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Discussion Starter #1
Hello to everyone, new member here
so i have a 2009 Gsxr 750. bike has 9500 miles
list of mods: Two brothers slip on, set valve removed, cat removed, k&n intake air filter, and PC5
the bike has been professionally tuned at a local powersports shop mainly for suzuki sport bikes. bike has been dyno tuned to produce 140 hp to the rear wheel. bike feels like a rocket. i am having a major problem. The other night i was going to my gfs house on the parkway, average speed of 90 mph. i stopped by a gas station and got premium 93 gas. i left my girlfriends house around 2 am. it was around 84 degrees. took the parkway down to another main parkway, average speed of 150 mph. upon slowing down to get on ramp to merge to the second parkway, my bike started to sound like a Harley. sounded like a heavy misfire. i pulled over and it wasidling very rough. barely any power. i tried revving it and it hesitated to go above 4k. i rode the bike home about 14 miles doing 70 and cruising. i decided to bring the bike to my shop, were auto repair mechanics, and the bike was still shitty. passed 8k rpm, the bike takes off and no issues. under that, it idles bad and runs rough. i checked plugs, coils, fuel pump, fuel filter, pair valve, tps sensor -C00, goes up when i rev slightly. i removed injectors and cleaned them. checked plugs for spark. NO FI light is on. tested coils. i am stuck at this point. i tried switching back bikes ecm and removed pc5, still did the same thing. i have no idea what the problem may be, any help will be appreciated. thank you in advance
 

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Did you by some chance get a bad batch of gas? It does happen . Is any fi light on ? Did you run a compression test on the motor? Are all your cylinders firing?
 

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Discussion Starter #3
It definitely has to be a batch of gas. Before that the bike was running strong. I emptied the tanks. Pulled fuel pump cleaned that out. Flushed out fuel rail and injectors. Didn’t check compression but bike runs smooth after 8k in all gears. No FI light on. Put fresh gas in and it’s still the same.
 

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So it runs perfect than runs poorly and no power than runs perfect again?

What do you mean by "heavy misfire"? Backfire? Or just cylinder loss?

It would be great if you could catch it while it is doing it and see if one or more of the cylinders were off line.
 

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Discussion Starter #5
So it runs perfect than runs poorly and no power than runs perfect again?

What do you mean by "heavy misfire"? Backfire? Or just cylinder loss?
It ran perfect before I got the gas. Then it ran like shit. It’s been running like shit but It idles fine at 1200 rpm. It runs like shit up until second injectors kick on after 8k rpms. It backfires once every few minutes. It feels like a misfire when I rev it around 3k rpm. I’m sorry if I don’t make sense
 

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It idles fine by itself at 1200? Or are you holding the throttle open to achieve that?

I'm trying to figure out if one cylinder is not firing from your description. The idle drops a couple of hundred rpm with one cylinder out but you have an automatic idle control so that could be compensating.

The best guess is that you have one primary injector not working correctly.

Start the bike up cold and check each header to see if one is noticeably cooler than the others. You can squirt them with a water bottle to see the difference as they get hot really fast.
 

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Discussion Starter #7
It idles fine by itself at 1200? Or are you holding the throttle open to achieve that?

I'm trying to figure out if one cylinder is not firing from your description. The idle drops a couple of hundred rpm with one cylinder out but you have an automatic idle control so that could be compensating.


The best guess is that you have one primary injector not working correctly.

Start the bike up cold and check each header to see if one is noticeably cooler than the others. You can squirt them with a water bottle to see the difference as they get hot really fast.
Idles by itself at 1200. Start up is normal. Whether it’s cold or warmed up, if I twist the throttle to 3k rpm, it goes prrrrr which sounds like one is misfiring. I will check the temps tomorrow when I get to the shop. Didn’t think of that. Thank you
 

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Discussion Starter #8
It idles fine by itself at 1200? Or are you holding the throttle open to achieve that?

I'm trying to figure out if one cylinder is not firing from your description. The idle drops a couple of hundred rpm with one cylinder out but you have an automatic idle control so that could be compensating.

The best guess is that you have one primary injector not working correctly.

Start the bike up cold and check each header to see if one is noticeably cooler than the others. You can squirt them with a water bottle to see the difference as they get hot really fast.
all 4 are around the same temp give or take 10 degrees. tested cold and warmed up after 5 mins.
 

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all 4 are around the same temp give or take 10 degrees. tested cold and warmed up after 5 mins.
But still running rough/poorly while you did this check?
 

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It starts and idles nicely initially, but when you add throttle it sure sounds like it is going to 3 cylinders.

If it was my bike, I'd start it up and go to that rpm for a minute then check the headers again for a cooler pipe. It has to be a different temperature.

Finding the problem cylinder is the first step to solving the issue. My guess is that you are going to find a partially clogged or sticky injector on that cylinder.
 

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Discussion Starter #13
alright ill try the temp reading again. maybe i missed something. also, i pulled all 8 injectors and cleaned them. manually sprayed them to check the angle of spray and it has the V spray. probably still continued after cleaning them
 

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I was assuming from the video that the miss is very consistent, ignition problems generally are not.

That is why I suspect fuel.
 

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Sounds like a plug arcing out to ground to me. Closely inspect your plug boots. Might be lucky it just a bad plug, like the broken one in your hand :/... Hope the other end comes out easy with a screw driver. Good luck...
 

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Not good. There were a few posts of spark plugs breaking in that place about a year ago, nothing recently.

Is that an "NGK" plug? There have been some threads floating around about counterfeit NGK plugs and I wonder if that is not one of them?

PLUG STUDIO / NGK
 

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If the spark plug screwed in easily (hand torque) all the way till the gasket seated, the threaded shell should come back out easily with an easy out.

If you had to use a wrench to seat it, it may be a lot harder.
 

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Discussion Starter #19
Sounds like a plug arcing out to ground to me. Closely inspect your plug boots. Might be lucky it just a bad plug, like the broken one in your hand :/... Hope the other end comes out easy with a screw driver. Good luck...
even with the new plugs, the misfire still happens. but it did get better. im thinking it may be a coil but it wouldnt explain how it smoothes out at high rpms 8k+. i gotta test them again. the plug boots looked good, no cracked or white marks. im baffled
 

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Discussion Starter #20
Not good. There were a few posts of spark plugs breaking in that place about a year ago, nothing recently.

Is that an "NGK" plug? There have been some threads floating around about counterfeit NGK plugs and I wonder if that is not one of them?

PLUG STUDIO / NGK
i hand tighten this and then torqued it, it was 10 ft lbs of torque which i dont understand bc it went all the way in. i didnt try to over tighten it or anything, just twisted till it stopped. they might be fake tho but i got it from a reputable source.
 
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