uneven idle leading to cut off

Those symptoms sound like carburator icing. What was the air temp at the time?

Do you have working manifold heat and warm-air intake?

Max

"When its at operational temps the idle rpms rise and lower slowly and then eventually the engine cuts off, especially at lights. Any ideas?"

Check that the pre-heat tube isn't clogged, as this can cause carb icing. You can test it by BRIEFLY touching the preheat tube once the engine is warmed up. It should be hot enough to burn you on both sides, if not you need to focus on repairing that problem first. Fixing it is rather straightforward, remove the intake manifold and then use an old clutch cable to clear it out. Chuck the threaded end of the cable into a drill and cut the cable so it is slightly longer than half the length of the intake. Use it as a roto-rooter type tool with the drill to clear out the carbon. Work it from both sides and use compressed air as needed to remove the chunks as you progress. If this is the problem you'll be amazed at how much better your bug runs when you are done with this job.

The other possibility is that the carburetor itself is in need of an overhaul, or you may have an air leak around the throttle shaft. The latter is fairly easy to test, get the car warmed up and while idling spray some carb cleaner around the ends of the throttle shaft. If the idle goes up you have an air leak. Fixing it requires the bushings in the carb body to be replaced.

Looks like 40 bucks will get you a properly repaired carb casting that you can overhaul and put back in service. Alternatively you could purchase a new carburetor. If you don't find evidence of an air leak around the throttle shaft you could just overhaul your existing carb. The overhaul kit usually runs about 10 bucks.

Chris

"When its at operational temps the idle rpms rise and lower slowly and then eventually the engine cuts off, especially at lights. Any ideas?"

Check that the pre-heat tube isn't clogged, as this can cause carb icing. You can test it by BRIEFLY touching the preheat tube once the engine is warmed up. It should be hot enough to burn you on both sides, if not you need to focus on repairing that problem first. Fixing it is rather straightforward, remove the intake manifold and then use an old clutch cable to clear it out. Chuck the threaded end of the cable into a drill and cut the cable so it is slightly longer than half the length of the intake. Use it as a roto-rooter type tool with the drill to clear out the carbon. Work it from both sides and use compressed air as needed to remove the chunks as you progress. If this is the problem you'll be amazed at how much better your bug runs when you are done with this job.

The other possibility is that the carburetor itself is in need of an overhaul, or you may have an air leak around the throttle shaft. The latter is fairly easy to test, get the car warmed up and while idling spray some carb cleaner around the ends of the throttle shaft. If the idle goes up you have an air leak. Fixing it requires the bushings in the carb body to be replaced.

Looks like 40 bucks will get you a properly repaired carb casting that you can overhaul and put back in service. Alternatively you could purchase a new carburetor. If you don't find evidence of an air leak around the throttle shaft you could just overhaul your existing carb. The overhaul kit usually runs about 10 bucks.

Chris

"When its at operational temps the idle rpms rise and lower slowly and then eventually the engine cuts off, especially at lights. Any ideas?"

Check that the pre-heat tube isn't clogged, as this can cause carb icing. You can test it by BRIEFLY touching the preheat tube once the engine is warmed up. It should be hot enough to burn you on both sides, if not you need to focus on repairing that problem first. Fixing it is rather straightforward, remove the intake manifold and then use an old clutch cable to clear it out. Chuck the threaded end of the cable into a drill and cut the cable so it is slightly longer than half the length of the intake. Use it as a roto-rooter type tool with the drill to clear out the carbon. Work it from both sides and use compressed air as needed to remove the chunks as you progress. If this is the problem you'll be amazed at how much better your bug runs when you are done with this job.

The other possibility is that the carburetor itself is in need of an overhaul, or you may have an air leak around the throttle shaft. The latter is fairly easy to test, get the car warmed up and while idling spray some carb cleaner around the ends of the throttle shaft. If the idle goes up you have an air leak. Fixing it requires the bushings in the carb body to be replaced.

Looks like 40 bucks will get you a properly repaired carb casting that you can overhaul and put back in service. Alternatively you could purchase a new carburetor. If you don't find evidence of an air leak around the throttle shaft you could just overhaul your existing carb. The overhaul kit usually runs about 10 bucks.

Chris

Are you familiar with the tuning procedures? Can we assume that the ignition system is in good tune and timed properly? Is the carb throttle plate stop, idle bypass screw, and idle mixture screw set up properly?

If so, it's probably carb icing as already pointed out. Just below the base of the carb, is it frosty? One easy way to verify that icing is causing the problem is to idle it in your driveway with it acting up. Direct a heat gun (or hair dryer) into the air intake and see if it goes away. Then you'll know where to direct your efforts.

RT

Air leak?

Jan

Thanks everyone! The weekend is coming up and I can do more diagnostic based on your suggestions.

I had not checked the heat risers or the base of the carb for hot/cold.

The engine is tuned to spec. The temperature was 27 degrees with the humidity around 15% when I first noticed this although its doing the same thing at higher temps and humidity. The engine at each instance was cutting out at the first light after coming off I-64 at 65mph. indicated.

David