Jetting question

[lech]

I have some trouble with my daughters trial bike, When she is going on low rpm and give full trottle it just goes mooh..
If you pump the trottle a little bit instead of full trottle no problem.
What is causing this ? To much fuel or air.
Have tried changing jet and needle position but as I am not sure what causing the trouble it would help if any clue.
Bike is a Beta Rev50 and runs fine except from this.

Thank's
Lech

[bergerhag]

I'd guess too lean. Try the same manoeuver while applying some choke. If it runs better, it is likely too lean. What carb is it?

[lech]

Carburator is Dell'Orto PHBG 19.
Thougt it was to lean and have been able to get it better by changing needle possition and mowing airscrew but not as goods as I want.

Will try the choke thing.
Thank's for your reply.
lech

[bergerhag]

Also check your float level, the float bowl air vents and that fuel flow to carb is not restricted by filter in carb inlet or at the tank fuel tap. Also check that the fuel cap air vent is not clogged or restricted.

I assume you have performed a thorough carb cleaning?

Needle position should not make any noticable difference when doing a very sudden wide open throttle off idle. Only main jet and fuel level in float bowl would affect that.