Rotax 912 ULS - Carb and Idle issues....

[MarkGoolie]

Last month I had the carbs on my Evektor SportStar services by a Rotax service center. I have had issues with the idle setting since it was worked on and it has been back to the same mechanic 4 times now with no resolution.

Here is what happens. He syncs the carbs, sets the idle. We run the plane for a bit and the idle is off. The idle speed usually drops enough to kill the engine when you pull throttle to the idle position. Anyone ever seen this before or have any ideas of what may be going on?

Thanks,
Mark

[roger lee]

Hi Mark,

Things to check and not necessarily in this order. A small foreign object in a carb ( not too likely), float bowl level off (more likely), enricher circuit (choke valve setup not replaced correctly) (more likely). Make sure vents coming off carbs are not kinked and are both in the same position. Carb slide not straight (not too likely). Unfortunately these carbs may need to be removed and checked inside. If they are running good at higher rpm and just die at idle then I would look at the float level, needle and enricher circuit first. Check the mixture control screw for 1.5 turns out on the bottom of the carb. They are either being starved for fuel or flooded, so think along those lines. It may just be one carb causing the problem. It's hard to tell noting actually being there.

[MarkGoolie]

Roger,

Thank for the internet diagnosis! I'll run this by the mechanic today and see if he can find anything along those lines.

The engine seems to run ok at the higher rpm. It may be a little rougher than it was before the carbs were rebuilt. The biggest issue is that the idle speed is never consistent and the engine shutting down when the throttle is at the idle position.

Thanks,
Mark

[Helen]

He may also be setting the idle setting while it is at a proper temperature and you may be running it cold. Rotax engines idle at different speeds when they are at different temperatures. We always set ours higher than recommended so the engine is sure to run smooth even if cooled on a cold morning in a long traffic pattern.

Helen