912 UL wont rev past 4k
in General Tech Discussion
9 years ago
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by Roger Lee » 9 years ago
Did you set the float level? If it is not correct the fuel level in the carb may be too low. Make sure the needle valve is in correctly. The pistons in the carb should slide smoothly. If not take them out and clean them. If they have hardened debris on them use a scotchbrite pad and some carb cleaner and clean them. Have you synced them yet? This will tell you which is the offending carb and may help your diagnoses. Use gauges not an electronic sync tool. You can't diagnose with an electronic one like you can with gauges.
Overhauling carbs is easier with some experience because you know what to look for and where the pitfalls are.
Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell
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by Kevin Machniak » 9 years ago
Maybe a restriction in the fuel system supply. you can have pressure and not enough flow or volume.
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by Scott Buck » 9 years ago
I had set the float level as I replaced the floats with new ones to comply with the SB. Everything was normal and clean. Also Sync was right on.The only thing slightly abnormal was the slides, they would stick one out of 10 times- so pretty sure they are the culprit. I got tired of messing with these carbs and bought new ones. Plane runs smoother through all rpm ranges, and no issues so far, but I only have about a half hour flight time. Any long term issues running the needle clip in the second position vs. the third position? My new carbs are set in the second position. Thanks again for all the responses-
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by Roger Lee » 9 years ago
Hi Scott,
Usually when I overhaul the carbs I take some scotchbrite with carb cleaner and go over the slides and make sure they are clean and smooth so there is no old sticky residue on them.
The second notch might not be an issue, but I wouldn't do it unless you fly out of a fairly high elevation airport and tend to fly at higher altitudes. Changes in seasons from summer to a cold dry winter will affect this too. Cold dry air will make it run even leaner.
So if you end up in the perfect storm so to speak you could end up too lean. The whole idea is to not just get performance out of an engine, but to protect it and make sure it has a long uneventful life.
Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell
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