Warm Engine Idle Issue

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T-Port sync
You have too much Idle timing, so the mixture screws are turned out too far and the transfers are almost closed. It will idle this way, but the transfers stop flowing and dry up. Then when you touch the gaspedal, the transfers have to start up again.And then you get a hesitation. Between that and the low cylinder pressure,(maybe 8.5 or so) it's a doubly whammy tuning issue.
The fuel pump, if deadheading,is putting the pressure on the float valves, so maybe the level creeps, and the idle gets richer and richer.
I suggest
Carb Tunning

I know you said the speed screw was set to be "still on the idle circuit", But that can mean almost anything. With that cam,you want the T-Port exposure to be about square.The mixture screws out around 1Turn from lightly seated, and the idle timing down at 12ish. Idle should come in around 650 in gear, maybe up to 700, but the neutral should not go over 750. All this once the tune is in and no vacuum leaks, including not sucking air from the crankcase. Make sure the plugs are hot enough.I think 68s are too big on the front, but that should not affect the idle one bit. That cam should idle higher than 11@800, oops sorry, you said in drive. Check it in neutral after the changes are made.
Yeah I'm guessing,lol.
Humor me........

That cam installed at 106 per directions, puts your ICA at 60*, and with 8.5SCR, the Dcr is 7.00,dare I say it; kindof low, so the tune will need to be dead on for it to be FUN!
That Stealth 8022 IIRC is a big-port intake, while an excellent manifold, it is too much for your combo. With the small-port heads and 8.5Scr, a smallport dualplane will make the engine much more responsive.The lack of air-velocity through it at idle may also be a contributor, to both the high idle requirement and the hesitation.
 
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AJ/FormS said:
T-Port sync
You have too much Idle timing, so the mixture screws are turned out too far and the transfers are almost closed. It will idle this way, but the transfers stop flowing and dry up. Then when you touch the gaspedal, the transfers have to start up again.And then you get a hesitation. Between that and the low cylinder pressure,(maybe 8.5 or so) it's a doubly whammy tuning issue.
The fuel pump, if deadheading,is putting the pressure on the float valves, so maybe the level creeps, and the idle gets richer and richer.
I suggest
Carb Tunning

I know you said the speed screw was set to be "still on the idle circuit", But that can mean almost anything. With that cam,you want the T-Port exposure to be about square.The mixture screws out around 1Turn from lightly seated, and the idle timing down at 12ish. Idle should come in around 650 in gear, maybe up to 700, but the neutral should not go over 750. All this once the tune is in and no vacuum leaks, including not sucking air from the crankcase. Make sure the plugs are hot enough.I think 68s are too big on the front, but that should not affect the idle one bit. That cam should idle higher than 11@800, oops sorry, you said in drive. Check it in neutral after the changes are made.
Yeah I'm guessing,lol.
Humor me........

That cam installed at 106 per directions, puts your ICA at 60*, and with 8.5SCR, the Dcr is 7.00,dare I say it; kindof low, so the tune will need to be dead on for it to be FUN!
That Stealth 8022 IIRC is a big-port intake, while an excellent manifold, it is too much for your combo. With the small-port heads and 8.5Scr, a smallport dualplane will make the engine much more responsive.The lack of air-velocity through it at idle may also be a contributor, to both the high idle requirement and the hesitation.
Click to expand...
Thanks for taking the time to write all that down. I'll pull the carb and check those slots. I'll also try adjusting the timing and idle RPM. Looks like we are going to get some rain here, so it may be a while. Car is outdoors.
 
I would recommend that you go a little higher. One thing to keep in mind is that a pop thru the carb can take out the power valve, especially if the carburetor doesn't have a check valve to protect it. A blown power valve will cause a rough idle.
 


The best way to set power valve opening is by measuring intake vacuum at a cruise. Not idle. What ever cruise vacuum is, make the PV open 3-4 inches later. For example, if you cruise at 16 inches, a 10.5 PV is what I'd use. You will probably be able to pull one or two main jet sizes out when you get the PV opening at the right time.


To test the fact that the PV does zero at idle, just take it out. It will not affect idle one bit. You can take the main jets out as well and it won't affect idle.

So set PV open to cruise vacuum not idle vacuum.
 
yellow rose said:
The best way to set power valve opening is by measuring intake vacuum at a cruise. Not idle. What ever cruise vacuum is, make the PV open 3-4 inches later. For example, if you cruise at 16 inches, a 10.5 PV is what I'd use. You will probably be able to pull one or two main jet sizes out when you get the PV opening at the right time.
Click to expand...

In your example, the difference is 5.5", but you say 3-4. Which one is it?
 
He said what he said because they don't make higher than a 10.5 pv.lol

That's one way of doing it, I usually just start by leaning the jets out till I get a slight surge at cruise or about 50 mph...then jet back up 2 jet sizes. With auto trans cars i do the half of vacuum loaded/in gear or even one size over half of vac loaded/in gear
 
mopowers said:
In your example, the difference is 5.5", but you say 3-4. Which one is it?
Click to expand...


I should have pointed out that's all you could get. Back in the day, they made a 12.5 PV and I used a bunch of them.

So, I'll say 3-4 inches lower than cruise if you can get the PV, if not it is a 10.5 because that's what you can get.

Example B might have 13 inches of cruise vacuum so a 10.5 would work. Next up would be an 8.5 because I don't think they make a 9.5 PV. It's all about getting the PV as close as you can to cruise vacuum so it opens at the right time. If your cruising at 16 inches and have a 4.5 PV the engine will think it's waiting all day for the extra load fuel.
 
With manual trans I use a pv 2" below vac @idle. The vacuum drops in a blink when you dip the pedal, as long as the pump shot is right , the power valve can be close or within one size of best 'say one higher' and really not give you any grief.
The further south you go from the correct size power valve... stumble will occur.
 
I got a chance to wrench on the carb tonight before it started to rain. I verified the transfer slots on my primaries were way too open, about a 1/4 inch. I squared them off as well as the secondary slots as per Holley tech support and it was running way too lean that I had to have the mixture screws out 3-4 turns for it to run good. Shut the secondaries closed like it came from the factory and it ran much better, but had two have the primary transfer slots open about the size of two squares. I noticed something new tonight though. When I turn on the headlights on, especially the high beams or turned the AC on while the engine was acting up, it magnified the stumble and the engine would die. Do you think the alternator, voltage regulator, or battery could be causing this problem? It will be a couple of days before I can get back on the car, so plenty of time to come up with a plan of attack. Thanks everyone!
 
73Swinger18 said:
I got a chance to wrench on the carb tonight before it started to rain. I verified the transfer slots on my primaries were way too open, about a 1/4 inch. I squared them off as well as the secondary slots as per Holley tech support and it was running way too lean that I had to have the mixture screws out 3-4 turns for it to run good. Shut the secondaries closed like it came from the factory and it ran much better, but had two have the primary transfer slots open about the size of two squares. I noticed something new tonight though. When I turn on the headlights on, especially the high beams or turned the AC on while the engine was acting up, it magnified the stumble and the engine would die. Do you think the alternator, voltage regulator, or battery could be causing this problem? It will be a couple of days before I can get back on the car, so plenty of time to come up with a plan of attack. Thanks everyone!
Click to expand...



What RPM is it idling at? When you load the electrical system at low speeds the alternator may not keep up. I'm not an electric guy but I know the system will run the lights before it fires a plug.

Also, if you have the screws out 3-4 turns you either need a smaller idle air bleed or a bigger idle feed restriction.
 
yellow rose said:
What RPM is it idling at? When you load the electrical system at low speeds the alternator may not keep up. I'm not an electric guy but I know the system will run the lights before it fires a plug.

Also, if you have the screws out 3-4 turns you either need a smaller idle air bleed or a bigger idle feed restriction.
Click to expand...
I had it set around 750 at the time. Even when I raised the idle to 900, it did the same thing. I only had to keep the screws out 3-4 turns when I opened up the secondaries exposing the transfer slots. Called Holley again today and they said to leave them closed. It runs best this way anyways. We have some rain scheduled here, so while waiting to work on it again I ordered a 4 hole carb spacer in hopes to increase the signal a bit and improve the idle.
 
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Maybe a long shot, but makes sense to me. What if the voltage regulator which is mounted on the firewall in close proximity to the headers is getting too hot and reducing the voltage output. Below is the chart from the manual showing how it decreases voltage with an increase in ambient temp. I'm pretty sure it's well over 140F. Thinking about getting the engine to duplicate the gripe and then shutting it down quickly and piggy backing another regulator in and firing it back up to see if it fixes it. The AC and lights work fine until it gets hot and the engine starts to do it's thing.
regulator.jpg
 
So you are using an 1850 Holley?

IIRC that thing has a 28 squirter in it.

If so, go up to a 35 and use the pink cam and put it in the number 2 hole. It may just be a squirted issue.
 
It came with a 31 installed and I verified the accelerator pump with a feeler gauge. It squirts the instant you touch the throttle. I think it came with the red came and already had the screw in the number 2 hole. I should receive a 1/2" 4 hole phenolic carb spacer I ordered tomorrow to replace the divided heat insulated base gasket from Edelbrock that is currently installed in hopes to increase the vacuum signal at the base of the carb. We shall see. Also, I pulled all the spark plug wires I installed just a few months ago and found two of them to have a couple hundred ohm variance when manipulating them. I'll change them just to be sure. AJ recommended installing a PCV valve to increase the air intake, so I'll try that too. If none of this helps, I am going to find someone around here with a Sun Scope Analyzer. That should help me rule out a few things.
Speaking of which, there is one near me on Craigslist...
Sun 740 Electronic Engine Tester Scope
 
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Where is the cam installed? That's a big cam for a 318. It should be installed advanced pretty good with stock compression. More than the 4* that Comp says. Your cranking compression sucks dead camel balls at 135. This is why you have to pull in so much initial timing. Just kinda spitballin.
 
RustyRatRod said:
Where is the cam installed? That's a big cam for a 318. It should be installed advanced pretty good with stock compression. More than the 4* that Comp says. Your cranking compression sucks dead camel balls at 135. This is why you have to pull in so much initial timing. Just kinda spitballin.
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Heh heh , yeah that's not helping is it...and I would have used a 4 corner idle with that cam 600 dbl pump. He could drill the butterflys so he can get the throttle blade where it needs to be if he wants.
 
Rusty, sorry I didn't see your post. I blocked you after the lack of tact you displayed in my post asking questions about leaf springs and several other users questions. Feel free to continue replying to my threads, but I wont see them.
 
Not to argue, but
My old 750DP has no 4 corner idle, and it worked fine on my 292/508/108 purple cam, with just a bit of secondary cracking. I tried drilling the plates, increasing the hole-size in small steps,and closing up those secondaries, and after a bit,it ran about the same.
The same carb/same engine, but with a 270/280/110 Hughes cam; well she liked the secondaries shut up tight, and I had to close those pesky holes.
The same carb/same engine but now with a 276/286/110 Hughes cam, the carb is exactly the same with just a tiny bit of secondary cracking.
All three cams were initially set up with timing in the range of 12 to 16 degrees.I currently run 14*, with the 276 cam.
I tried a 750 Vacuum secondary, but I couldn't wait for the secondaries to open; I'm impatient that way,lol. With the DP I can stomp it at pretty much any speed below 55 at almost any reasonable rpm, and light up the tires.The Vsec wouldn't do that, no matter what spring was in there.I like tirespin!
I also tried a 600Vsec.As compared to the 750 DP,that was like loosing two cylinders.The only good thing I can say about that bad-boy, is that it is possible to lean it out pretty far and get some really fantastic miles per gallon,lol.
But,I think my cylinder pressure is up around 175psi(aluminum heads)

And I've never had a teener, with a 268, and 135.
Unless you include the 340 cam, and
that combo, with the 340 heads,intake,and TQ carb, did "suck dead camel balls", to be sure.
 
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AJ/FormS said:
Not to argue, but
My old 750DP has no 4 corner idle, and it worked fine on my 292/508/108 purple cam, with just a bit of secondary cracking. I tried drilling the plates, increasing the hole-size in small steps,and closing up those secondaries, and after a bit,it ran about the same.
The same carb/same engine, but with a 270/280/110 Hughes cam; well she liked the secondaries shut up tight, and I had to close those pesky holes.
The same carb/same engine but now with a 276/286/110 Hughes cam, the carb is exactly the same with just a tiny bit of secondary cracking.
All three cams were initially set up with timing in the range of 12 to 16 degrees.I currently run 14*, with the 276 cam.
I tried a 750 Vacuum secondary, but I couldn't wait for the secondaries to open; I'm impatient that way,lol. With the DP I can stomp it at pretty much any speed below 55 at almost any reasonable rpm, and light up the tires.The Vsec wouldn't do that, no matter what spring was in there.I like tirespin!
I also tried a 600Vsec.As compared to the 750 DP,that was like loosing two cylinders.The only good thing I can say about that bad-boy, is that it is possible to lean it out pretty far and get some really fantastic miles per gallon,lol.
But,I think my cylinder pressure is up around 175psi(aluminum heads)
Click to expand...
To the first thing you said, that is a bit larger venturi and I'm sure it helps with high enough initial timing to boot, prabably 2-3 turns out on the idle screws. Crazy but look at the vac secondaries bores for transfer slots sometime.
 
It's fixed, for real this time. Unfortunately I can't pinpoint exactly what the fix was due to all the stuff I threw at it while I had the chance. Below is what I did.

- New plugs/wires. Really don't think anything was wrong with the originals.
- Pulled carb and adjusted transfer slots square.
- Installed a fuel return line using a 3 way filter and the tank vent line that runs up to the engine bay as my return. Have a vented tank cap.
- New gas tank and filter sock. The filter was disintegrated.
- Blew out return and supply lines with compressed air and changed all rubber hoses.
- Cleaned the fuel pickup assembly tube with a 22LR barrel brush and snake since it was corroded.
- Insulated all fuel lines in the engine bay.
- Installed a Holley carb heat shield and gasket.
- Installed a 195 deg thermostat. Had a 180 in there before.
- Installed PCV valve. Two breathers before.

Thank you everyone for all your help and suggestions!
 
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