HT problem... engine surges at full throttle

Discussion in 'General Questions' started by macarollo, Oct 1, 2008.

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  1. macarollo

    macarollo Guest

    I have a 70cc HT kit. When I am running full throttle (vibration is pretty bad) every now and then the engine will surge... like it isn't getting fuel for a second, then it picks back up.

    under 3/4 throttle everything is fine.

    When I give it full throttle on level ground I notice that the fuel line is vibrating like crazy and I see air bubbles forming at the top of the line AND at the bottom of the line... eventually the whole line is filled with air bubbles, then it surges... if I let off the air bubbles clear and I can run full throttle until the line fills with air bubbles.

    One thing that seemed strange to me is that I see some air bubbles come up from the carb under WOT. Is this normal? Is there a leak in the carb?

    I have tried to tighten the fuel line, petcock, carb-manifold bracket, but it still surges once it is filled with air bubbles. It didn't used to do this.

    Any ideas for me?

  2. arceeguy

    arceeguy Active Member

    Does it bog after the bike "tops out" in speed? Or does it bog the moment the throttle is open more than 3/4.

    Check for good fuel flow by disconnecting the carb, and opening the fuel valve. Fuel should drain out at a decent clip. If it barely dribbles, check the fuel filter screen.
  3. macarollo

    macarollo Guest

    I bought an inline filter and discarded the stock filter. That seemed to fix the problem. Although the stock filter did not appear to be clogged. I blew through it and it did not seem to be restricted.

    I like the look of the inline filter better too.
  4. macarollo

    macarollo Guest

    Actually it still surges a little bit, but not as bad. Once it hits top speed it slows down a fraction then speeds back up, like it doesn't get quite enough fuel.
  5. andrewdavis19

    andrewdavis19 Member

    My bike does this sometimes too. My fuel line has air in it almost all the time. I still haven't got around to removing the factory filter on the petcock yet. I do have an in-line though. Is the surging a fuel related issue?
  6. Mountainman

    Mountainman Active Member

    most of the time -- I would say that it is -- fuel related

    makes it hard to Ride That Thing Fast Mountainman
  7. brendonv

    brendonv Member

    well if there is heaps of air bubbles in ur fuel line that means it may be bogging out because then it sucks in too much air as it already sucks in air through the air filter than its getting a big dose through the fuel line itself so wouldnt slightly choking it work so it gets the same amount of air in the fuel to air mixture?
  8. lowey

    lowey New Member


    i no this has nothing to do with power surges iwas just woundring if u had any idears on how to run my engine up side down i have an ider to make a plate to tak the fuel to the other side cause the fuel holes on the wrong side so the the engines up side down not the carby. You probly think this is realy convousing. i do but yer
  9. brendonv

    brendonv Member

    its a two stroke so it should be able to run upside down. My whipper snipper can.
  10. mikaleno

    mikaleno Member

    My engine was surging too. Seems to run smoother on 91 octane.