gpz 750 stays at 5000rpm after reving

hi guys....i am new here and i need help badly cause i am out of ideas....

here is a story...

My 1983 gpz 750 uni trak with 0.50 fresh overbore engine, 4-1 exhaust with STOCK carb settings and stock air box after warming up and reving it a little bit does not drop to idle (keep it at 5000rpm and doesnt drop down)
i checked everything
1.throttle works normaly...no sticking....
2.rubbers between head and carb...new....rubbers between carb and airbox ...new
3.pilot screw 2 and half turns out
4. valve settings all in specs
5. done the synchronisation of carbs with gauges

it works normally until the 4000 rpm and lowers the rpm....after reving it to 5000 it stays there and i cant get it down to idle...i checked for air leaks with spray but no changes in rpm.
i changed the carbs to my other gpz 750(everything stock on it) it works even better with those carbs.
Changed 3 sets of carbs...all stock all do the same thing...changed airbox to other one...still same...

everybody says that i have air leak but where and how to find it?
any suggestions cause i am going nuts here

Timing advance weights sticking causing the high idle
Behind small cover on the right side of the motor, should be 2 bolts to get cover off, check and see if the weights are springing back or are they a little rusty, lubricate accordingly

Check this, I had the same issue with my 550

I dont have atu unit...just rotor and 2 little magnets so thats not an option...

sorry I thought it had a mechanical advance

if there are no leaks then I am out of ideas

Pics of your rotor and pick ups?
Steve

Here....rotor and pick ups

Little update....i found that it has cdi unit from kz 750 engine...does it matter?
Ill try to swap and see what happends

Stillingnesk wrote: Little update....i found that it has cdi unit from kz 750 engine...does it matter?
Ill try to swap and see what happends

That's an ignitor, not a CDI. At any rate, the early 750 bikes had a mechanical spark advance so the ignitor is designed to work with such.

head milled....cylinders milled....leaks from the new head gasket
ill update u guys after disassembling...i hope its not cracked head

Just so I understand - you can get it to idle, and it can rev to 4000rpm fine, but if you rev it to 5000 rpm, the revs don't drop back down?

The way I see it, for the engine to maintain 5000rpm it needs to be getting enough air/fuel mixture to keep spinning at that speed. Surely it must be carburetor related? It could be your butterfly sticking, or as simple as your accelerator cable need lubing.

With throotle cable or without...same issues....changend carbs with another ones...same issues....
One interest thing...i have sprayed with brake cleaner arround head gasket....and it changed rpm...everybody said it has leaking head gasket...
Just out of curiosity...i have done it to my other perfectly good kawasaki gpz 750.... And almoust stalled it with spraying.....

Looks like breake cleaner produces very cold affect to cylinders wich affects carb mixtu
re...
I couldnt belive that it could have that kind of affect