qjet idle issue?

[wazzabie]

On a 78 4bl qjet after cold startup when I press the accelerator should the engine decrease from fast idle? Fast idle is currently at 1700 rpm.

[geezer#99]

Yes it should, but if the choke is set too rich it won’t.

[wazzabie]

Originally Posted by geezer#99

Yes it should, but if the choke is set too rich it won’t.

How would I know if the choke is set too rich?


Do I have to wait for this heat riser spring to heat up before the engine goes to normal cub idle?

[geezer#99]

Yes, it needs to heat up the coil.
Rich or lean is determined by the length of the rod. It needs to be bent to adjust.
Is this new parts instal or existing set up?

[wazzabie]

Originally Posted by geezer#99

Yes, it needs to heat up the coil.
Rich or lean is determined by the length of the rod. It needs to be bent to adjust.
Is this new parts install or existing set up?

The rod is original as is the spring.

I installed a new vacuum diaphragm and gaskets. I also removed and cleaned the carb.

Maybe I didn't let the engine warm up enough. I started the engine and then immediately tried to bring it to cub idle.

I can see that the fast idle cam dropped. I turned off the engine and manually moved the linkages. I then started the engine again and now it runs at 700-800 rpm.

I'm going to cool down the engine and then restart the engine and see what happens.

[400/400]

There’s actually two fast idles on the cam.

On initial start it should rev to the fast idle speed on the label, then a tap of the throttle will allow the choke pull off to reduce the idle to intermediate. Then after the choke coil warms up, it’ll let it come down to base idle.

The intake mounted and hot air choke coils take longer to warm up and allow base idle. Converting to electric choke usually allows it to happen sooner.

[wazzabie]

There is only one screw for fast idle. How do I set the two fast idle speeds?

[geezer#99]

The cam has two steps on it.
Just set it on the primary step (high idle) and when you tap the throttle it drops to the lower fast idle step.
Usually 1200 rpm high drops to about 900 rpm.