Engine max went from 34mph to 25mph? wth?

Discussion in 'Motorized Bicycle General Discussion' started by StrontiumEthics, Oct 9, 2009.

  1. StrontiumEthics

    StrontiumEthics New Member

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    I have a jackshaft kit, tuned pipe, and a dax 70cc engine. However today my engine started to act weird. Before it could hit 33-mph fairly easily. Now its struggling to hit 26-mph. What do you think the problem is? Chains adjusted right, bearings are good, just did a tuneup yesterday, and it was ok.
     
  2. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    What did you do to it yesterday?
     
  3. thatsdax

    thatsdax Member

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    Have you checked for fresh air leaks? If so.. How did you check? And..Did you find any? If you did find some fresh air leaks.... Where were the fresh air leaks? Let us know. Thanks.
     
  4. StrontiumEthics

    StrontiumEthics New Member

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    so air leaks can cause this im going to grease up these area's. But is there anything else?
     
  5. StrontiumEthics

    StrontiumEthics New Member

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    OK just sealed up the carb, and its still the same problem.
     
  6. StrontiumEthics

    StrontiumEthics New Member

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    Another peice of information is that, before (like 4 days ago) my bike can go up until gear 5 until engine can't use the gears. Now it struggles in gear 4 to even go faster. The torque was decreased.
     
  7. omegaunderground

    omegaunderground New Member

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    had the same problem with mine... my brother riding my bike could do 45 mph (he weights about 80 lbs less than me) but he could only do 28-30mph after my engine started acting up.... I replaced the gasket not the head gasket but the one on the other end of the head that has fuel tunnels on it. Got some power back but the engine still acts funny, I believe I have a fresh air leak.
     
  8. StrontiumEthics

    StrontiumEthics New Member

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    How do I check if I have a fresh air leak? Maybe im doing it wrong?
     
  9. mechanickid

    mechanickid New Member

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    i found out you need to check the head nuts too for air leaks, because they're not always sealed off, if you have too large of washers under the head nuts then air can go through there and cause minor problems. i solved this problem by drilling the perfect size hole in four pennies. (which are soft enough to seal well) i also re torqued my head nuts slightly after the first 4 warm ups because if there isn't enough pressure the gaskets will burn out and the threads are too week to get it tight enough the first time.
     
  10. Junster

    Junster New Member

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    Is the motor getting hotter than normal? I just had one of the pins in the piston ring groove that keep the rings from rotating come loose. It gouged a big groove in the side of my cylinder. I kept loosing power, the motor got slower and slower. Also harder to start. You can pull the head off and inspect the inside of the cylinder for this. I hope that's not it. I have almost $50 in parts on order to fix mine. To check for leaks turn up the idle then spray some wd-40 at the carb mount, intake mount, around the cylinder base. Listen for the motor to slow if you hit a leak. It will seal the leak for a few moments causing the idle rpm to drop.

    BTW; If your having compression loss thru the head bolts you need a new headgasket. You also probably need to use some wet/dry 220 grit sandpaper on a piece of glass and lap the bottom of your head till it's dead flat. The only way you can get anything into the holes for the headbolts is if the top or the bottom cylinder gasket is leaking.
     
    #10 Junster, Oct 10, 2009
    Last edited: Oct 10, 2009

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