Rpm RISE with carb heat
in 912 / 914 Technical Questions
6 years ago
Hello all,
I have been experiencing a strange thing on my 912ul powered Kitfox.
When pulling carb heat with the engine running at any speed above 3000 rpm the rpm increases with about 150 rpm. Very opposite of what could be expected of course.
Running without the air filter does not change this behaviour, so an air blockage is not likely in my opinion.
Main jets, needles and other carburetor parts are looking fine
The spark plugs indicate a normal mixture.
The carburetors are set up according to the manual and do require only minimal adjustment to balance, which in my opinion indicates that there is no problem with a single carb.
The engine seems to run slightly rough when accelerating through about 3000 rpm with cold air. With carb heat on acceleration is absolutely smooth.
I do have problems getting the engine to proper operating temperature, always operating just above recommended minimum cht and oil temp.
Could this be the cause of this effect?
I have had this issue for a couple of years now, and to me it does not seem to be a threat to flight safety. It does irritate me however that I do not know the cause of this effect.
On top of that it makes me wonder if the engine is lacking power in general, since my Kitfox seems to be flying on the slow side....
I would really appreciate any input from anyone with more knowledge then me!
Jan
I have been experiencing a strange thing on my 912ul powered Kitfox.
When pulling carb heat with the engine running at any speed above 3000 rpm the rpm increases with about 150 rpm. Very opposite of what could be expected of course.
Running without the air filter does not change this behaviour, so an air blockage is not likely in my opinion.
Main jets, needles and other carburetor parts are looking fine
The spark plugs indicate a normal mixture.
The carburetors are set up according to the manual and do require only minimal adjustment to balance, which in my opinion indicates that there is no problem with a single carb.
The engine seems to run slightly rough when accelerating through about 3000 rpm with cold air. With carb heat on acceleration is absolutely smooth.
I do have problems getting the engine to proper operating temperature, always operating just above recommended minimum cht and oil temp.
Could this be the cause of this effect?
I have had this issue for a couple of years now, and to me it does not seem to be a threat to flight safety. It does irritate me however that I do not know the cause of this effect.
On top of that it makes me wonder if the engine is lacking power in general, since my Kitfox seems to be flying on the slow side....
I would really appreciate any input from anyone with more knowledge then me!
Jan
