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Hello,

I changed the circlips on the main carb needle per the SB as part of my annual. Everything seemed fine. The engine started and ran smoothly. I let it warm up and ran through mag checks, fuel pump checks, responsiveness. It seems to run perfect up until a MAP of 28 and then shakes and RPM drops rapidly. Comes back smooth if throttle is reduced. I tried this multiple times and then went back through the carbs to make sure the diaphragms were seated correctly. Same problem, but decided to let it run at a MAP of about 27. After running for 5-7 minutes I was able to accelerate all the way to full turbo at a MAP of 39.8. I let the whole system cool down and inspected the bowl floats. Floats are good and don't sink, bowls were clean. I have now run it for over an hour with many starts, stops and mixed throttle settings. Seems to run great and smooth.... 

I did notice a little circular scaring on one of my needles. I plan to order new carb needles and replace them.

The only thing I can think of is that some debris entered the carb and was obstructing the main jet. Does this sound reasonable? I hate to not know what fixed a problem.

Thanks for any suggestions! 

  • Re: Problem after needle circlip change

    by » one month ago


    I did not experience any rough running issues with my 912 UL after completing the SB but I did find the same circular scarring you mentioned. It was contained in the three faint grooves that are scored into the jet needle below the circIip. I polished it away with 2000 grit sandpaper. Engine ran fine so not sure why yours is misbehaving 


    Thank you said by: Keith Butler

  • Re: Problem after needle circlip change

    by » one month ago


    I have been thinking this through and my latest theory is that a flake of the Torque Seal on the connection to the fuel pressure regulator may have fallen into the fuel tube when dissembling it. I will be sure from now on to remove all Torque Seal type material before removing any connection of this nature.

    Still open to any other comments.

    Thanks!

     


  • Re: Problem after needle circlip change

    by » one month ago


    Hi Keith,

    Just a thought..

    I found the left carb circlip in the #2 position. Later when i completed the right carb I found the circlip in the #3 position. That surprised me and I wondered if I had messed up on the left carb. I found one post here that said the engine may have come that way so I didn’t make any changes and all was welll. Just wondering how yours was set up?


  • Re: Problem after needle circlip change

    by » one month ago


    Mine was set up in number 2 and 3 also. Surprised me at first, but replaced them in the 2 and 3 positions respectively. I then did some research and saw your post. It makes sense because of less resistance to air flow at the turbo entrance.


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