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Hey guys,
I apologize if this is not the right place for this but i assume there is probably not much difference between a gsx f and 600R
Bike 08 GSX650f
Im experiencing a rather strange misfire which occurs mainly at higher loads and RPM.
The misfire tends to happen at 80% - 100% throttle, and is that bad that you will not accelerate
if you use slightly less throttle than where the misfire occurs you can rev it out to the rev limiter cleanly.
And the interesting thing is, say you cruise along in 1st gear at 6k, snap throttle open and it starts to break down. You can flick the kill switch on off and then get straight back onto the throttle and it will pull clean. After a variable amount of time the miss will return.

Ive replaced the voltage rectifier
Fuel Pump
Coilpacks
 

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I apologize if this is not the right place for this but i assume there is probably not much difference between a gsx f and 600R
Bike 08 GSX650f
I'm not so sure about that, as I've never laid eyes on a GSX-F service manual, so what follows will be general comments.

Im experiencing a rather strange misfire which occurs mainly at higher loads and RPM.
The misfire tends to happen at 80% - 100% throttle, and is that bad that you will not accelerate
if you use slightly less throttle than where the misfire occurs you can rev it out to the rev limiter cleanly.
Up until here, this behavior is not very strange. It sounds like a textbook case of fuel starvation, probably due to a blocked fuel filter or injectors. Note that, although you mention having replaced the pump, if that means just the motor itself and not the whole assembly, then chances are you haven't replaced the filter. At least on a GSX-R you wouldn't have.

And the interesting thing is, say you cruise along in 1st gear at 6k, snap throttle open and it starts to break down. You can flick the kill switch on off and then get straight back onto the throttle and it will pull clean. After a variable amount of time the miss will return.
This is more strange. If after cycling the kill switch, you open the throttle as much as before, at the same engine speed as before, and don't get any misfire any more, then that doesn't fit into the fuel starvation theory. It would point to a faulty kill switch, but that would cause trouble all the time, not at higher engine loads only. I therefore suspect this observation is not entirely correct. Perhaps you don't open the throttle as much after flicking the switch, or the engine speed has dropped in the meantime?

Ive replaced the voltage rectifier
Fuel Pump
Coilpacks
Since replacing these has obviously had no effect, I'd recommend reinstalling the OEM parts, especially if they were replaced with cheap aftermarket parts.
 

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Discussion Starter #3
Thanks for your reply

I forgot to mention that when i replaced the pump the problem got a little better, i did some further research and found that theres a filter in the upper half of the fuel pump assembly that houses the fuel reg.
I cleaned it out as best i could and went for a ride and so far the problem has gone away.

I assume flicking the ign let it prime the rail to pressure again so it would run ok for one pull.
 

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I would find a manual and perform a fuel flow test to make sure the pump is pushing enough juice through the lines. Also, you may want to have a close look at the fuel line routing, and condition. Sometimws, especially if replaced with non oem, fuel lines can break down and kink more easily.
 

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I assume flicking the ign let it prime the rail to pressure again so it would run ok for one pull.
Yes, that sounds plausible, if the improvement is for one pull and depending on the way the ECU operates during a moving reset. The on-reset pump prime generally amounts to activation of the pump for a few seconds and this normally happens before you start the engine, but I'm not sure the ECU actively prevents firing of the injectors or plugs during priming; I think it's just that one usually just chooses not to crank the motor, until all the whirring has ceased.

If the bike is moving during reset, I'd assume the engine to start, as soon as the ECU boots up, thus preventing any priming, but I haven't actually ever tried that. When you tried it, was the throttle entirely unresponsive during priming, as if the engine wasn't firing at all?
 
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