Cookwithvette

I've only ever driven modern EFI cars during the winter and this recent cold snap is giving me some real issues with the Corvette.

Until the temp has reached 180 it threatens to stall at lower rpms. An example... I come to a stop but keep the gas on a little to keep it from stalling. When I go to accellerate it might cut out for a moment and then begin to go normally or stall completely. Sometimes it REALLY doesn't want to move from a stop but will go sputtering and coughing.

Even when the car has warmed up it doesn't drive quite right. Tonight I tried to pass somebody. In second gear I smacked the throttle down and the engine just about quit. After a second or two of hesitation it roared back and I shot up to 5000 rpms without a problem. (Aside from scaring the hell out of me.)

All of this has just come about with the cold weather.

The mechanic who installed the engine used a resistor on the electic choke but I could swear the choke is supposed to get a full 12 volts. Could the choke be staying shut? I haven't been able to get under the hood lately but I have tomorrow off and would really like to solve this.

Cookwithvette

ttt

page62

Find another mechanic who really understands how to adjust carbs in general and chokes in particular. They're out there -- generally they have to be at least 40 years old!

Your choke is improperly set up, but there may be some general setup issues, too.

Cookwithvette

When I get the new carb I'll have somone dial it in.

Should I really just be able to start it and go like during the summer?



[Modified by Cookwithvette, 3:44 AM 10/16/2002]

Cookwithvette

I checked things out today. Choke is opening in about one minute. It is opening completely. I richened the idle mixture on all four screws and she's running a little better but then again it was warmer today.

page62

You should be able to come close to "start it and go." But I don't even do that in the summer. From a cold start, I need at least 15-30 seconds of warmup time before I put it in gear.

Perhaps an expert (not me) can tell you how long that choke should stay closed...

Twin_Turbo

Is the thermac system working?

Jughead

I've lived in Western PA my entire life and one of my first cars was a 1967 Formula 400 which I drove year round---I was a 'po boy back then(1970). :D I also had a brand new 1976 455-TA but I never had any of the above symptoms you've described merely due to a "cold-snap" It does sound live you have carb-choke-and maybe vacuum issues.

Back in the 60's we didn't fully warm the engine up before driving---heck we usually drove off in the first 20 seconds after starting. And that was with a 335HP 400ci Poncho. Unless the temp was in the teens, I usually started the engine, waited until it stabilized and then drove off.

I remember my dad back then always complaning about the choke, float and other carb problems with his cars--he was always fixing something.

Just because your choke is opening properly doesn't mean it's remaining open. I've had both an Edelbrock and Holley with choke problem. I could never get them set properly and they seemed to have a mind of their own. The Edelbrock also would never keep a set idle. I also had a 750 Holley with a manual choke in which the choke would mysteriously close---in traffic!!!

Do you have a manual for your carb? Once warmed to 180 you should ideally have no carb, choke or drivabilty issues. Heck, by 120 you should be fine.

Paul G

You are experiencing one of the most frustrating problems you can get with a carbed engine. The choke seems to me like it is opening to soon. That will cause a lean condition during warm up and the engine will run like crap. Getting that set right is a bear. If they can get it adjusted so to not let the engine die out during warm up you will be lucky. There is a choke pull off which is vacuum operated. It's job is to pull the butterfly open just a fraction of an inch while the choke is still trying to hold the butterfly closed. If the pull off is pulling the butterfly too far open it will hesitate and want to stall out. Likewise it will hesitate and have no power if the pull off is not opening enough. Getting the choke adjusted properly is an art. It takes a lot of trial end error.

Fuel injection solved all of those problems, and created all new ones. :smash:

Good luck.

vettfixr

If your choke is opening all the way in 1 minute it's opening way too soon. Doesn't the demon carb have an adjustment on the choke to run rich or lean (longer or shorter)? If it does you can try moving it one notch richer at a time until you get the driveability you want. If you're getting better cold start driveability by adjusting the idle mixture you are probably running too rich when the car is warmed up. Hope this helps a little.

Cookwithvette

I'm going to remove the resistor and crank the choke timing down until it stays closed for about 1:30-2:00 @ 45 degrees.

Generally I would start it and wait a minute or so before trying to drive it but today I tried waiting only 30 seconds and it seemed to like that just fine. But today was in the high 40s.

I don't have a thermac. I have headers and one of those goofy Edelbrock triangular air filters. I'm looking to get something better but hood clearance is REAL tight. Also, thanks to the headers I don't have an EFE valve.

I can't wait until I can afford a fuel injection setup.


Thank you all very much. I really appreciate it. :cheers:

Apeiron

Your choke probably doesn't need a resistor, but in any case removing it will probably make the choke open faster.

Green76

Cookwithvette,

I see you have a ZZ4 in your vette, the problem with that motor is it has no exhaust crossover in the intake manifold and cylinder heads, that is going to be a problem when it gets cold outside.
Ajusting the choke and idle mixture screws might help a little bit also changing the thermostat to a 192 - 195 deg. might help.
I have similar problems with my vette untill it is fully warmed up, I'm using a Q-jet carb with elecrtic choke and no resistor.
Ulf

Cookwithvette

I finally found the demon manual and it puts emphasis on having 12 volts at the choke so the resistor shouldn't be there. I know it will make it open faster but you can rotate the pod to adjust the timing. I'll just crank that down. At least if its getting 12 volts it shouldn't close while driving.

No exhaust crossover? I had assumed everything except race products had the crossover. Even the heads too. Sheesh. So changing to the performer 21011 manifold with a crossover wouldn't help. Why does the ZZ4 manifold have a plate covering where the egr valve would be though?

I actually have a 195 stat kicking around. Maybe I'll pop that in.