Hi Everyone,

I would appreciate if somebody help me to find the firts step for this issue:
Motor runs well in range idle-6000 and 7000-12k but in range 6k-7k there is no power/very week.
I have new air filter, plugs, fuel.

May be caused by power walve, or carburator settings, carb. solenoid ?
What is the best strating point?

Thank you,
Ivan

Is this in any gear?

Is the bike modified?

When did you last service and de-coke the powervalves?

Have you checked cable tension for the power valve drives?

What colour are the spark plug tips?

Also, when did the problem start, was it gradual or sudden, did it coincide with anything.. i.e. changing the plugs, airfilter etc...

Thank you for reply.

By the way, Im just bought this bike, and only replace the necessary. Didn't look inside the engine jet, so i don't know the condition of rc valves, but i will check it if necessary.

I've checked the cable tension, and readjust before test day.
Yes, it's in any gear. (1-2-3 didn't test the others, was a small track)
Checked the lower plug, its nice dark brown and dry.
About modified, what do you mean? I don't think so, its original I think. (nozzles) But if I thinking, one thing with cyliner, it's remaked. I mean, the "inside of cylinder" (don't know the right word, maybe bush) was replaced. But the valve holes and everyting is proffesionaly exact sizing as original. I don't have any tool for measure compression, but its looks good. And as I said, the engine have a great power except that range.

Additional, its weak in any throttle position in that range.

Thanks,

Ivan

Dave Ett wrote:Is this in any gear?

Is the bike modified?

When did you last service and de-coke the powervalves?

Have you checked cable tension for the power valve drives?

What colour are the spark plug tips?

nobby62 wrote:Also, when did the problem start, was it gradual or sudden, did it coincide with anything.. i.e. changing the plugs, airfilter etc...

So, i've just bought this bike without test drive (it was unserviceable). It was in garage five years ago. So, i dont know the original driving properties.

Try putting your hand on a carburetor and rev it up to see if there is excess vibration at the carby in the 6-7k rpm range.
Perhaps excess vibration is causing the fuel in the float bowl to become frothy over the 6-7k rpm range?? and affecting power??

If the rubber carby mounts have hardened over time, they may now not be very good at isolating the carby's from engine vibration.
This is just a wild guess. It could easily be something else causing your problem.

remove the airfilter and see if there is any difference

Hi
If the bike was in a garage for 5 years as you said.
You should immediately clean your carbs with a good carb cleaner spray and pay very attention at the slow jets and emulsion tubes which they have the smallest holes.