Thread: Rochester 2bbl Carb on 350 Hesistation/Stall long warm up ?

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Hey Guys I have a problem that I am not sure what is going on. Here is what is happening. It has a Chevrolet 350 stock crate engine with 400 Turbo hyd. trans. It has a Rochester 2bbl carb on it. I am pretty sure it is a reman from Autozone (judging from the part # on the sticker on it plus it says Reman on it). I didn't put it on. It came with the car when I purchased it and was already installed. It appears to be a year or so old. It has had this problem since I have owned this car. Anyway, I have noticed that when cold or even slightly warm my car studders(hesitates and wants to stall) when backing out of my driveway. I can even let the coolant temp get up to 175F and it still does this. It attempts to stall. Now if I push the gas harder it seems to all of a sudden get power and back out of the driveway fine. Also, if I start driving it with the coolant temp around 175-180F there seems to be this studder/hesistation while lightly getting on the gas or going up a small grade. If I push the gas harder it gets up and goes without hesistation. I have had other carbs cars in the past and I could fire them up and leave my driveway in a minute or two. On this car I have to let it warm up for at least 5 minutes before I can get out. Now the outside temp today was 88 deg. F. So it isn't cold by any stretch. This is a custom application so telling you the make or model won't help as it wasn't OEM. Here are the part #s on the carb.

GM 2 Jet BC (on top)

On side: 17057110

0187 AMM

On Front: 11-09-99-05

Part# 3-735 (Auto Zone Reman. Champion Carb #)



What do you guys think is going on? What should I do to try to fix this problem. Maybe it is jetted for economy? It still looks new and doesn't leak. I just would like to be able to get out of the driveway without waiting 5-10 minutes for it to warm up to 195 deg F coolant temp plus I don't like the hesitation when driving with light throttle when cold as it attempts to stall if I don't give it more gas. Now once the car is up to operating temp the car runs great with no hesistation or bogging of any kind. Idle is steady and strong. I just went through the ignition thoroughly. My plugs are a very nice toasty brown. I have a electric choke that is working. Any info would be appreciated. Thanks for your time.

Sounds like the choke is coming off to early.

The float might be set too low. Its leaning out, anyway. Is the accelerator pump giving a shot as soon as the throttle begins to open? If not, it will starve the engine off idle.

Hi guys. I am still fighting this problem. Here are the items that I checked/tried. I adjusted the choke and made sure that the butterfly closes properly. It didn't really help. I tried different adjustments just to see what the differences are but it didn't help. I checked to make sure that the accel. pump squirts gas into the carb. Every time I pulled the throttle is squirted a small stream of fuel. I also started the car and watched the choke butterfly to make sure it stayed closed after the engine started. It did and then after a few minutes gradually started to open. Then I tapped the gas and it came off of high idle and the choke opened completely. (same rod as my fast idle cam) Just for background this is an aftermarket electric choke with the sensor that bolts to the valve cover. I didn't install it. It came with the car. Please let me know if I did something wrong.

Now here are a few more things I noticed. The engine's coolant temp was around 170F and I let the car run/idle for about 8-10 minutes before driving. I drove down the road. The throttle was fairly smooth until one point and then it felt like the carb was trying to make a transition but it was having trouble. The car almost had a large bog at this certain point. It didn't want to take more gas unless I pushed it down quite a bit more. More than I would during normal driving. I drove around for a few minutes and I noticed it also when I started to go up a hill. Everything was smooth then I started climbing the hill and then about halfway up with no adding much more throttle it started to bog then I gave it more gas and it was fine and went right up the hill.

Now after it warms up everything is as smooth as one could hope for. There is no hesistation or bog. Also, if I just let it idle and warm up sitting in the driveway without driving it, it will run great too. However, the coolant temp seems to like to get up to 185-190 before that bog/hesitation goes away. I am not sure what is going on. It has the same problem in reverse as well going out of my driveway. I will give it gas and hold the throttle fairly still. Once I get to a certain point on the driveway it will start to slow down and want to stall. If I give it just a little more gas it will stall but if I give it 1/4 more throttle it shoots me right out of the driveway with no problem. Also if the car is warm it can crawl right out of the driveway without hesitation.

I talked to Joe at CarbUSA and he was kind enough to spend sometime discussing this with me. He thought it sounded like a choke issue as well. I did everything he asked me too and I tested everything he asked me too and I still can't find the problem.
Could the problem be in a transition circuit in the carb? Guys I would appreciate any info on this. I am very pleased with the way my car runs except for this problem. For many of us car guys that is very rare. Normally, you have a to do list or things you want to do to get your car just the way you like it. I just have to figure out what is causing this. Please let me know any ideas you guys may have. I will be glad to try them. I thought I might be down a cylinder or ?. I checked for spark on all cylinders. I removed one plug wire at a time to make sure the rpms dropped equally. I have all new plugs, and wires. Checked the idle speed and timing. Like I said I couldn't ask for the car to run better when warm. I drove over 40 miles the past couple of days up hills and around without any problems except when it is warming up or not up to 185F. Thanks.

Originally posted by DennyW
Try one notch richer on the choke stat. What you seem to need is more choke time. The pull-off adjustment should remain the same. Just change the choke setting first. Base settings for that carb by number call for Index (neutral, not rich, not lean).

Oh, and don't tighten the air cleaner nut to tight, as it can bend the air horn (top of carb).

hey denny, the choke pull off could be pulling it off to much to start with and that could cause his problem also. adj. the pull off rod longer.

Thanks guys. I appreciate all of the info. I am sure the problem happens when it is cold as well. I just haven't tried to drive the car with the coolant temp at or below 160F as I know it would stall or bog badly.
After speaking with Joe at CarbUSA the other day I tried moving the dial back a few notches. It was on the second to last notch on the right side. I moved it back to the center notch. It still had the problem. He also mentioned that I shouldn't see anything when the choke is closed. It should be closed completely. So I moved it back another few notches then when the car would start it would immediately stall. So, I put it back to the center notch.

I know what you mean about the bolt. I had my air cleaner off and I saw that it was close to the choke. I was excited as I thought this might be my problem. I unscrewed it some but it didn't make a difference.
It must be a choke problem. Everyone seems to think it is so I will keep focusing my attention there. I read through my Rochester book but it didn't help me out too much as far as fixing the problem.

I would like to see pics. My carb experience is limited to Webers pretty much. I have rebuilt some models and understand how they work but they add fuel vs. restrict air for the choke. So, this type of system is new to me. I can also take some pics of my carb and how it is setup. Maybe that will help.
From what I can see when the high idle comes down the choke butterfly has to open. It has one rod that connects to the electric choke then it goes up to the choke butterfly, then from the butterfly on the other side of the carb it connects to another rod that connects to the fast idle cam/idle adjustment screw.

I am sorry but I am not sure how to check many of the adjustments you showed below. If there is any info that I can provide to help please let me know. I will galdly try to answer any ?'s. Thanks Again.

Just a thought, but something I've seen several times. Grab the top of the carb, and try to twist it back and forth while watching the base/main body of the carb.

In a some cases, the screws holding the base to the body of the carb work loose creating small vacume leaks and weird symptoms. Generally if it's not too loose, it will get better as the car warms and the metal expands.

Might be worth a look.

Thanks guys. Great info on the autozone website. That looks like the same carb I have. I will go out soon and gets pics of the carb. I will also try rotating the carb like Mike P said. That is a great idea. Thanks Again guys and check back soon for the pics.

Ok here are some pics of the carb and linkages. I took some with the choke closed after I pushed the throttle once when cold. I also took a close up of the fast idle cam. Thanks.

Choke pic. Outside temp is 70F right now.

Choke closed after pushing the throttle down once.

Fast idle cam when choke is set.

Idle cam when in regular operating temp idle.

Top view of carb and linkages.

Originally posted by Greg
Idle cam when in regular operating temp idle.

the idle cam shouldnt be hitting the idle screw now. the cam should be all the way off. it should be idled up to hi there. dont have anything to do with your problem though. you didnt show how much the choke pull-off opens the choke when you start the motor cold. some good pic.