help pls

I have put the carbs back on my kz750 spectre with the floating height
set at 21mm (per the factory manual specs). It starts and Idles fine, but at around
4500 - 5000k it spits and drops rpms rapidly. Any suggestions??

what else has been done to the carbs?

Not enough fuel?

Check tank vent or petcock.

Do you run a filter?

Try these for a start.

I have put in a set rebuild kits, cleaned everything with carb
cleaner and used Brasso. The only thing I haven't done is
put on the tubes into the breather box.

I will check fuel level in bowels next. I am using an
external glass filter.

Try running it without your external filter.

Oh, and run a can of seafoam through your tank. I get lucky a lot of times with this stuff when my carbs are being tempermental. Nice fix for under 10 bucks.

Ok, without the external filter i can get it up
about 6k rpm and it drops back down. Any
more thoughts??

what bike?carbs?

Is your gas cap clean?
It is your vent.

How about the petcock?

Had a to small of a fuel filter on my first KZ1000.
It would run the bowls dry after sustained high rpm.
Also run a barrel valve (hardware store) instead of a petcock.Requires some welding and fabrication.

Bike is an '82 kz750 spectre with keihin cv34 carbs which I have
rebuilt, cleaned and set the floats to 21mm per factory manual.

I have taken apart the petcock and cleaned it out.

I don't know what else to do, except take it to a shop.

reaver573 wrote:

I have put in a set rebuild kits, cleaned everything with carb
cleaner and used Brasso. The only thing I haven't done is
put on the tubes into the breather box.

So your running cv carbs without the velocity stacks??? If that is the case, get the boots on and the box sealed up properly and your problem should go away.

reaver573 wrote:

I will check fuel level in bowels next....

Great idea. And should perform clear tube test to determine actual fuel level inside float bowls.

The fuel level is far more critical than float height.

Setting float height to specs may get in the ball park, but often fails to result in correct fuel level.

Good Fortune!

Patton wrote:

reaver573 wrote:

I will check fuel level in bowels next....

Great idea. And should perform clear tube test to determine actual fuel level inside float bowls.

The fuel level is far more critical than float height.

Setting float height to specs may get in the ball park, but often fails to result in correct fuel level...

Yep. For me setting them dry was a complete waste of time.