zorin

I have a 911SC with a '87 3.2 L engine on it equipped with triple throat Zenith carburetor. Engine seems to run OK , air intake rate is adjusted to be equal on all cylinders. Idle mix is adjusted and idle jet Valves are cleaned often.

I have noticed that cylinders 3 and 5 are always running about 40% cooler than the other ones in idle speed. (110 C vs 195 C). I know this because at some point the idle was rough and to find the problem cylinder I measured the exhaust pipe of each cylinder. Changing the idle mixture does not seem to affect it.

Any suggestion is appreciated.
Thank you.

Steve Weiner-Rennsport Systems

I'd suggest carefully looking at ALL of the ignition components to ensure everything is working properly: plugs, wires & connectors, and cap & rotor. Be certain that the plug connectors are seated (thats a biggie).

After that, I do a leakdown test to make certain the engine is in perfect health and adjust the valves (this affects AFR's).

Then, I check for any small vacuum leaks and go through the carbs very carefully sp I know each cylinder is getting the exact same quantity of fuel and air.

zorin

Thanks Steve.

I took out the spark plugs and checked them. They all had carbon deposits except for number 6 which I use a hotter plug NGK BPK5ES (rather than the recommended 6ES) . So I am guessing the engine was running rich. I cleaned the ones that were in good shape and replaced the other ones. I gap them to .040" since I am using CDI for ignition. I also adjusted the idle jets for a leaner.
The car idles much better. Tomorrow I will check all the cylinders after I take the car for a run to warm up the engine to operating temperature.

Thanks again.

scarceller

Removed Bad post: just noticed this has carbs.