GPz900R refuse WOT in 5th and 6th gear

Ok.. I need help.
Stock 1984 gpz900r, valves are gapped, new ignition coils and caps and plugs
Carburetor operation smooth, good idle, good response, she go to redline in any gear and no problem except when i am in 5 or 6 gear.
The bike hit only 7000 rpm and then wont go over this point.
Alternator is new and is working correctly according to the shop manual.
I have tried another CDI just to be sure but no luck.
Pickup coil resistance ok
New plug wires too
What can i try? Thanks!

I forgot to say i have the stock gearing ratio trasmission

Have you checked the battery & charged it with a good motorcycle charger? and what type of battery is it?
I use a Ctek US 0.8 smart charger & VC97 digital multimeter and occasionally do a load test.

This may not be the same thing you're experiencing. I failed to check the electrolyte level for a number of months one year which included a very hot summer & hot fall. The motorcycle started running poorly at high speeds then would quit. I was able to restart & limp home in low gears and found out that the electrolyte was down about half way. Another time the bike started doing the same thing: the electrolyte was fine, but the battery was shot. It failed a headlight high beam load test. After charging with a good smart charger >> 12.6 VDC. engine OFF >> ignition switch ON & headlight high beam ON >> the voltage dropped significantly below 11 VDC. a good battery should only drop to about 12.2 VDC.

Battery is new. Is a good quality battery, i think this is not the problem

I would still test it with a digital multimeter & do a load test. new batteries are known to be bad or go bad. I had a Scorpion AGM that quit holding a charge after 2 yrs, when they were purported to last 5-7 yrs. I agree that this might not be the problem, but you never know. I check the easy stuff first, just to make sure.



...

Just tested mine. 12.73 volts no load, key on headlight high beam on 12,10 volts

Do you have CV carbs on it (Like Mikuni BS34s) with pods instead of the stock airbox?

No, stock cv carburetors with airbox, new manifold at the intake and between carb and airbox. Filter ok
I think this is not fuel related because if when underload i use the choke lever nothing change in high rpm gear /range.
Im orientend to a ignition problem but i cant understand what.
Cdi swapped and nothing
Tried two set of plugs d8ea and d9ea nothing change
Coils pickup readings are in the spec
The only strange thing on the bike is that the exhaust have not the center pipe that connect the silencers togheter. The PO for some reason has it cut and then capped.

Spark advance moving freely?
Steve

no problem except when i am in 5 or 6 gear.
The bike hit only 7000 rpm and then wont go over this point.

In 6th gear at 7000rpm you'd be at about 170kph - I would expect your acceleration at that speed to be pretty poor on a 34 year old bike.

Does it cough and sputter at the max RPM?
It could be a vibration causing the kickstand switch to get flakey and turning the ignition on and off. It will act like a rev limiter... coughing and sputtering.

I would bypass the safety interlocks and run power direct to the ignition coils etc.

SWest wrote: Spark advance moving freely?
Steve

He should have electronic advance on that bike I would imagine.