carb heat question

[Tom G]

Since my airplane is back together I've noticed a considerable difference in the rpm drop on runup with the carb heat on. The mags had new points installed and the exhaust was replaced with the same stock system that was taken off. I used to get a really large drop maybe 200rpm and now I'm getting maybe 50-75. The heat box is set up correctly and the cable is moving it full travel. My mechanic says as long as I'm getting a drop its ok. Any thoughts?

[Dano"T"]

Re: carb heat question

Normal RPM drop from adding carb heat is 50 rpm's I've seldom had more than 100rpm.

[dedrekon]

Re: carb heat question

I agree........50 is normal. 200 would've bothered me unless I was flying behind a Rotax where that is the normal drop.

V

[Tom G]

Re: carb heat question

Thanks guys, that makes me feel better.

[Forrest Barber]

Re: carb heat question

that larger previous drop may have been due to restricted air OR a leak in the exhaust system allowing hot gases to enter the system. THAT is a sure sign of a leak, if you get a big drop over 50-75 check it out.

[Tom G]

Re: carb heat question

Thanks Forrest, you definitely hit on it. The exhaust system was replaced and a large hole was found on the inside of the pipe near one of the cylinders. It was replaced because of the condition of the tailpipe which had already been repaired once. When the system was removed that hole was found.

[Forrest Barber]

Re: carb heat question

I almost kicked the end out of the cradle the first time I learned that could happen