Ho 302 Rebuild Question

[Zigman]

Hi guys,
I transplanted an early 90's HO 5.0 into my II. I bought the engine components rebuilt, so I basically assembled the motor. Everything on it is new or rebuilt. New Edelbrock 600 cfm carb and HEI style dizzy (one wire). The engine runs good, but the idle quality is crap. The RPM's fluctuate from 900 to 1,000 RPM at idle. It also wants to die at anything under 1,000 RPM. When hitting the gas or driving it seems run very strong. I assume the engine has the stock cam, but I am not certain. I have the timing set at 36 degrees at full advance at 3,000 RPM with the vacuum disconnected, and it is about 14 degrees at idle.

At first I thought I might have a leaky intake manifold gasket, so I replaced it and it runs exactly the same. I am now out of ideas. Do you think it is carb related, or something deeper? The heads were rebuilt, but I don't know the specifics of either them or the cam. I hate to just keep throwing money at different parts without figuring out what the issue is. Since everything is new or rebuilt and aftermarket, I don't have a baseline and the engine has never idled good since I assembled it. Any thought or ideas would be greatly appreciated!

 

[jozsefsz]

Assuming your carb idle mixture is tuned decently (and float level set properly) there isn't really much other than vacuum leaks that will cause a hunting idle on a carbureted car. Make sure your PCV system is set up properly too otherwise that can behave like a huge vacuum leak, that or the vacuum booster for the brakes. Don't know if your distributor has a vacuum advance unit, if so make sure it's getting ported vacuum (little / no vacuum at idle). A vacuum gauge can help determine if you have low vacuum or if the rebuild of the heads left something to be desired.

 

[Zigman]

Thanks for the response. I think I will pick up a vacuum gauge and take some readings and let you know what I find. I played with the ported/non-ported vacuum to the dizzy and it seemed to run better with full vacuum at idle, but still not good. I will report back what I find with the vacuum reading.