Rough idle

[70mustanguy]

I have a rough idle in my project car. I have started it up and everything seems steady besides the rough idle. I did a vacum check and got a good steady 20 inch. I think can be the timing ( have been playing around with it but am not getting anything to stop the rough idle), bad spark plug, or bad cylinder( hope not). I don't have the best knowledge of mechanics since I am only a high school student. But I have played around with it and am not sure whats with the idle. Any sugestions would be helpfull thanks.

 

[gregski]

I love rough idle threads, get ready for a 1,000 opinions, LOL, all I am going to say is check the simple stuff before you tear into that engine.

Whacha mess with last, tell us more?
Where is your timing set at?
Did ya tinker with the carbie?
Old spark plugs or new?
Old spark plug wires or new?

RUNNING ON OLD GASOLINE PERHAPS YOU ARE?

 

[skywalker]

I love rough idle threads, get ready for a 1,000 opinions, LOL, all I am going to say is check the simple stuff before you tear into that engine.

I second that.

Other questions: do you have an electric choke? Do you know what kind of cam you are running? Is your idle fast enough? What kind of carb are you running? While your vacuum gauge may say 20 inches, I know the Holley procedure is to start out at a standard setting, likely too rich and too fast, adjust the mixture to achieve MAXIMUM vacuum and then adjust the idle speed. If your idle mixture is off (or asymmetric) it can cause a rough idle, a fast idle and dieseling.

 

[67rcks]

I know the Holley procedure is to ... adjust the mixture to achieve MAXIMUM vacuum and then adjust the idle speed.

IMO it is not as simple as that. You can adjust idle speed so that .040" max idle slot is revealed. If idle is still rough you likely have some dirt idle/transition passages (assuming correct valve+ignition timing, no vacuum leaks, functioning power valve, etc.) Idle has to work on all secondaries too! It is one of holley's imperfections that you must tune idle air through main system, and there's no separate idle air tuning screw as in other carbs.

 

[gregski]

Does he even have a Holley? LOL

 

[skywalker]

Does he even have a Holley? LOL

Hence why I asked what kind of carb

 

[skywalker]

IMO it is not as simple as that. You can adjust idle speed so that .040" max idle slot is revealed. If idle is still rough you likely have some dirt idle/transition passages (assuming correct valve+ignition timing, no vacuum leaks, functioning power valve, etc.) Idle has to work on all secondaries too! It is one of holley's imperfections that you must tune idle air through main system, and there's no separate idle air tuning screw as in other carbs.

In so far as there being another problem, you are right. In so far as a rough idle due to a poor tune, it is as simple as that though. You need a small flathead, a vac gauge and a tachometer and that is all to tune your idle. The tachometer part can be bypassed with decent ears.

 

[globaltefl]

Has anyone tried the PROZONE IDLE CONTROL valve? Are they any good?

 

[skywalker]

Has anyone tried the PROZONE IDLE CONTROL valve? Are they any good?

The wha?