Engine Surging

[mongo]

I have a 912 ul in my model 5 kitfox. The other day during a runup at 4000 rpm the engine starting surging. I have narrowed it down to the left carb.. Took it apart and everything looks ok. Anyone had this problem before ?

[Russell320]

Did you check the carburetor flange socket for cracks or if it's seated correctly?

Just a thought .......

[jdmcbean]

Would suggest checking the fuel pump...

Rotax also had a Service Bulletin regarding the fuel pumps.

http://www.rotax-owner.com/

[mongo]

Thank's for the information. I have sent both carbs off to Lockwook for rebuilds. I will post if my problem went away after the rebuild. I look at the rubber socket and it look llike new. Thank's again for the replys

[DBVZ]

Just to rule it out, you could replace the fuel filter pretty cheap. Open it up and see if it has anything in it that looks wrong. Should not effect just the left, but if it is gunked-up it would be a clue....

[mongo]

Got the rebuilt carbs back the other day, but still had the surging problem. After much trouble shooting found that the rubber boot was leaking at the carb mount. Took a few turns with the old screwdriver on the mount clamp and the problem was gone. Now back to flying !!!

[foxkit3]

Mondo, Glad you found your air leak causing a lean condition. I would recemend to buy a set of carb boots from http://jbmindustries.com/ way beter made than the rotax ones. Harder compound rubber makes for a better fit and less carb movement due to engine vibrations. I have a set, Very happy.