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Mercarb Low RPM at Wide Open Throttle

Carburetor runs fine except at wide open throttle.
Assuming the engine compression is OK, the plugs are good and other ignition parts are good I suspect a lean condition. 

  • Test the fuel pump pressure – around 5 lbs, but check you motors manual to be sure.
  • Look at the float level. It should be level when you have the top turned upside down.
  • Check the float drop. Around 1″ depending on the application.
  • Move the float up and down to make sure it isn’t catching somewhere. It doesn’t take much.
  • Check the power piston. It should move up and down freely.
  • Does the power valve pin move up and down freely? Also make sure it lines up with the power piston plunger.
  • Look under the power valve for any foreign material.
  • Check the power valve itself for foreign material.
  • Do you have the correct carburetor on the engine. There are some differences between the Mercarb carburetors that could affect power.
Updated on 12/11/2020

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