Low RPM on 125CC ROK GP

I have a Vortex 125CC ROK GP on an OTK 401R that will only go up to about 13,600 RPM. 11/72 sprocket, 108 chain, 145 main jet, needle notch at the 2 position. I’ve cleaned the carburetor and changed the plug numerous times with no luck. We have three other OTK karts with the same ROK GP engines and setup witch get up to full RPM and speed no problem. What am I overlooking?

How does your minimum RPM compare to the other karts? ie is your driving comparable to the others?

Could it be time for an engine service? Cracked reeds or low compression would cause low performance.

Blocked exhaust is another thing that can catch people out.

Sliding axle or binding brakes will sap power, but generally you’ll notice your brakes are pretty hot when that happens too.

Thanks for the response. The kart/engine is new with about three hours on it, our group are all fairly close driver skill wise.

It seems to pull strong and be equal to the other karts, accelerates well up to 13600 and then just hangs there.

If exhaust blockage could it be the power valve possibly?

Nothing obvious with brakes or any rubbing/dragging.

Check the power valve operation.

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Same model of coil ?

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