Runs like crap

[Rcmxchamp]

Hey guys I'm new here I've always owned gixxers buy now I have a 2001 katana 750 when I leave the fuel switch in the prime position it runs ok but when I get up into high rpm even around 9 it runs like crap and when I turn the fuel switch to the on position it acts like I'm running out of gas and it runs bad to any suggestions. Thank you

[ManQu]

"PRI" is for refilling the float chamber of the carb after running out of fuel or carb cleaning.
"ON" is normal running. Always use "ON"

The fuel switch has a vacuum valve that opens when the engine is running. This is to stop over filling the carbs. If the carb float needle and seat goes faulty it will fill the engine with fuel.
So when in "PRI" this bypasses the valve to refill carbs and can cause engine filling.

[Rcmxchamp]

Thank you I understand that my question is why does it run good in prime but when I turn it to the on position and I'm driving down the road it's acting like I'm running out of fuel and when it's on prime or reserve it runs like crap up at high rpm

[Aimbot9000]

the vacuum valve could be bad in the petcock or the vacuum line either not attached or is damaged and not holding the suction. try replacing the hose first (cheaper) then a petcock rebuild kit.
unrelated but while you're in there check the tank for rust and deal with that while you have things apart anyways.

if i remember right the PRI position does not flow as much fuel as the other positions which would explain the crappy running when you open it up.

[kevin2502000]

Thank you I understand that my question is why does it run good in prime but when I turn it to the on position and I'm driving down the road it's acting like I'm running out of fuel and when it's on prime or reserve it runs like crap up at high rpm

The petcock needs rebuilt or you have a bad vacuum line.

[Rcmxchamp]

Ok thanks for ur help I will try that I won't be able to get to it for a week or so would it be ok to run in the reserve position until then and change the fuel filter while I have it apart or will that get gunk somewhere else too?

[kevin2502000]

Ok thanks for ur help I will try that I won't be able to get to it for a week or so would it be ok to run in the reserve position until then and change the fuel filter while I have it apart or will that get gunk somewhere else too?

I just re-read your post, I mis-read thinking it only ran good on Pri. It could still be the pet-cock but easy to test. When you pull your tank off to change the fuel filter, test it. If fuel only trickles out in on or res position when vacuum is applied to the vac hose, it's bad. It should not flow unless vac is applied. Pri should free flow. It could be as simple as your fuel filter needing changed. Next step might be carbs needing cleaned if the other 2 didn't remedy.

[arsenic]

Next step might be carbs needing cleaned if the other 2 didn't remedy.

Okay, I've been silent in this so far, but I think dirty carbs should be first and foremost. While a pet cock issue may exist, the carbs need to be dealt with, 100%.

[Rcmxchamp]

Thanks for all the help guys I will try it all but would it be ok to run it on reserve for a week or a little more?

[arsenic]

What gave you the idea that running on reserve is going to make anything better? It's the same as on, it relies on vacuum. Reserve just sucks gas lower in the tank. So if you have any rust or sediment in the gas tank, it will now be in your carbs.

[Rcmxchamp]

Nothing gave me that idea that's why I asked that question because I didn't know I've always had fuel injected bikes before this

Ok so last question I think guy and again thanks for all of your help will it be ok to run on prime for a week or a little more until I can get this situated

[arsenic]

Okay, I thought someone said it was a good idea. It is not.

[Rcmxchamp]

Thanks everyone

[Rcmxchamp]

Ok guys its all fixed ended up being a bad petcock but that wasn't causing it to run bad it was whoever worked on the carbs last out some caps on wrong and it had a air leak also someone but the battery holder on wrong to where it was covering 3/4 of the air port hole all fixed now though and runs great thanks for all your help guys