Cold weather idle/running issues.

[Honky Kong jr]

Now you've said it...lmao my previous cars have never done this in cold weather but it's been fuel induction. So you think maybe I should just let it be till the weather passes or do I have a problem I need to be looking into?

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If it’s the choke it probably isn’t working properly at anytime, you just don’t notice it because in warmer temps cold start is so dependent on the choke.

 

[deve05]

If it’s the choke it probably isn’t working properly at anytime, you just don’t notice it because in warmer temps cold start is so dependent on the choke.

Damn dude.... Uuhhmmm... You can laugh at me if you want... I prolly deserve it cuz im blind when it comes to carbs.. as a tech all I've ever done is fuel injection and by the time i was born carbs were gone lol anyway... My truck doesnt have a thermostat in it... So it never warms up past the first line on the temp gauge. Annndddd here's my next thing... Im gonna go mess with my carburetor tomorrow. I know the bare basics like idle speed adjustment and the two adjustments for rich/lean, and i know the choke has an adjustment on it where you can loosen two screws and spin it. So tomorrow when i mess with my carb, what should i be looking for? And can the choke be fixed without tearing the carburetor apart?

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[Honky Kong jr]

Damn dude.... Uuhhmmm... You can laugh at me if you want... I prolly deserve it cuz im blind when it comes to carbs.. as a tech all I've ever done is fuel injection and by the time i was born carbs were gone lol anyway... My truck doesnt have a thermostat in it... So it never warms up past the first line on the temp gauge. Annndddd here's my next thing... Im gonna go mess with my carburetor tomorrow. I know the bare basics like idle speed adjustment and the two adjustments for rich/lean, and i know the choke has an adjustment on it where you can loosen two screws and spin it. So tomorrow when i mess with my carb, what should i be looking for? And can the choke be fixed without tearing the carburetor apart?

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I really don’t mess with slobberjets but I will tag someone to your thread who does. I throw them away lol @1987 GMC Jimmy

 

[75gmck25]

Take off the top of the air cleaner so that you can see the carburetor venturi.

With the engine cold, push down on the accelerator or manually move the linkage so that it sets the choke, and you should see the choke flapper on top go shut. Then start the truck, hold the accelerator down until it will run on its own, and let it idle. The choke flapper should have popped open slightly because of the vacuum choke pull-off.

Once it starts to warm up, the choke flapper should gradually open further. However, this only happens if there is 12 volts applied to the choke so that it heats up the mechanism and the spring inside unwinds. Once the engine is warm, push the accelerator down slightly again and see if it takes pressure off the choke linkage and lets it pop fully open. If the choke plate does not go fully open (straight up and down) with a warm engine, then the choke is not working or is not adjusted right.

A standard Quadrajet or Edelbrock electric choke has a round black mechanism with three screws around the edge. On the top edge of the black housing there should be 3-4 index marks, and a mark on the choke body. If you loosen the screws it will allow you to rotate the choke housing and adjust it to richer (more closed) or leaner (less closed). However, you still need 12 volts to make it work correctly.

Bruce

 

[Honky Kong jr]

Rock on @75gmck25

 

[deve05]

Take off the top of the air cleaner so that you can see the carburetor venturi.

With the engine cold, push down on the accelerator or manually move the linkage so that it sets the choke, and you should see the choke flapper on top go shut. Then start the truck, hold the accelerator down until it will run on its own, and let it idle. The choke flapper should have popped open slightly because of the vacuum choke pull-off.

Once it starts to warm up, the choke flapper should gradually open further. However, this only happens if there is 12 volts applied to the choke so that it heats up the mechanism and the spring inside unwinds. Once the engine is warm, push the accelerator down slightly again and see if it takes pressure off the choke linkage and lets it pop fully open. If the choke plate does not go fully open (straight up and down) with a warm engine, then the choke is not working or is not adjusted right.

A standard Quadrajet or Edelbrock electric choke has a round black mechanism with three screws around the edge. On the top edge of the black housing there should be 3-4 index marks, and a mark on the choke body. If you loosen the screws it will allow you to rotate the choke housing and adjust it to richer (more closed) or leaner (less closed). However, you still need 12 volts to make it work correctly.

Bruce

Thank you for that Bruce...now I can tell you with 100% certainty that my choke wire has 12 volts going to it, and I can also tell you that the choke flapper does not move on my truck... I did not know it was supposed to so i rotated the plate held by the screws until i felt the engine ran fine... Im almost 100% sure the engine was hot at the time. So i left it about halfway open. And thats where it stays unless i floor the truck, in which case the rush of air pushes it open. To me this was normal operation. Obviously to an experienced carburetor informed person as yourself, im an idiot lmao. Now, my truck does have an issue where the idle will be kinda high on it, but if i blip the throttle it goes down. Im unsure of this has anything to do. What can I do to fix that and/or get the choke to work properly?? Some more info for you, my choke light does NOT come on if im ignition on/engine off. It used to! Back before i had the carburetor rebuilt and the previous owner had a manual choke on it(the choke wire was just laying there). I never paid much attention to it cuz to me the truck was running alright, except for that idle issue...

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[deve05]

Rock on @75gmck25

Thanks man, for bringing him on, just from that one post of his i can tell he's a carb guru lmao, i know cuz everything he said I didn't know about and what i did think i knew about i did wrong lmao

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[Honky Kong jr]

Thanks man, for bringing him on, just from that one post of his i can tell he's a carb guru lmao, i know cuz everything he said I didn't know about and what i did think i knew about i did wrong lmao

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Lol I accually tagged some one else Bruce was just passing by and laid a bunch of good info on you.

 

[1987 GMC Jimmy]

Well, looks like my work here is done... Jk, that's your fast idle setting when it's idling higher than normal cold. Blipping the throttle brings you down. That's what it's supposed to do. Now, if it's ridiculously high, it needs to be adjusted, but a good fast idle is relatively high. I don't know what the factory spec on it is, but I'm thinking like 1100-1200 RPM. What Bruce said really hit the nail on the head, and I don't think I could add anything to it. I did notice you said you don't have a thermostat in it. I don't think that's ever a good idea outside of an emergency situation. If a thermostat makes it overheat, you have a cooling problem somewhere that should be addressed. Yours would do well with a 180* stat, and if it were me, I'd make figuring that out my next project.

 

[deve05]

Well, looks like my work here is done... Jk, that's your fast idle setting when it's idling higher than normal cold. Blipping the throttle brings you down. That's what it's supposed to do. Now, if it's ridiculously high, it needs to be adjusted, but a good fast idle is relatively high. I don't know what the factory spec on it is, but I'm thinking like 1100-1200 RPM. What Bruce said really hit the nail on the head, and I don't think I could add anything to it. I did notice you said you don't have a thermostat in it. I don't think that's ever a good idea outside of an emergency situation. If a thermostat makes it overheat, you have a cooling problem somewhere that should be addressed. Yours would do well with a 180* stat, and if it were me, I'd make figuring that out my next project.

Thanks for the info man. So then what I'm gonna do next is put a thermostat in it and see if it'll go out of fast idle on its own once it gets up to temp. I'm also gonna try to figure out if I can get the choke to work properly. I'll continue updating this thread as I go along so hopefully it'll help the next guy along! Thanks to all of the great guys that replied and gave info! I really appreciate it!

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[deve05]

Sooo... Uhhmmm, just an update... So I haven't had any time to tear into the truck cuz of work, but today on my way home the misfire started going away while accelerating... From the time it started going away to the time it completely stopped was maybe 20-30 seconds... I have not touched the truck... So now I'm 100% sure its a carburetor issue. Either that or the Chevy gods have blessed my truck and cured it of the terrible misfire lmao

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[Frankenchevy]

just to add to the good info you already got...make sure the ground side of the choke is grounded to the frame or block, not the manifold. the manifold is isolated by its gasket. if its way outta whack, set the choke with gas pedal by pushing it all the way down when the engine is cold and off. remove your air cleaner. loosen the screws on electric choke. manipulated the round black housing till you see the choke plate open and close. since the engine is completely cold, slowly rotate the black housing from slightly open until it just starts to fully close and rest shut on the carburetors body. start somewhere around there.

now...if the choke is properly grounded and you have set it with the gas pedal, fire it up and let it idle. it should idle high.

once it is warm, which will take forever without a thermostat, blipping the throttle should relax it into low idle. notice that the plate will be completely open now. if it is not, something is wrong with adjustment or electric choke mech. when choke is adjusted, lock it back in with three phillips screws. after you adjust the choke and the car is completely warm you need to adjust idle mixture and speed again. make sure you check your adjustments with the air filter in place.

keep in mind, this choke is set with the throttle. you should fully depress the throttle pedal before you attempt to start the engine. some people new to these carbs, especially when coming from fuel injection, overlook that simple step.

 

[Frankenchevy]

you need a thermostat. your engine would operate better if allowed to reach 180-195 degrees. a thermostat is what lets it get there faster. in some engines, the absence of a thermostat can cause cavitation at the water pump. i'm a newb with sbc so i'm not positive on that last point. either way its a few bucks and a few minutes. bleed the cooling system afterwards.