'83 Camaro Berlinetta 2.8l V6 stock carb. Recently installed new choke thermostat as the PO had removed it and installed a manual choke, which wasn't even hooked up properly.

General question about the fast idle function really... What is it meant to do? Is it meant to heat up the engine when it's cold?

And if so, why does my car not initiate fast idle until it's already warmed up? And even further, it never uses the maximum fast idle... (There are 3-4 fast idle settings on the carb to my understanding, the lowest being ~1000 rpm, the highest at ~2200 rpm) Why not?

 

Nobody?

):

 

Fast idle keeps the engine running when the intake tract is too cold to properly evaporate the liquid gasoline in the airstream.

 

So, because the gas is to cold to vaporize, the solution is to put more gas in? That doesn't seem right.

Furthermore, why would it turn on after the engine has warmed up?

 

That is precisely why you need to add more fuel when cold. When the inside of the intake is cold the fuel sticks to it thus not going all the way to the cylinder. So you need to richen the mixture (choke flap) and increase the speed of the air (fast idle) to get it to the cylinders.

If your car only fast idles when it warms up then it is not set properly. Most likely the choke thermostat is not set properly. Depending on the tension of thermostat it will set the stage of fast idle. The stronger the tension the harder it pulls the choke closed and engaging the higher stage of fast idle. As it warms up it releases its tension and thus stepping down the fast idle while opening the choke flap.

There should also be a fast idle screw as well but this only adjusts the overall speed of all the stages of fast idle. So if you lower the highest stage of fast idle by say 500 RPM then all the lower stages will be 500 RPM lower.

 

Remember on carbureted cars you MUST stab the gas once before you turn the key the first time on an overnight-cold start. That "unloads" the linkage and allows the choke to close as well as the fast idle cam to engage. One of the little differences between a carb'ed motor and an EFI one.

 

I can have visibly see the choke closed as far as it goes, start the car after hitting the gas once, see the choke closed fully still, and it will only idle at around 600rpm (at 20 degrees far in this instance)...

I'll have a look at it this weekend when I have more time, if I get time even. Finals are coming up and I have a lot of projects due.

 

Just because the flap is all the way closed does not mean the fast idle is fully engaged. After the flap is closed you can still turn the thermostat to increase its tension and further engage the higher fast idle.

 

Try this next time you start the car cold. Have the air cleaner off so you can see the carburetor. Press the accelerator pedal all the way to the floor once and let off before you attempt to start. Before you crank the engine, get out and verify that the fast idle cam is on the high step of the cam. If it is, then crank the engine without touching the accelerator pedal at all. Once it starts, observe the engine RPM. If it is anything less than the spec on the emissions decal, get out of the car and look at the choke blade. It should be slightly open. If not, the engine is loading up and cannot get enough air to fast idle at the speed it should. You can test this by using your finger to slightly press the choke blade open. If the engine RPM then picks up (as I suspect it will), your first problem is that the choke pull off is misadjusted or not functioning at all. This would explain why your engine picks up RPM's as it warms up. As the engine warms, the choke blade starts to open letting more air into the carburetor. It is likely that the fast idle cam is still on the high step or second step at this point of the warm up phase, thus giving you a higher idle. Try this experiment and post your results. Depending on what you find, we will go from there.

 

There's still something wrong with your choke linkage if fast idle cam step isn't engaged after punching the throttle and lifting your foot off the pedal before cranking, on a cold start the choke spring should rotate the fast idle cam to the highest step (on a 60*F or less day) and the engine should idle around 2000RPM until you hit the pedal, at which time the choke vacuum pulloff has opened the choke partially and slapping the pedal after startup will allow the fast idle cam to come off the highest step. Too much oil and/or grease on the pivot shaft of fast idle cam will cause it to stick and not move freely, I use ATF (or WD-40) on mine as motor oil or lithium grease makes them stick too much.

 

The fast idle cam is likely engaged from what I read. As the car warms up a bit (choke blade starts to open) the idle speed picks up. This is a classic symptom of a choke pull off that is not functioning properly. It may be something else, but from what I read, this is the first thing on my list.

 

Hold on a minute. After you fire the engine the choke is still FULLY closed? It shouldn't be. There should be a vacuum canister somewhere on the outside of the carb that should pop the choke plate slightly open as soon as there is manifold vacuum present (i.e. the engine is fired and running). It's there specifically to prevent flooding the motor immediately after startup and keep it from burbling and gaging from an insanely-rich mixture that would happen if the motor was to be running with the choke FULLY closed.

Those vacuum canisters that perform this function do go bad sometimes.

 

What you are describing is called the choke pull-off. See my previous posts about this.

 

Yes, I know. Sorry, I somehow missed that you already covered the same ground I did. Usually I read more carefully than that, but apparently not in this case.

 

We both agree that his problem is likely the choke pull off. Since the owner has not posted in a while, I guess we may never know.

 

I've found out what the problems are. Yes, problems.

1: Gunked up linkage. Cleaned it up and everything moves smoothly.

2: Bent linkage. Found that out after a thorough cleaning. (No, I didn't bend it while cleaning, as I only used spray cleaner and compressed air). This was the culprit for lack of high idle.

3: Old broken choke pulloff. Got a new one installed.

Now everything works much better.


Thank you for all the suggestions, info, and advice.