong direction lol

 

[AJ/FormS]

Humor me;
Back the Idle timing off to 8 degrees,
Set the T-slot to square,
make sure the secondaries are fully closed,
Make sure your Primaries throttle-blades are NOT drilled
Set the mixture screws to 3/4 turn out,
Make sure the WET fuel level is correct and stable,
Flip the PCV out of the grommet, seal both VCs, and
Put the vacuum gauge on the dipstick tube.
DO NOT CHANGE THE SPEED SCREW SETTING.
Start it up and immediately check the vacuum gauge;
If you have vacuum there, your intake gasket is leaking into the valley.
Pressure is normal to see, but do not exceed 4psi, as that can blow seals or gaskets OUT.
If yur normal, then put the PCV back in the grommet and reinstall the breather.
Now, if you still have a high idle; do you have an EGR valve? If yes, then make sure the circuit is not leaking thru the diaphragm, nor sucking exhaust into the plenum.
That's a pretty small cam, I'd idle that down to 600 in gear, up to 700 in N/P.. Even less if you have good hot oil-pressure .
That 650DP is a great carb for your application. It should be snappy as heck.
After you get the idle back to a normal speed, reset your Accelerator pump slack, then check for a tip-in hesitation. If you got one, you gotta fix this before you do anything else. How you do it is to add transfer fuel, while simultaneously subtracting Mixture screw fuel. Just a tiny bit atta time.
After you get that done;
If the Idle speed needs adjusting;
More Idle-Timing will make it run faster,
and less will get you slower.
But more timing with a stock convertor will make it bang into gear. Try to get the rpm DIFFERENCE from in-gear to in-Neutral to less than 150 rpm to prevent the banging.
The higher your Idle-timing gets to be, the more Idle power she will make, and the higher the Idle-rpm will go. Which after 800rpm or so, starts to bang pretty hard on the stock convertor.
There is no good reason to run more idle timing than is absolutely necessary.

After you get the Idle set-up, then begins the task of modifying your Distributor to hit the other targets of;
Power-timing, stall-timing, rate of advance, and cruise-timing.
HappyHotRodding.

 

[jmanhoff]

Humor me;
Back the Idle timing off to 8 degrees,
Set the T-slot to square,
make sure the secondaries are fully closed,
set the mixture screws to 3/4 turn out,
make sure the WET fuel level is correct and stable,
Flip the PCV out of the grommet, seal both VCs, and
Put the vacuum gauge on the dipstick tube.
DO NOT CHANGE THE SPEED SCREW SETTING.
Start it up and immediately check the vacuum gauge;
If you have vacuum there, your intake gasket is leaking into the valley.
Pressure is normal but do not exceed 4psi, as that can blow seals or gaskets OUT.
If yur normal, then put the PCV back in the grommet and reinstall the breather.
Now, if you still have a high idle; do you have an EGR valve? If yes, then make sure the circuit is not leaking thru the diaphragm, nor sucking exhaust into the plenum.
That's a pretty small cam, I'd idle that down to 600 in gear, up to 700 in N/P..
That 650DP is a great carb for your application. It should be snappy as heck.
Industrial Materials & Equipment
After you get the idle back to a normal speed, reset your Accelerator pump slack, then check for a tip-in hesitation. If you got one, you gotta fix this before you do anything else. How you do it is to add transfer fuel, while simultaneously subtracting Mixture screw fuel. Just a tiny bit atta time.
After you get that done;
If the Idle speed needs adjusting;
More Idle-Timing will make it run faster,
and less will get you slower.
But more timing with a stock convertor will make it bang into gear. Try to get the rpm DIFFERENCE from in-gear to in-Neutral to less than 150 rpm to prevent the banging.
The higher your Idle-timing gets to be, the more Idle power she will make, and the higher the Idle-rpm will go. Which after 800rpm or so, starts to bang pretty hard on the stock convertor.
There is no good reason to run more idle timing than is absolutely necessary.

After you get the Idle set-up, then begins the task of modifying your Distributor to hit the other targets of;
Power-timing, stall-timing, rate of advance and cruise-timing.
HappyHotRodding.

I gotta see if I have anything big enough to plug those holes in the VCs, but interesting test that I’ll definitely give a whack. I don’t have any EGR or anything like that, the only vacuum hoses hooked to the carb/intake are pcv, brake booster, vac gauge in the cab, and heater controls.

This is a manual truck, but the same idea applies. 600rpm is a happy idle speed for this engine, even without proper t slot exposure. It has an AX-15 manual trans (v6 Dakota/I6 4.0 jeep 5 speed), with a full size ram flywheel/12 inch clutch so there’s a lot of rotational mass on the crank, it even will idle at 50rpm and continue to run (I’m not joking).

But essentially what you’re saying is after verifying I have no more vacuum leaks, set the t slot square, initial timing at 8 degrees, and 3/4 on the idle screws. Then use the idle timing (to a point) to get the idle speed to around what I want it to be? And then adjust the accel pump accordingly

 

[AJ/FormS]

If you have a manual trans, then the engine is married to the tires and the slowest speed that you can drive at, without slipping the clutch can become an issue. For me, that was at one time, an unacceptable 4.5 mph with 3.55s
Eventually, with a different cam and low-gear combo, I got it down to 3.5 mph @500 rpm.

IIRC, the AX-15 may have a low gear of 3.83, so, this should not be an issue for you.

 

[jmanhoff]

If you have a manual trans, then the engine is married to the tires and the slowest speed that you can drive at, without slipping the clutch can become an issue. For me, that was at one time, an unacceptable 4.5 mph with 3.55s
Eventually, with a different cam and low-gear combo, I got it down to 3.5 mph @500 rpm.

IIRC, the AX-15 may have a low gear of 3.83, so, this should not be an issue for you.

To my knowledge it’s 3.83 in first, with 3.55 gears and 29.5ish tall tires. First is, naturally, very short, but it’s a very snappy truck because it’s so light.