Totally lost now,Please adwise.

[Tompasio]

I own a Gsx 750 es 16v 1983.For about 3 months i have tried to get her to run propely,but she wont go faster then 120 km/h,then she starts to hesitate.I have tried to do as follows:
-Carbs cleaned (totally dismantled)
-Valve clearence checked
-Carbs sync ok
-Fuel level in bowls checked with plastic tube,ok
-Tried to change mains from 120 (original) up to 130
-Tried to raise the needles
-New airfilter
-Changed petcock
-New spark wires and caps (NGK)
-New o-rings in the boots
-New 4-1 Marschall Deeptone
She starts very easy,and run well up to about 120 km/h.
Please help me out. Or can it be a electrical failure?

[Macguyver]

Maybe this will help.

http://upload.wikimedia.org/wikipedia/commons/c/c0/JATO_Bottle.jpg

I am sure with all of the smart people here we could come up with a mount for it.

Barring that, I would check the airbox for leaks.

[spyug]

If the carbs are totally clean and properly synched and the valves are set correctly then its going to be an electrical issue. You seemed to have ruled out all the possibilities in the fuel area so I'd start thinking about coils.

I had a Yammie Virago that would run properly for 15 to 20 minutes but would start to hesitate and not rev fully after that time or even if it were in super hot weather, eventually it would die and not start again until stone cold. I found one bad coil. It worked fine when cold but when heated up the problems started.

I haven't heard of it in GSs but the ignitors can be bad too. Usually it is an all or nothing situation,however.

I'm thinking coils.

Hope this helps a bit.

Let us know what you find.
Cheers,
spyug

[Don-lo]

Electrical would probably show up before 120 km/hr. Since you went to a 4/1 exhaust, I would guess you need to go up higher on the main. The hesitation you mention sounds like a classic symptom. Try 140s and see if it improves.

[Steve]

I agree with the possibility of main jet too small. One way to check: run it up to 120. When it starts to falter, move the "choke" lever a bit. If it clears up and runs better, you are too lean. Adding fuel via the enrichener circuit ("choke") richens the mixture, eliminating your lean running situation.

.

[hikermikem]

Electrical would probably show up before 120 km/hr. Since you went to a 4/1 exhaust, I would guess you need to go up higher on the main. The hesitation you mention sounds like a classic symptom. Try 140s and see if it improves.

I tend to agree with Don-lo - sounds like a fuel starvation issue...

I've had bad coils in the past & once they heated up & failed, it wouldn't start for a while.

How confident are you with the carb sync?

Your post states you "tried" to change the mains & raise the needles - does that mean you did and the problem didn't go away? Or you couldn't actually do either?

I would raise the needles at least one notch (.040") and try 130's to start. Also, make sure there are no airleaks anywhere in the intake system, especially the around the cover of the airbox (may require re-sealing).

[doctorgonzo]

Could be the mains, could be too sharp a bend in the fuel line, or something else interfering with fuel flow from the tank when it needs to really be flowing at max volume too.

[Tompasio]

Yes,I did change the mains from 120 ,122,125 up to 130 an the problem didn't go away.Also raised the needles with no better effect.
Also stock airbox with new sealing.

[jwhelan65]

It has to be a jetting issue? Is the tank clean? you maybe sucking debri into the petcock filter inside the tank. Just a thought.

[rustybronco]

may I see some "good" pictures of your spark plug insulators?

what color does the center insulator show, where it meets the outer shell? (way down deep)

Adding fuel via the enrichener circuit ("choke") richens the mixture, eliminating your lean running situation.

.

good info...