78 Qjet stuck on fast idle?

[wazzabie]

This is a 1978 4bl qjet.  I pump the gas peddle once and from a cold start, the fast idle is at 1700 rpm.  I'm trying to get the carb to normal idle which is around 700 rpm.  How soon after starting a cold engine should the rpms go to 700 rpm? 

[Cliff Ruggles]

What is the carburetor part number?

What application?

[wazzabie]

Thank you for the reply. 

The model number is 17058213.  The qjet is the original carb to a 78 K5 Chevy Blazer with HD federal emissions.

[wazzabie]

Also after about 3min at high idle (1700 rpm) I tap the gas.  I notice that the high idle cam falls down but it still runs at 1700 rpm.  I have not placed the vehicle into drive.

[Cliff Ruggles]

The choke flap should be fully open after 3 minutes run time and the fast idle cam should fall ALL the way down.  At this point it should be at curb idle and adjusted on the drivers side of the carb. 

Might help to lubricate the choke parts on the passengers side of the carb to make sure something isn't sticking and not allowing it to return to curb idle.....

[wazzabie]

Hi Cliff,  I tried using some wd40 to lubricate the pivot point for the fast idle cam and still have the same condition.  The fast idle cam moves down when I tap the gas but not enough to engage curb idle.  I have to manually push down the fast idle cam the remainder of the way to engage the curb idle.  I'm thinking about adjusting the fast idle cam screw to loosen some tension.  Your thoughts?

[lightning boy]

Does this carb have a rear choke pull off?

[wazzabie]

Does this carb have a rear choke pull off?

No.  The carb just has a single primary choke pull off.  The choke pull off retracts when the engine starts.

[Cliff Ruggles]

The divorced choke on the intake should get hot enough after a few minutes of run time to overcome the spring inside the pull-off and allow the fast idle cam to drop to the lowest position and over to the curb idle screw.

Check the divorced choke to make sure it's heating up and pulling down hard on the choke.....

[wazzabie]

The divorced choke on the intake should get hot enough after a few minutes of run time to overcome the spring inside the pull-off and allow the fast idle cam to drop to the lowest position and over to the curb idle screw.

Check the divorced choke to make sure it's heating up and pulling down hard on the choke.....

Maybe I'm not waiting long enough for the engine to warm up.  I tap the gas after about 3min and it still remains at 1700rpm.  I have to manually push down on the fast idle cam to obtain curb idle.

[Kenth]

Is the crossover channel in intake open or did someone close it?

[wazzabie]

Is the crossover channel in intake open or did someone close it?

I don't understand what you are asking.  What is the crossover channel?

[Kenth]

Crossover channel marked yellow. It heats the manifold for a functional choke and helps convert liquid fuel into a combustible gas.

[wazzabie]

Crossover channel marked yellow. It heats the manifold for a functional choke and helps convert liquid fuel into a combustible gas.

There has be no change from stock with the manifold.

[Jeff K]

I've had a few that just didn't want to work right. I end up putting a cable on them and every single time I was so happy I did that. If you do use the cable, keep the fast idle cam operational.