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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Hey @WGDaniel ,
Did you manage to fix that? My ROK GP also seems to be limited on 14K😔

If there is no evident issue like reeds, power valve, spark plug etc, it is very likely that you are running too rich. Swap the carb with one of the other karts that are running well and if you see the engine going back to normal, you can then focus on diagnosing what’s wrong with your carb (float level, then check the main jet with the proper tools, even if it says 145, it can be much bigger in reality. Like the other guys may be running a 148 real and you may be at 155 real). If it still runs poorly with one of the other carbs, then you know you need to check ignition, followed by mechanical parts

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