GPz750 won't rev over 8,000 rpm?

Hi Folks, I have my 1985 GPz750 working very good, however it seems like the rev limiter kicks in at 7,500 RPM.
I've tried a few sizes larger main jets with no difference, 115, 120 & 125.
Plenty of power up to 7,500 RPM, then it drops off. When I back off the RPM to below 7,000 the power comes back on.
Is this a problem with the Igniter? Part number 21119-1069

Do you have the Original Airbox? Without it, isn't going to happen. There is No rev limiter on these older machines, just lack of restriction. 

Thanks and yes I have the airbox in place.

I would start swapping all electronics, one at a time.

Thanks, I agree.

Have you checked the ignition advancer to be sure it is working? Rust or old, dried up WD40 can gum them up.

Could also be bad diaphragms in the, carburetors, preventing the needles from lifting fully.

Personally, I prefer to test and confirm that components are bad before replacing them.

There is a factory service manual in the file base. It describes quite a few testing procedures.

I agree with TexasKz.  Get a FACTORY service manual and start troubleshooting.  I have a ‘83 version and it does not have an advance mechanism on the crank, just a rotor.

Go through everything methodically otherwise you may be throwing unneeded money at it.
What do the spark plugs look like?  Are the jets you’re using genuine Mikuni?  Aftermarket fuel filter? Clean screen at the fuel tap?  Float height set correctly?  Yada yada yada….

Later, Doug

I'm way past beginner suggestions my friends, thank you anyway.

Buffalo BiL wrote:

I'm way past beginner suggestions.

I have ZERO idea what you have or haven’t done other than you still have a stock airbox and you’ve tried different main just sizes per this thread.  Hence the questions.

You can either help us help you or start throwing stupid money at parts it may not need.

Sorry if i come off as rude, but don’t ask for help and then ignore it.

Later, Doug

 

Plug chop it.
 

No canned answers ya say ha. Have to ask, did it ever run correctly during your possession of it? Probably won't apply but years ago i did a set of the stock BS34's for a Friend. It too was all stock KZP1000, wouldn't rev to redline. He too kept going up in main jetting to no avail. Come to find the stock exhaust 4 into 2 had rotted baffles and were blocking off exhaust output. Pipes from the outside looked almost new too! See, that's not a pedestrian answer. 

Thanks for all contributions my friends. Just for background, I have been re-fixing motorcycles for 20 years and before that cars since the late 70s. I buy repair manuals too.
This GPz I'm tuning is new to me, and had been in storage since 2008. It needed a lot of work. The PO installed pod filters and 4>1 headers.
I installed an OEM airbox complete with a Uni foam filter, and new slip on muffler.
I only have 350 miles on the bike since restart.
Right now I'm testing with 115 main jets and it seems to be reaching 8,000 RPM. Maybe it's over jetted and flooding out?
After testing it for 100 miles, I'll try 110 main jets.
Next option will be replacing ignition coils.
Thanks