Anonymous asked in Cars & TransportationMaintenance & Repairs · 4 weeks ago

When I start my dirtbike engine it redlines to the max. What would be the cause of this? I attached a photo of my carburetor down below.?

I just built a go-kart with a 125cc Apollo Dirtbike engine on the front. I just finished wiring the CDI BOX/IGNITION  COIL etc, gave it a kick and she started up on the second kick (brand new engine). She redlined to the MAX. What would be the cause of it? I also noticed when I started it and when she was redlining, the choke lever was being spammed open and closed extremely fast. As you can see in the photo I tried my best to seal up any air leaks by putting grease over any creases where the carburetor gets attached to something, I even put tape over the fuel inlet hole. Any other reason the engine would be literally redlining to the max as soon as it starts?

Photo of the carb: 

Attachment image

3 Answers

  • 4 weeks ago

    Take the air filter off and work the throttle with the motor off. Make sure the slide moves freely and closes all the way. The needle in the bottom of the slide should be adjustable with circlips to raise or lower the needle in the main jet. If the slide moves freely and comes down and shuts with out hanging up try lowering the needle to give it less gas. A vacuum leak isn't going to make the motor run at full throttle. Is there a spring on the governor lever? No spring would allow the motor to high rev with no control.

    Source(s): Mitsubishi Master Tech
  • Scott
    Lv 7
    4 weeks ago

    Throttle stuck could be one cause. Vacuum leak could be another.

  • 4 weeks ago

    Because you installed the slide incorrectly and it is stuck wide open. The slide has a groove in it that lines up with a pin inside the carb. A vacuum leak will not be the cause.

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