912UL Carb idle mixture
in 912 / 914 Technical Questions
10 years ago
Hi all,
I recently became the owner of a 912UL on a GTE912 trike. The 2001 vintage 912 has 232 hours so it has spent a lot of time sitting.
The long story follows but the question is why does the idle mixture screw on the 2,4 side need to be closed on this engine for a smooth idle (1800 rpm)?
Thanks in advance for any responses or suggestions.
History -
To bring it back to a safe flying condition. I did the rubber replacement items, new fluids, new sparkplugs, carb rebuilds, etc.
Initially, the plugs from the 1,3 side came out with tan coloration. The 2,4 side were glossy black.
After all maintenance items were done, an engine runup was performed, compression checked good and the carbs balanced. The engine ran smoothly above idle but shook quite a bit at idle (1800 rpm).
After various checks, it was discovered that idle would smooth out if the 2,4 idle mixture screw was turned all the way in???
The bowl was removed, fuel level checked and the idle jet and idle mixture screw was checked - all ok. Eventually the idle jet and mixture screw was swapped to the other carb - no change. Also, the fitting and direction of the "choke" was checked - again, it was ok.
I hope to get to get to the bottom of this problem but I am stumped at the moment.
Thanks again,
Charles
I recently became the owner of a 912UL on a GTE912 trike. The 2001 vintage 912 has 232 hours so it has spent a lot of time sitting.
The long story follows but the question is why does the idle mixture screw on the 2,4 side need to be closed on this engine for a smooth idle (1800 rpm)?
Thanks in advance for any responses or suggestions.
History -
To bring it back to a safe flying condition. I did the rubber replacement items, new fluids, new sparkplugs, carb rebuilds, etc.
Initially, the plugs from the 1,3 side came out with tan coloration. The 2,4 side were glossy black.
After all maintenance items were done, an engine runup was performed, compression checked good and the carbs balanced. The engine ran smoothly above idle but shook quite a bit at idle (1800 rpm).
After various checks, it was discovered that idle would smooth out if the 2,4 idle mixture screw was turned all the way in???
The bowl was removed, fuel level checked and the idle jet and idle mixture screw was checked - all ok. Eventually the idle jet and mixture screw was swapped to the other carb - no change. Also, the fitting and direction of the "choke" was checked - again, it was ok.
I hope to get to get to the bottom of this problem but I am stumped at the moment.
Thanks again,
Charles
