The comments are helpful on trouble shooting this situation, thanks.
Unfortunately,
they are mainly helpful in determining that I have done what is needed so
far with no success. The first thing I did was balance the carbs as I have done
in the past using a twin engine manifold pressure gauge connected to each
side the engine. That has in the past been very effective in getting the engine
balanced and smooth. I founf a very slight imbalance, but that is now gone.
The problem is that although the imbalance is gone, the engine is running
exactly
the same as it was before. If it were carb balance, I would not think it would
have a narrow range of rough running. This thing is "missing", not just
vibrating.
I have worked with engines for many more years than I would like to
admit and this engine is misfiring on both ignitions in a way it would due to
mixture. I am now checking the fuel pressure readings and will do a flight to
see what those values are doing with respect to what they should be doing. I
need
also to check the function of the float valve to insure there is no leak there.
The bottom line is that the engine was running smoothly and now is missing
in a fairly narrow range of power setting.
On behalf of the Rotax, I am now up to 232 hours of operation. You will notice
that I am going to fly the airplane to take readings, which illustrates my
confidence
in the engine. This is a situation that I do not feel is going to make
the engine quit, but is a matter of perfecting the running characteristics. If
this were your lawn mower, you would not even notice it. My philosophy is to
catch the problems when they gernimate, rather than waiting for them to progress
to the stage of being a true problem. I just got through with a 3,000 nmi
flight to Oshkosh and the airplane didn't skip a beat the entire flight. I also
operate a twin comanche with two bullet proof Lycoming engines in it. Although
they are great engines, they require constant attention to insure safe and
proper operation. At this point, I have no ill feelings toward Rotax. I do wish
they had fuel injection and I was not too impressed with the rubber carb
flanges,
but I think I have a handle on the flanges with the airbox supports fabricated
and now with about 8 hours of running. The efficiency and quiet operation
of this engine is quite impressive. Keep in mind it is a turbo charged engine
and those by nature are more complicated requiring more maintenance and
attention.
you don't get something for nothing! The pay-off is being able to climb
the mini U2 at 95 knots indicated at climb power - 900 FPM all the way up to
17,500 feet! That makes this effort to resolve the occasional problems worth
it.
When I figure this out, I will post the result here and on my little web site.
Dave
A227
Mini U2
232 hours TT
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