Electric Choke Issues

[TravisUT]

Apologies if this is a duplicate post; I'm having some issues with my carb and was wondering if anyone could help?

I have a Quadrajet 4 barrel, mounted to a stock intake on an 84 C20 454. I recently replaced the hot-air choke with an electric choke, and since then, almost every time I start the truck, I get wet black spatter shooting from the exhaust pipe, along with some fuel-smelling smoke. Once the engine warms (choke opens very quickly), the smoke clears and the truck runs great. With the hot-air choke, this problem didn't happen. Also, I recently replaced the spark plugs (they were all fouled, very carbon coated). I don't know if the fouling was just since the electric choke was put on, or if it's been running rich for the last 3 years (since engine and carb rebuild). I've tried adjusting the air/fuel mixture screws, based on RPM, but that didn't seem to help much.

Should I go back to the hot-air choke, or what can be done? I'm not a mechanic, but am comfortable with working on the equipment.

 

[fast 99]

Sounds like choke thermostat is either too tight or choke pull-off is bad or misadjusted. Is fast idle adjusted?

Some Q jets have a secondary choke pull-off. if that's the case both pull-offs would need adjusted.

Choke plate should be closed when cold. Within a couple seconds the pull-off should crack it slightly open.

 

[TravisUT]

Sounds like choke thermostat is either too tight or choke pull-off is bad or misadjusted. Is fast idle adjusted?

Some Q jets have a secondary choke pull-off. if that's the case both pull-offs would need adjusted.

Choke plate should be closed when cold. Within a couple seconds the pull-off should crack it slightly open.

What do you mean by the choke may be "too tight"?

My Quad has a secondary pull of, and I think they're adjusted right, but they're probably not! I just ordered a hand vacuum pump so I can verify the pull-off setups.

The fast idle should be adjusted as well, but same story...is there a simple, step-by-step process for setting/verifying that?

 

[fast 99]

Too tight, too much wind up of the thermostat bi-metalic spring. Some of the stats are indexed. If yours isn't indexed back it off until the choke plate opens slightly, then go the other direction until plate just closes. Be sure to do this with the throttle open slightly or the fast idle cam may hold the linkage stationary.

There is a spec on fast idle speed, warm engine. Someone else may know it. Guessing..... set on the first step of fast idle cam around 1100 rpm. Screw is on RHS under choke facing forward.

Assuming the rest of the tune up is good, timing, advances, ect. Any adjustments after setting the carb will change overall operation.

If this engine has been running excessively rich oil will be diluted. Change it or as the gas burns off carb settings will change.

 

[TravisUT]

Great, thank you. What's the best order to make those adjustments? Should I do the fast idle, primary choke pull off, secondary choke pull off, and then choke adjustment, in that order? Or a different order? I'm worried that one adjustment will mess up the other...

 

[TravisUT]

Ok...I think it's all adjusted now. Got the choke and pull off's set, and it seems to be running good. Didn't spit any wet black spatter, so that's a step in the right direction. Once it was running, I hooked a vacuum gauge up to the big manifold port on the front-bottom of the carb, and adjusted the idle mixture screws to vacuum. Both are set about 3 turns out, and I'm getting 18 inches of vacuum. Is that good/ok?

I'm still getting a bit of smoke, but only on revving; idle and drive is ok with no smoke. I pulled a plug and it was all black. I just replaced those plugs a couple of weeks ago, but I suspect the out-of-tune was causing issues, yes? I don't want to replace them until we're confident the underlying cause is fixed...thoughts?

 

[Matt69olds]

With the engine completely cold (sitting overnight would be ideal) floor the throttle once. The choke plate should snap shut and the throttle go up on the fast idle cam. Loosen the screws for the choke heater, slowly rotate it until the choke plate closes, then go just a tiny bit further. Tighten the screws.

Next, put a hand vacuum pump on the choke pull off. The choke plate should open. If not, it’s defective and needs replaced. There is a tiny bleed hole inside, so the choke pull off will slowly release on its own.

There is a specified amount the choke is supposed to open. Use a 3/16 drill bit as a starting point, adjust the setscrew on the choke pull off. Keep in mind, airflow thru the choke tower is supposed to keep tension on the pull off.

Watch this:

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And this:

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