81 KZ750e wont rev past 7k

CRAP: Sorry i posted this in engine instead of carburetors

Hi guys, have an 81 KZ750e with Wiseco 810 kit installed with K+N clamp ons and 4-1 Kerker. Bike has about 5000 miles since the kit was installed, but it sat for a few years prior to me picking it up about two months ago.

The bike received an oil change,new battery, tires, complete carb cleaning/rejet/sync and tune up right before I got it. I've got about 1000 miles on it since purchasing and have run about 5 tanks of B-12 chemtool through it. She runs like a champ up to 7k at all throttle positions, but my issue is it really doesnt want to rev past about 7k rpm. If i'm at WOT it really won't do it. IT almost acts like there is a rev limiter in place, kinda stutters a little but mostly feels like it just doesn't want to go. I noticed the K+N clamp ons were dirty, so I cleaned and re-oiled. They were pretty dirty and dry as a bone. The bike seemed to want to rev a little higher after that but not much, so I'm guessing that the mains are a little rich?

Also, I have a little popping on decel with the throttle closed, so I'm going to back the pilot screws out a 1/4 to 1/2 turn to see if that helps.

Thanks everyone!

Check that the fuel line, from the tank to the carbs, doesn't have a tight bend or kink in it. I had the same problem after rebuilding the carbs on my 650. Kink in the fuel line had it starving for fuel above ~7500, for me... cutting 1/4" off the line and the problem was resolved.

Might be an incorrect fuel filter. A filter made for a pressurized system (with a fuel pump) will not flow enough in a gravity feed system. Might also be trash clogging the filter screen on the petcock. I wonder if a sticking timing advanced could do this?

Maybe try lifting the needles a notch if they are adjustable, or shimming them. That will richen the mix and might be interesting to see if it improves things at all.

Is your ATU advancing fully? get a strobe onto it and check for full adcvance -they can seize up.

all great ideas and simple things to check (minus moving the needles lol) , thank you everyone. I will start on this in the next few days and let ya know what I find. I wondered about timing too, as my other points ignition bikes had similar symptoms when the point timing was off. The inside of my tank is due for a cleaning so the screen on the petcock may indeed be clogged.

Hey Mikey... (he likes it! ...sorry, couldn't help myself! (o:)

You may also want to consider putting an inline fuel filter in place, if you don't already have...

Sounds like a jetting issue. A lot guys mod their bikes without taking care of the jetting properly, and problems like this show up. Hopefully the jetting hasn't damaged the engine by making the engine run super hot. Another thing is to verify the valve adjustment, which is another thing that's chronically bodged. Failing to perform maintenance tasks such as this destroy the engine so it's always best to check with each new/used bike purchase before you rub salt into a possible wound.

Nessism makes a good point about checking ALL the routine maintenance items. Just because someone said it was done, doesn't always make it so. No combinations of jets and needle positions can fully compensate for bodged basic maintenance.

good idea: I'm picking up a manual soon so I will check valves at that time. I have to replace the valve cover gasket so it would be a good time for it.

I still haven't had a chance to look at my stinkin bike, but I will try this weekend. damn 30 hour shifts and nursing school. Ugh. Really cutting into my riding LOL.

Ok I checked my peacock screen and it's good. No real crud floating in the tank. This is what I did find: the fuel filter has 1/4" inlet/outlet and the fuel tubing is 5/16". I'm guessing I'm having a bottleneck going on when I'm wot. I'm headed to summit racing this afternoon to pick up a fuel filter with 5/16" inlet/outlet and will report back...

I also had a problem like this u said bike carbs were tuned...if the new filter or petcock don't help u out make sure the float Heights are right... Cause first time I did my carbs I adjusted the float Heights level like manual told me to but in fact the carbs were not level on the bike so my carbs kept starving...