66cc motor WOT problem

Discussion in 'Introduce Yourself' started by Bgnlb, May 25, 2014.

  1. Bgnlb

    Bgnlb Member

    My 2nd bike started dying at full throttle,I removed filter in tank and swapped out carbs. I had a expansion pipe on it. I put the stock pipe back on,no more cutting out at hi rpm. Has anyone had same problem,is it a back pressure problem?

  2. Fabian

    Fabian Well-Known Member

    More than likely it's a carburation issue/air leaks issue.

    The only effective method that gives absolutely reliable carburation is a Walbro style (diaphragm) carburettor, as used on chainsaws.
    They don't leak (fuel or air) and have external jetting adjustment to zone in on the perfect air/fuel ratio; keeping the jetting setting locked in place once set.
  3. Bgnlb

    Bgnlb Member

    I think it's a back pressure problem. When I had expansion pipe on it would cut out at hi rpm. I put the stock pipe on and no problem at hi rpm. In the 70's 2stroke road race motorcycles had 8-16 inch stingers
  4. Fabian

    Fabian Well-Known Member

    It's sounds like a jetting issue. Once the air/fuel ratio is optimised for your setup the engine will run correctly.
  5. butre

    butre Well-Known Member

    there's not really such a thing as a back pressure problem. There's overly restrictive and there's poor scavenging, neither of which have anything to do with pressure.
  6. Bgnlb

    Bgnlb Member

    You're rite,when I had expansion pipe on,it would run good when I fiddled with petcock