J

JohnF

Well Known Member
After doing a mechanical synchronization, I used a CarbMate electronic unit to fine tune things. That CarbMate has settings from 2mm Hg down to 0.5mmHg. You keep fine adjusting and increasing the sensitivity until you get down to 0.5mmHg and equal balance.

I have (according to the instrument) exact balance at 1,800 RPM, but as I increase RPM there is an area in the 3,500 RPM or so range where there is some relatively minor inbalance. At 5000 the balance is again, per the unit, in perfect balance. That's about as good as I could get it.

Any comments?
 
Good to go John!

Most of the imbalance vibration is noticed at the lower end of the RPM range. Sound like you nailed it. As the plane breaks in the throttle cables with stretch and "wear in" a little and at annual you'll need to check it again.
 
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I don't know how relevant this is to the Rotax, but on BMW twin cylinder motorcycles we set the sync at two points: at idle with the carbs/throttle bodies on the mechanical stops, and just off idle when they are hanging on the cables. The off idle sync vary slightly through out the rpm range because both intake tracks are not a perfect mirror of each other, and one side flowes better than the other at different rpm's. While the manual tells us to just set the off idle sync at just a little off idle, around 1300 rpm (idles around 1100) those of us who are picky will set it at the cruise rpm we use on the freeway most of the time for the smoothest ride. Let the slight variations be in RPM ranges that we just pass through briefly while accelerating and be in perfect balance at the RPM we drone along in for hours.
 
Sync

Yes, Mike, that's what I thought...the slight variation around mid 3,000 rpm range is a 'pass through' rpm, the idle and the 5000 or so are the two that I thought were the most important..also I just noticed I said I had down to 0.5mm, I should have said 0.5cm.

JohnF
 
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