Curvy looses power after 5000 rpm

Ladies and gents...
A friend of mine has a problem with curvy.
When driving there is a loss of power after 5000 rpm bike wont accelerate.

When he does give it rpm on neutral it seems to work.

So far:
- spark plugs seem ok on both cylinders
- no water issues on front
- ignition coils an wires are ok
- gets petrol

Whats next?

Checked, the foamy bit under the tank isn't blocking the Airbox?

I recently rode a CB500 that had a serious oil leak (don't ask). It showed the same smyptoms, a lack of power approx 5-6k RPM and above. Low oil pressure does that.

I changed the oil filter (it had a hole in it!!) and filled it up with fresh oil, and it rev'd happily to the redline pulling all the way.

Just a thought...

If your going in the airbox to change a filter then just stick your finger in the carb bellmouth and make sure the slides are free, big black thingy with a needle stuck out of it. Sounds fuelling, could be a blocked main jet or crud in the float bowls, they're a bitch to drain but worth it, should be done every now and then anyway. 5000 rpm sounds like it should be going over to the mains by then and the sliders coming up. Also try one of them de laquering fuel additives, will help get rid of gumming up of the fuel lines and carbs. While you got the tank up take the vacuum pipe off the inlet and the fuel pipe off the tap, suck on the vacuum pipe, you'll know if it works there should be a really healthy flow of petrol.

[Stu]

Is it restricted?

Originally Posted by Addicted

Is it restricted?

I would love the reply to be, "how do i find that out..."

Gents it was dirt in the main jet of the other carb...
Problem solved.

Cheers
Jussi

Good man! Fit a fuel filter! The crap came from somewhere and a filters only a pound or two