Fellow Europaphiles:
I'm at 10.5 hrs on my XS Monowheel. (Just getting the hang of landing
it on pavement) As you can see from the signature block it has a
Rotax 914 and Airmaster C/S prop. On the last flight the engine
developed a surge and a miss at full throttle at about 500' on
takeoff. When I retarded the throttle and surge stopped and miss went
away. After immediate RTB, pulled the upper cowl and began an
inspection. 1st thing noticed was that it was not really obtaining
full throttle. Only about 37.5 in MP. Full throttle is 39 in MP and
37 - 38 in MP is in the unstable range for the turbo controller. That
explained the surging. Located the reason the throttle wasn't going
to max and fixed it. Also checked both fuel filters. Secondary was
fine. Main was had considerable crud so it was replaced. I can now
get full throttle. Re-synched the carbs. Runs nice and smooth.
Now here's what happened today on a full-power, chocks-in, tail tied
down, run-up test.
Engine starts immediately. I kept the idle at 2000 - 2100 RPM to warm
up.
Engine warmed up, all temps and pressures in the green. Prop
controller set Auto and T/O. Main and Boost pumps are both on,
Advance throttle. Everything is OK up to engine RPM 5790 & MP 36 in.
When the throttle is advanced beyond 37.5 in MP the engine quits.
Like fuel starved or ignition cuts out. It just quits.
Retard throttle back below 37.5 in MP and it re-starts and runs
smoothly.
Throttled back to 4000 RPM and did a "mag" check. Left-Off drop is
about 275 RPM, Right-Off drop is 305 - 310 RPM.
Throttle back to idle and shut off ignition, the engine stops and
after about 15 seconds there was a large backfire through the exhaust
(first time for that!).
Engine has only run on 100LL with appropriate amounts of Decalin TCP &
Marvel Mystery Oil to help with the lead situation. Oil is still nice
and clear.
Do any of you Rotax Gurus have a suggestion as to why the engine cuts
out when full throttle is applied? Any suggestion for things to check
and/or fix?
Thanks in advance for your help,
Bob Borger
Europa Kit #A221 N914XL, XS Mono, Intercooled 914, Airmaster C/S
http://www.europaowners.org/N914XL
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Corinth, TX 76208
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