Lose power with quick throttle advance

[urielusa]

Hi I'm new. I have a 1946 BC12-D with recent engine overhaul. I duct taped the cowl for winter flying and then one day the temp got up to 32 and the oil temp went up to red line. I changed the oil and took some of the tape off. The next time I went to fly the engine started as usual but on run up with quick throttle advancement the engine wanted to die, Talked to mechanic thought maybe water or such. I put in dry gas seemed to make it better but same thing still happened but not as bad. The ambient air temp about 7 deg F for all this. Today with temp like 20 F engine started easy and ran well, rapid throttle movement caused stumbling but if I add power more slowly it runs like a charm. Also if I pull carb heat and rapid advance seems to be better. SO it seems to me that engine is running a bit lean and maybe no other big problem. Would running hot for a while cause this or is it coincidence or something worse? Thanks for your consideration.

[AndyDuke]

Re: Lose power with quick throttle advance

Sounds like you are causing a lean cut by being too agressive with the throttle. On some carbs like the strombergs used on 65 hp engines, there is no accelerator pump which would normally push more fuel through with quick advances of the throttle. When there is no accelerator pump, you open the throttle quickly which increases the amount of air but no immediate increase in fuel, so the mixture is momentarily leaned and the engine runs rough.

This is why, you don't get a problem with smooth throttle changes. Just be gentle, these old airplanes like a gentle touch.

[urielusa]

Re: Lose power with quick throttle advance

Thanks for the quick reply. That's what I was hoping is the answer it just bothers me that I hadn't noticed this before.

[robbie]

Re: Lose power with quick throttle advance

warmer the weather less you will see this problem.

[urielusa]

Re: Lose power with quick throttle advance

Thanks. So is this consistant with the age of the engine and carb?

[Ragwing nut]

Re: Lose power with quick throttle advance

yes it is. I have never understood why Taylorcraft never placarded this. Luscombe did as well as several others for throttle advance no faster than 3 seconds if I remember right.

Mike

[Karl Rigdon]

Re: Lose power with quick throttle advance

In colder temps I always leave the carb heat on full untill I have the throttle fully open. The heated air will enrichen the mixture. Also when taxing in tall grass that has dew in the early morning I have picked up carb ice on the ground. That is with temps from 40 to 75 deg. or more. With carb heat be aware you do not have filtered air going into the engine.

Karl

[AlvinMcIver]

Re: Lose power with quick throttle advance

Check out the Continental Service Bulletin attached.
Alan

[urielusa]

Re: Lose power with quick throttle advance

Thanks a lot for taking the time to post that service bulletin. Have you made the mod to your t craft and does it help?

[AlvinMcIver]

Re: Lose power with quick throttle advance

Yes, and Yes. Prior to installing it during the Winter months, I had about six instances in which the engine quit after landing and rollout even with gentle input of throttle. Also, it stumbled a number of times when clearing while in the pattern and quit once on final but restarted when throttle moved to idle. It was then that the article in TOC Newsletter came out and I contacted Cont for a copy of the SB directly from them. Since then, I have had no problems, but I am vigilant and ready with the primer if need be.
Alan