Idle Speed Adjustment

[65 Mustang]

I'm running an autolite 1100 on a 200 ci engine. I improved my cylinder compression by replacing the head gasket. However, the cylinders still only average about 115-120 psi. The shop manual recommends hot idle speed of 500 to 525 rpm. I assume this means for optimum cylinder performance (155 to 195 psi). When I bring my idle speed to 500 -525 the car frequently stalls when I come to a stop. I find that she runs best with an idle speed close to 700 rpm. That is, no stalling issues. In park, the engine revs to about 1000 rpm. The only problem is that the car jolts forward a bit when I put it in gear. I can live with that, but could any problems develop as a result of keeping the idle speed high?

Also, does anyone have any suggestions for adjusting the hot idle speed as well as the air/fuel mixture? I let the car warm up. I then turn on the headlights, radio, and turn signal. The car is automatic so I have a friend put it in drive and keep his foot on the break. I then turn the the hot idle screw to achieve the desired rpms. I then adjust the air/fuel mixture until it feels a little smoother.

 

[ludwig]

Is it stick or auto? Stick wants a low idle speed, like 500/550 rpm. Auto should be about 700/750 rpm and set to that while in Drive. Check your idle fuel mix by screwing the mix adjusting screw in until the engine starts stumbling. Then back it out until it smooths out, then about a quarter turn more. If you have a vacuum gauge, adjust it to the max vacuum. This should be higher than 18*. You can time it with the vac gauge too. When at idle, advance it until the vacuum is highest. Then set the idle back down to 700/750 rpm.

 

[bubba22349]

The only problem is that the car jolts forward a bit when I put it in gear. I can live with that, but could any problems develop as a result of keeping the idle speed high?

Yes it's not good for trans and u joints?

As long as all the cylinders are close to same compression you should be able to tune it to run smoothly enough. If it still stalls you might look at accelerator pump function.

 

[65 Mustang]

Thanks for the info. What would be the best way to see if the accelerator pump is working correctly?

 

[ludwig]

Look down the carb throat and push the throttle lever down. You should see a spray of fuel into the throat. If not, or if the fuel is not atomized, the pump is not working.

 

[JackFish]

I'm running an autolite 1100 on a 200 ci engine. I improved my cylinder compression by replacing the head gasket. However, the cylinders still only average about 115-120 psi..

If the gasket you swapped out was a thin metal one, and the one you replaced it with was a modern composite, then you have lower your compression ratio due to the increased thickness of the new gasket.
Most of us have the head shaved to compensate, and bump up the CR.