In the past there was a thread about a rough running Rotax 912 engine. The author had changed about everything: plugs, had the carbs reworked, etc..  In the end he found that the vent tube had been changed or re-routed and caused leaning when the aircraft accelerated - hence pressure affecting the delicate balance of bowl  vs  internal carb pressure reference. 

I have been researching this phenomenon to advise a Rotax powered gyrocopter owner - same problem: runs fine on the ground but looses power as the gyrocopter accelerates building airspeed.

Would the owner of the thread please contact me off site at (madriver42@ gmail.com) or if there is a way to go back to this thread how do I do it??

Thanks loads - I already am aware of the problems caused by the re-route of the vent line I just need some facts to back it up in a real world situation.

Still grinnin

Phil Smith

CH - 701

Buhl, ID

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That was john mazzoli that was having the problem. The rotax install manual addresses this. John is on here a lot is hangered at Arlington and very active.

Marzulli  sorry john

Thanks to all who responded - what I took away from all this is to be hyper critical on inspecting the carb to boot junction and also vent lines..

Wish I had the pictures to attach -but on closer inspection  our local mechanic - found that the carbs were not fully seated on the carburetor rubber boot. I still want to see what was done to the vent lines.
Xenon IV Sport Gyrocopter
Rotax 912 ULST  (add on turbo)
Now the story is getting out - A mechanic, not local - had rebuilt and reinstalled the carbs after a forced landing due to a "worn clip" in the carburetor - still not sure whether or not they have looked at the vent lines.  All I can do is make suggestions.
 The last frackus caused the engine to lose power during takeoff - I witnessed that one and the guy never got above thirty or so ft then turned into the wind  -  slight cross wind - and then downwind while hanging on a thread...you can imagine the results.  The gear - Zenith type - was splayed out about ten inches and the nose wheel strut was bent and broken from the impact.  Lucky he ran out of ideas and altitude over a dirt part of the airdrome.
Believe it or not this guy owns a machine shop and the structure is all repaired the carbs bolted on and they - the local mechanic and some representative of the gyrocopter - are going to fly it tomorrow.
All I can say is "film at 10 pm on your local news".
Needless to say I think I would get some more professional opinions...all I can do is suggest.

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