Heat Related Stutter

Ok, I feel really stupid asking this as I like to pride myself on how well I handle problems but I just can't get a handle on this one.

First off, the basics:

My Holley fuel pump flows 80 GPH.
My Performer carb is a 600 CFM unit with .392 jets and the metering rod numbers are 6842.

Accelerator pump is set at the hole closest to the top (least amount of leverage possible any other setting and it gets too much fuel off the line).

When I nail it, she jumps off the line and pulls HARD though first gear, then it hits second and pulls HARD until about 4,000 RPM around then it starts feeling like it's running out of gas. At that point I usually get out of it, today I got out of it then nailed it again at which point it pulled hard again until about 5,000 when I hit 5500 I shifted into third and she started surging.

The reason why I think that it is heat related is because it doesn't do it on the colder mornings after it's had ample time to warm-up (30-45 minutes) and when it's just coming up to temp on the hotter days it doesn't do it but after it gets to 180 it starts doing it and it just gets worse the more I ride around.

I insulated the steel line going from the fuel pump to the carb with a foil backed insulation, no change. The steel line comes out of the pump then runs along the front of the engine and then 90s over the intake to the carb where it goes to rubber line into the carb.

I just can't figure this out short of using a "cool can" the only reason why I haven't made one up yet is because I'm not really sure that it would fix the problem.

Have any of you had a problem like this on hotter afternoons and, if so, how did you fix the problem?

Any suggestions as to how I can keep that damn Mach 1 from embarrassing me after my car gets good and warm? I never can seem to find him when my car ISN'T doing it.

Looking at your signature, a 355 with some goodies and a 600cfm carb. Understand that I'm not picking on anything here, but relating personal experience.

I had a reasonably hot 350 in a Camaro. with a 650 Holley it would stop pulling between 5500 and 6000 rpm. But it was mean as a snake off idle. I stuck an 850 cfm (Holley) on it and you couldn't hardly get it rolling. Totally dead down low. Woke up at 3300 rpm (that's where the cam started to smooth out) and would go right up to 7000 , like right now. I ended up with a 750. Had enough flow at low speed to keep a tiny bit of torque and was big nough to make some power at higher RPM.

I would suggest that you try a little more carb and see if that fixes your problem. It may be as simple as it's running out of air at higher RPM. And only when it's hot, the air density will be lower. Hot air is thin compared to cold.

Suging is usually caused by a lean condition. Jerking is too much advance.
I would verify 36* total mech timing, then verify you have no more than 52* total.
You might back off 2* and try that.
If that is fine, check for low float level,vacuum leak,EGR valve stuck,etc.
Vapor problems are usually on the suction side of pump, not the pressure side.
My 2 cents

It was doing this last summer when it had the .400 jets in it and was leaving black marks in the driveway under the exhaust pipes in the mornings and leaving a "haze" behind me when I went WOT.

I have verified the timing but I still don't have the correct vacuum pot, it should be in NEXT Friday :banghead: anyway, it's done this with very conservative timing (28 total mech.)

I would figure that a vacuum leak would rear it's ugly head at all times, not just when it's hot wouldn't it?

I'm not 100% on the float level (Carter AFB style carb.) but it works perfectly on the colder days.

No EGR.

That's the problem, everything that I can think of, doesn't work, I guess I'll have to buy a length of fuel hose and rig up an impromptu "cool can" and see if that works, I'd hate to have to buy a bigger carb, just seems like a waste of money, a 600 SHOULD feed up to 400 horses shouldn't it?

28* is way too low. Try 34* at 3,000 RPM. What kind of dizzy?

CIDXRPM/3456XVolumetric eff.+CFM

EX:350CIX7,000RPM/3456X100%=709CFM

With that high volume pump, it's not hot fuel. Check the float adjustment.

(I am moving this to tuning)

It's basically a stock HEI unit with a supercoil (I know that doesn't really matter I just added that for clarity).

How would I adjust the float level on a Carter AFB (Edelbrock Performer, manual choke) carb? I was thinking that it was possibly a "stuck float" or something like that but I haven't found where to adjust it.

So a 750 CFM carb would be better?

First thing I would do is buy a Mr Gasket 928G spring set. Install the 2 gold springs, then set to 34-36* total mech at 3,000 RPM. That will wake her right up.

You have to pull the airhorn to set the float level. Need instructions?

big2bird said:

First thing I would do is buy a Mr Gasket 928G spring set. Install the 2 gold springs, then set to 34-36* total mech at 3,000 RPM. That will wake her right up.

You have to pull the airhorn to set the float level. Need instructions?

Click to expand...

Yeah kinda, basically all I've ever done was replace metering rods and springs along with the jets, I also removed the choke completely, makes it kind of a PITA in the mornings but that's how I wake-up.:huh:

It has the Mr. Gasket weights and one gold spring with one medium spring, first thing tomorrow it will have two gold springs, it has plenty off the line and through first gear, it just feels like it's not getting fuel after that on the hot days, she runs strong all day long on cool overcast days. I'm so confused.

http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf

This will help

SmokeyVette said:

Yeah kinda, basically all I've ever done was replace metering rods and springs along with the jets, I also removed the choke completely, makes it kind of a PITA in the mornings but that's how I wake-up.:huh:

It has the Mr. Gasket weights and one gold spring with one medium spring, first thing tomorrow it will have two gold springs, it has plenty off the line and through first gear, it just feels like it's not getting fuel after that on the hot days, she runs strong all day long on cool overcast days. I'm so confused.

Click to expand...

Do you have the old GM weights? If so, use them with 2 gold springs. Aftermarket weights SUCK.

Sweet, I will, I hardly ever throw away car parts, I still have the old shift kit that was in my 700-R4 along with the 2-4 band that it broke.:bonkers:

If you changed weights because your bushings were worn, NAPA has them.

It's still doing it, the hotter it gets the worse it gets, so I'm going to rig up a "cool can" and see if that helps. That's the only thing I can think of to fix it.

I still don't believe that is it. How about more info?
1)Timing good now?
2)Gasket type?
3)Heat shield?
4)Exhaust crossover open?
5)Restrictors in there?
6)Choke type

I am thinking since you have a heat related lean, the fuel bowl, not the feed is hot. Maybe an insulated 1/2" base gasket is more helpfull.

Timing is dead-nuts on except for the vacuum pot.
Gasket? Carb gasket? It's not one of the thick ones it's just a regular piece of gasket material about as thick as a fuel pump gasket.

Heat Shield???? No, I can't mount anything under the carb, the breather touches the bottom of the hood at WOT as it is.

Headers, no exhaust crossover, I don't believe I've ever heard of an exhaust crossover.

Restrictors? Please elaborate. Are you saying that I need some or if there are any?

Choke type? None. Absolutely zero, no choke plate, linkage, nada (it did this before I removed the choke)

I'll try and see if I can fit a thick carb spacer under there but I doubt it.

I'm going to try out a rudamentary cool can tomorrow, along with jetting my secondaries rich to see if that will help, a hot fuel bowl WOULD explain it though...hmmm:suspicious:

That perfomer manifold has an exhaust crossover built in under the plenum. I would block it off.
Later quads had a 3/8" thick insulated carb gasket to prevent fuel bowl heat. I will post a picture later.
Headers? Your new fuel pump has no return line huh? I bet the old one did. Did you have this problem with the old pump? If the headers are close to the tank line................



The one on the right is an insulating type carb base gasket.

See that's what I was thinking, maybe the headers are heating up the fuel before it gets to the pump.

You are absolutely correct about the return line, would running a return line help?

Anyway, I tried taking the thick gasket off my Nova to put on the 'vette to try it out before I actually went and bought one (the Turtle in me) but forgot that the Nova was spread-bore Quad, and the 'vette isn't. I could changed the studs to the other holes but then I'd have to revamp everything so I think I'm just going to buy one.

Where would this exhaust crossover be? Would I have to pull the intake to block it off? I bought this manifold off of a bracket racer who ran 7's in the 1/8 so I would naturally assume that he had already blocked it off, but since he only ran his car 1/8 mile at a time...he probably didn't.

I should've caught that the exhaust crossover was under the plenum.

No, I took a look at the headers they only get within about 4" of the fuel lines and that is where the fuel lines are on top of the frame rail so I'd assume that the frame rail would act as a heat shield of sorts.

I would like to take this time to tell you that I really appreciate all of your help so far and I'm sure you've got it narrowed down to a hot fuel bowl, the reason I think so is because when I went to check the fuel filter, the moment that the gasoline hit the intake half of it boiled away.

I will be getting a 3/8" carb gasket and GOD I HOPE THAT FIXES IT!:suicide:

The exhaust crossover provides a path for exhaust during heat riser operation, a route to the EGR, and heat for a divorced choke. If I lived in Texas, or out here for that matter, I block them off whenever smog laws allow.
Keeps the carb cooler, and the air/fuel charge cooler.
You will have to remove the manifold to do that though. New Fel Pro gaskets, RTV on the China walls, and some SS material to block the exhaust passage.

I had a fuel perkolating problem. I installed the shield that you see in this pic. Stopped the perk problem. It is pretty thin and sandwiched between 2 gaskets.