Hello, I have a Beta Rev 80 which is surging/cutting out at high throttle/WOT. It is stalling for amoment, then picks up before stalls again..

I have cleaned carburettor and nozzles, i have checked float level, tried changing needle positions, changed gasoline and ensured fuel supply is ok. Changed spark plug. Checked air filter.

I have no idea what can be the problem. I have not checked ignition timing, i dont even know how the ignition works.

Any tips wold be appreciated, i still suspect the carburettor float or similar.
Regards Oddemann

Edited September 20, 20196 yr by Oddemann

Did you change out the vent lines, or pinch the vent for the gas cap?

6 hours ago, lineaway said:

Did you change out the vent lines, or pinch the vent for the gas cap?

The vent lines and gas cap is ok. I did also ran it without the vent lines.

Is there a way i can verify the function of the float bowl ?

Carb off and clean, tube attached to fuel inlet, gently blow using mouth into tube. Hold carb upside down, repeat blowing action....you should feel resistance to your air pressure.

Float bowl off, repeat using a finger to gently lift float up....I’m guessing the float is attached to the carb and not sited in the bowl.... and lower the float allowing air in and stopping as you move the float. If the float is bowl sited then make sure any guide posts allow the float to move up and down smoothly. You will need to find actual height setting specs from the manufacturers manual. 

If the crankshaft oil seals are worn then this will allow a loss of crankcase compression and mixture which will affect engine performance and this is where I would be looking. If you can pull the crankshaft in and out by much then you may have worn main bearings which will load the oil seals more causing fairly rapid lip scoring. This will allow both air in and out while the engine is running.

As a final few points to check as you seem to have covered most everything else, poor compression, badly worn cylinder bore, partial seizing...oil mix ratio+cooling issues. All can create similar symptoms to yours as described?

You may also have an ignition coil that is breaking down under load eg cant produce sufficient energy at high revs to keep plug sparking. 

I have concluded that carb and fuel is ok. Also compression is ok. I suspect the stator is malfunctioning and will order a new one. Then report back :-)

3 hours ago, Oddemann said:

I have concluded that carb and fuel is ok. Also compression is ok. I suspect the stator is malfunctioning and will order a new one. Then report back ?

Hope you are right with that choice?

Changed the stator today, and now it runs properly, and i am quite happy with that!

And this seems like a common problem on beta. 

Regards
Oddemann