Carb sync, another thought provoking problem

[roger lee]

Hi All,

Another mind probing problem and I’ll give the answer in a day or two after a few tries at an answer.
You just pulled the engine for the Rotax 5 year rubber replacement maint. Everything is back on, oil purged and new plugs. It’s time for the carb sync. You do your mechanical sync and head out to run the engine for the pneumatic sync. You start up and everything looks good and the gauge needles at idle are only 1“ of vacuum off and the idle is 1750. You throttle up to 3500-3800 rpm to start the high rpm sync. The needles here are 4“ of vacuum off. So you adjust the bowden cables to sync the two carbs and you run out of adjustment. You shut down make a cable length adjustment on the throttle arm and restart. Now the gauge needles at idle are 7”-8” of vacuum off at idle. (Frack) You try and try to get them closer, but the left carb doesn’t seem to adjust. The engine is running rough and is now down to 1620 rpm. This particular plane has a Dynon D120 EMS with all the temps available to you. Oil temp, CHT and oil pressure are good and normal. The EGT temp span warning is flashing yellow which means your EGT’s have a span greater than 120F and that’s about where they are. One EGT is 1050F on #4 cyl while the other is 900F on #3 cyl. You just can’t seem to balance these carbs. “Frack”

NOW WHAT AND WHY?


By the way these thought provoking problems I give are real problems that had a particular solution. I post these in the hopes that some day if you have something similar you may remember and find a quick and painless solution.