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Discussion Starter · #1 ·
Curious to see hear input as to what could be going on...

Came in after 1st session on track, bike stalled coming into the pit with clutch pulled in. At low RPM it stumbles/stalls when trying to start and after running for a minute or so it would shut off. No discernible loss of power on track on wide open throttle or at high RPMs. Anything above 4-6K it is running just fine. As the day went on, it got worse and eventually sounded like it wasn't firing on all cylinders when idling (going back and forth b/w 3 and 4 cylinders). Tried to start the bike again this morning (5 days later) issues still persists which is actually a good thing from a diagnosis standpoint. Currently at 14,220 miles on odo. so I am due for a few major service items, planning on going through the bike entirely and getting it up to date on all its maintenance under this service interval.

Current plan:

  • Check for any codes
  • Remove existing spark plugs and check for spark
  • Wrap stick coils in electrical tape (looking for faulty stick coil that could be breaking down and arcing on the head within the spark plug bore)
  • Replace spark plugs (14K service interval)
  • Check fuel injectors for optimal flow (thought is that at high RPM's there is enough pressure to ensure fuel flow but at low RPM pressure is not able to be maintained and engine is stalling)
  • Check and replace fuel filter
  • Mix and run fuel injector cleaner in fuel
  • Swap MAP and air pressure sensors (rule out failing sensor)
  • Check valve clearances (adjusting if necessary)

All that said.. am I missing anything? Something else I should be looking at? Am I on the wrong track with any of this?

RE the valve clearance check and adjustment... I found and bought a Suzuki factory service manual off ebay a year or so ago (it is for an 04 GSX-R 750 - but the specs are essentially the same) and someone has an excellent write up for the valve clearance check so b/w those two I think I have the information I need. It is definitely daunting but I would like to learn to do this myself and not rely on the dealer.
 

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A guess would be clogged primary injectors but I am guessing and the actual grease monkeys will give you a much better answer. Since it is running weel in the higher RPM range I am going to assume it is not a fuel volume or supply problem. If it were carbed I'd say plugged pilot jets. I am also gonna type the words throttle position sensor & butterflies because I think the smart guys are going to mention them but I don't know the injected wizardry as well as I do the good old fashioned fuel-make-it-happeners.
 

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Also, I moved you to the tech section so the tech Gods will see this.
 
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Last first, checking the valve clearances is pretty easy, adjusting them is much harder. Some mechanical skill and following the manual and it's not too bad. However, I don't think this is your issue.

I'll throw something out there on the stalling issue. My street 750 would start and idle great when cold but once I did a higher power run then back to idle, one cylinder would be dead. If I let it cool a few minutes the cycle would repeat.
(also going back out on three, the 4th cylinder would wake right up as soon as I got back on the power and the bike felt as strong as normal)

It turned out that one injector was actually hanging open slightly and flooding that cylinder when going back to idle. My guess is the higher duty cycle of the higher power run got it wedged a bit harder? I was able to fix it by flushing and cycling the injector with carb cleaner.

At idle there is so little fuel metered so that a little extra will kill combustion as easy as too little fuel.
 
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It turned out that one injector was actually hanging open slightly and flooding that cylinder when going back to idle. My guess is the higher duty cycle of the higher power run got it wedged a bit harder?
I think you can check this. When the issue will appeared on idle, pull up the tank and locate failing cyl by disconnecting the injector wire plugs one by one. When its detected, then connect all injector, and revving again for a minute. Then back to idling and if the issue persist, than stop the engine, twist off spark plug of the detected cyl and check plug fluded (wet, smell).
 

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Discussion Starter · #7 ·
Thanks everyone! Seems I need to add fuel injectors to the list..

Just to clarify..

1. I'm guessing unplugging the fuel injectors one by one will allow me to find the one that when disconnected the engine will stay running or conversely stall out which would clue me into needing to take a close look at that injector?

2. Am I to understand that if one cylinder is not running properly looking at the spark plug for that cylinder I would see more unburned fuel build up vs a cylinder that is properly firing?

3. Without seeing my FI light flashing I would also guess that checking for codes will not net me anything?
 

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1. Yes.
2. Yes.
3. Yes. You would keep in mind that FI light will going on while you will disconnect the injectors, ignore it. FI light goes off automatically when you will connected all injectors at all.
 

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Unplugging any injector is going to cause the engine to suffer. Unless you have one you think isn't working at all and you're looking for no change in operation.

Mainly look for inconsistency in appearance across all four spark plugs. An odd one will identify the cylinder that's the issue. Once we know where the problem is and is not, we can play musical chairs with some parts and pinpoint the problem.
 

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Mainly look for inconsistency in appearance across all four spark plugs. An odd one will identify the cylinder that's the issue. Once we know where the problem is and is not, we can play musical chairs with some parts and pinpoint the problem.
I think so, occasional miss spark of one plug can be a reason. Also as John says the one injector hanging in open state after full throttle operation at wide duty cycle.
Method above would check John's version.
 

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It's much easier to just squirt some water or WD-40 on the exhaust header to find the cool one.

Checking spark is very straight forward and easy to confirm (lay the coil and plug on the cylinder, crank and watch) so if you have spark, then it is a fuel issue.
 
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It's much easier to just squirt some water or WD-40 on the exhaust header to find the cool one.
Yes, you are right. But I prefer to use an IR thermometer (pyrometer) - directing it on each exhaust tube to meter exactly. So many methods to find failing cyl exist, of cose. Then, to check what fail plug or injector we'll could twist of failing cyl's plug and use own nose to smell out failure - gasolone or not gasoline 😁

This is my humble opinion.
 

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Discussion Starter · #14 ·
Alright! So good news and bad news.

Good news is the spark plugs were all fouled out and definitely needed to be replaced. Doing that helped the stumbling/stalling issue. Fires right up and runs on all 4 cylinders without any issues.

Bad news is I am finding that after riding for an extended period of time the engine will randomly stop. When it does the check engine light comes on and if I try to start the engine it will crank continuously but not start. I also noticed that when this happens, the fuel pump is not priming when cycling the kill switch. After about 5-10 minutes, I can cycle the kill switch and the fuel pump will prime and bike will start right back up as if nothing happened.

My guess is the fuel pump is going bad and maybe on its way out. Thoughts?
 

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When the bike stops, does it also show "FI" or "CHEC" in the temp window? Not just the red FI light?
 

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Discussion Starter · #17 ·
When the bike stops, does it also show "FI" or "CHEC" in the temp window? Not just the red FI light?
It does not show FI, just CHEC

I dropped it off at the dealer for them to take a look at. They didn't find anything but the historic error codes were interesting. Two of the error codes are from running the engine with new spark plugs but no airbox. The other was a Fuel Pump Circuit error.

That reminded me... I installed Rizoma turn signals and replaced the factory turn signal relay with one from TST Industries to balance out the flash rate. Is the fuel pump relay integrated into the same relay as the turn signals on the 05 750's? If so, I wonder if that relay is faulting out and causing the issue.
 

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Discussion Starter · #19 ·
Do you have the old relay still you can swap back in?
I kept the factory relay.. dealer wants me to swap the relays and take the bike out for a 1-2 hour long ride on Friday to see if we can get it to fail on the factory relay.

But if anyone knows if the turn signals and fuel pump relay are integrated into the same relay let me know. That might make sense as to what is going on.
 

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I kept the factory relay.. dealer wants me to swap the relays and take the bike out for a 1-2 hour long ride on Friday to see if we can get it to fail on the factory relay.

But if anyone knows if the turn signals and fuel pump relay are integrated into the same relay let me know. That might make sense as to what is going on.
No, the fuel pump relay is separate. The side stand safety relay is combined with the turn signal flasher.

But if the side stand relay fails, or gets flakey, it shuts off the ECM which of course turns off the fuel relay.
 
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