2g/225/hei Prefers Running At Higher Idle...any Help

Got my Jeep back from the exhaust shop and decided to throw the timing light on just to adjust idle speed. It was way high. I brought it down to 950rpm hot. Went inside and came back out an hour later after it had cooled off a bit, fired it up with choke, put the choke in and it dies. Granted 950 is even still much higher than the prescribed idle speed. The fuel in the tank is old because the Jeep was down for so long as I slowly worked through the Saginaw swap. I do recall needing more idle speed previously with fresh gas. Would you guys think I should hook up the vacuum gauge and adjust the carb and then plug vacuum advance and check idle timing at 750rpm? Or would you think the carb should come off for a cleaning. With the choke out giving me just a small hint of extra fuel and rpm it runs fine.

 

The idle circuits in the carb may be fouled with bad gas varnish. I would start by draining all the old gas, add fresh gas and try a carburetor cleaner to see if it helps. Even if it doesn't fix the issue the old gas should be changed out anyways just to eliminate it as a potential part of the problem.

Check for a vacuum leak. A common area for a vacuum leak is at the carb base gasket at the back side as shown here




With the engine running screw in the idle mixture screws all the way in to see if you can kill the engine, if it
doesn't die then you are not operating on the idle circuit. There's a good chance you are not with the RPM's up at 950+

 

Do you mean the two idle mixture screws? Should I see if turning them in all the way shuts it off or not? If it doesn't kill the engine (I doubt it will since i have to run above 1000rpm to keep it alive) should I take the carb down to clean? I'll check air leaks on the back tomorrow too.

 

Yes, the two idle mixture screws. If you screw them in until they are seated lightly and it still runs then you are not operating on the idle circuit.

Be sure to check for a vacuum leak as your description is indicative of one. I had a similar situation with a vacuum leak at the carb base gasket giving the same symptoms as you describe. Spray carb cleaner at potential vacuum leak areas, the RPM,'s will change if you spray an area that has a vacuum leak. An unlit propane torch can also be used to do this but the engine fan may blow the propane vapors away.

 

Thank you - I like that you gave me a game plan for tomorrow. Hoping its just a base gasket but if I need to take the carb down and clean we can do that too.

 

Yes definitely check for air leaks if you can take the screws in and are not getting any change in run pattern. Might be a long shot but check the condition of the butterflies as well. Seen some with some rust on them that made tuning the 2g off idle pretty much impossible. Also check the tiny air idle slot in the bore of the carb and make sure it is open and free of debris as well

 

If carb/vacuum leak tracking doesn't fix it; It's an odd fire, check the plugs to see how they compare bank to bank. It's possible you're on the wrong firing sequence where one bank is firing correctly, but the timing is way off on the other. It will run that way, but it won't run great.