So you guys think just changing the plug and running 93 in it or running racing fuel in it? Thanks again

 

I dont think 93 octane is needed, certainly not higher.
Sounds like its going lean, in the upper throttle positions. Try a test run with the choke on, or with a piece of duct tape, covering about 1/3 of the snorkle opening. This will richen up all the circuits, and if it runs better at 1/2 to full throttle, then you need to look for reasons its running lean. Such as low float level, plugged main jet or passage,plugged fuel filter, air leak, to much alcohol in gas( if your not using pure gas).

 

90 octane is recommended for the Z. I like to add a little octane booster to 90, just to make sure, but it's not necessary. 90-91 will do.

 

Ok guys I changed out the spark plug today with a new one and put a new air filter on it just in case. Still no help here. I talked to the dealer about this and they said no to the racing fuel like you guys and suggested it could have something to do with carb. Any other ideas?

 

You seem reluctant to believe its a jettting problem.
Have you removed the float bowl on the carb, and looked for crud in the bottom of it? Im thinking the main is restricted, that will effect the running from 1/4 throttle on up.
Heres an easy thing to try...put some duct tape over the intake snorkle, for a test drive. Cover the opening, by about 1/3, then go for a ride. If the sputtering goes away or gets better, then the bike has a lean problem. Covering the intake, will make it run richer.

Heres a link to sites which covers carb cleaning.

carb clean
carb clean 2

 

Thanks. I'd forgot to check this.