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Discussion Starter · #1 ·
Hello everyone.

I hope someone can help me find my problem as I’m completely stumped.

07gsxr 750 20k miles. Runs beautifully up to WOT.

I can be in any gear at any rpm and try WOT and it spits and sputters. I let of 10% throttle and it’s alive again and will run to redline. Only sputters At WOT.

spark plugs are lean so that tells me fuel.

things I’ve done or checked
-fuel pump(Quantam) flow test is 500ml in 10sec
-fuel filter
-back cleaned the secondary filter
-tps is working and set properly
-stva work as it should (removed butterflies to verify and problem remained)
-seafoamed fuel system.
-injectors are not clogged (doesn’t mean the secondaries aren’t spraying tho)
-valves are adjusted within specs.

no FI light. Bike has cat delete and a slip on with k&n filter. No power commander.

bike idles smoothly throttle is very responsive. I can give her the bang bang on the rev limiter as well. Just sputs at WOT under load only.

Thank you everyone in advanced for any information or help ✌
 

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Hey. I would check TPS adjustment as described in service manual. Also I think be helpful check for smooth resistance change of TP sensor when you slow twist the throttle bar from idle to wot
 

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Wow, you've done good things so far but it does sound like a fuel issue.

I'm assuming you did the fuel quantity check with the tank/pump all assembled?

Did you do a fuel pressure check? Low pressure could cause your issue and can be caused by a nicked or mis-placed o-ring on assembly or faulty pressure relief valve.
 

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Discussion Starter · #4 ·
I have not done a pressure test as I don’t have the tool for that. Seeing as the pump dispersed 500ml in 10 seconds I almost felt like the pressure would be fine. However A pressure test is still on the to do list. I did just replace the pressure regulator for shits and giggles and it did not fix the problem. I did try to be very thorough with checking everything and reading a lot of forums to figure out this problem before posting here. So everything I’ve read up on I’ve done and checked hince the reasons for me being stumped

I did mess with the tps and tried to adjust it to the furthest setting down before the little line on the -00 was on the bottom. (I know it needs to be in the middle and that’s where it’s at.) the slightest throttle twist tho the line moves from middle to top.

again with the all spark plugs showing me a lean condition I do believe it’s still fuel related. I just don’t know where at and I don’t really want to buy another new pump when mine seems to be operating fine.

I also believe the secondary injectors are working since the bike has no issue hanging out about 8,000 rpm.

also fuel line is not kinked and shows no signs it ever was.

the only thing that has really stuck out to me is that this is a cali bike so it has the evap system on it. The owner prior removed what appears to be a check valve or something for that hole contraption. On the bottom of the throttle bodies there are vacuum lines thatconnect to that evap system. I did find a write up about it and it shows that that part of the vacuum is actually not a vacuum but more of a breather. Anyways that is the only hose that doesn’t have a home anymore. I’ve read a few forums stating that removing that evap system does not effect the bike.
 

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the only thing that has really stuck out to me is that this is a cali bike so it has the evap system on it. The owner prior removed what appears to be a check valve or something for that hole contraption. On the bottom of the throttle bodies there are vacuum lines thatconnect to that evap system. I did find a write up about it and it shows that that part of the vacuum is actually not a vacuum but more of a breather. Anyways that is the only hose that doesn’t have a home anymore. I’ve read a few forums stating that removing that evap system does not effect the bike
If you run lean this is may be a key. Any extra air/vacuum leaks may pass through those unplugged hoses. Try to plug them and test ride. Good luck
 

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Discussion Starter · #6 ·
If you run lean this is may be a key. Any extra air/vacuum leaks may pass through those unplugged hoses. Try to plug them and test ride. Good luck
don’t know why I didn’t think if that. I will plug and test it tomorrow.

I attached two photos of the hose I’m talking about. (Screw driver is touching the hose leading to the tail of the bike, which loops and comes back down and is sitting open. The other picture shows them splitting and running to the throttle bodies.)
Do you know where the hose runs to on a non cali bike? This hose runs up to the tail to the evap system. From my understanding it’s only on the cali bikes so it must go somewhere else???
 

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Did you check resistance sweep of tps while open throttle to wot?
BTW, Please put some photos of your spark plugs show central electrode insulator.
 

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I would not remove butterflies for further problems of vacuum leakage.:rolleyes:
What I meant was unscrew the butterfly plates. He could test by removing air box and gunning engine while in neutral to see if they fully open, instead of throwing money at the problem without end. I missed the part where he already removed butterflies?
 

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If you already removed butterflies, I would try and strap a mini bungee cord around your kick stand and go for a ride… Your issue may very well be wind resistance at full throttle affecting your kick stand position and not a fuel issue.
 

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Discussion Starter · #13 ·
Thanks for all the replies guys. Yes as stated I have already removed the butterflies and tried and that was not the issue. As far as the kickstand switch goes I don’t believe it is that as it’s just a wot issue in any gear at any speed. The kickstand spring is also in excellent condition as the kickstand has some good resistance while trying to put it down to stand. I will inspect again just to be sure tho 100 %.

since my last post I have checked the resistance in the tps and it shows a smooth sweep between 1.7-4.8 (test performed multiple times).
My buddy had a spare new fuel pump (not assembly) laying around so I tossed it in to verify pump relation and still no change in performance.

also verified again that all injectors are spraying as should be.

only thing I have noticed new now is while riding if casually ridden the f1 light will not come on. The moment you get on to get around a car or have some fun it turns on.

checked codes Again and still -c00

I figured it had to be something with the tps since there is a connection between those two so I picked up a new one since it was only 25 bucks and installed today. Again no change in performance.

here is a picture of one of the spark plugs. Unfortunately my other pictures didn’t save and the bike is back together, I will upload all 4 shortly but they did all look similar.

the next thing cause for concern would be ecu right?

Wood Automotive tire Household hardware Finger Thumb
 

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Thanks for all the replies guys. Yes as stated I have already removed the butterflies and tried and that was not the issue. As far as the kickstand switch goes I don’t believe it is that as it’s just a wot issue in any gear at any speed. The kickstand spring is also in excellent condition as the kickstand has some good resistance while trying to put it down to stand. I will inspect again just to be sure tho 100 %.

since my last post I have checked the resistance in the tps and it shows a smooth sweep between 1.7-4.8 (test performed multiple times).
My buddy had a spare new fuel pump (not assembly) laying around so I tossed it in to verify pump relation and still no change in performance.

also verified again that all injectors are spraying as should be.

only thing I have noticed new now is while riding if casually ridden the f1 light will not come on. The moment you get on to get around a car or have some fun it turns on.

checked codes Again and still -c00

I figured it had to be something with the tps since there is a connection between those two so I picked up a new one since it was only 25 bucks and installed today. Again no change in performance.

here is a picture of one of the spark plugs. Unfortunately my other pictures didn’t save and the bike is back together, I will upload all 4 shortly but they did all look similar.

the next thing cause for concern would be ecu right?

View attachment 299180
Looks like you run rich, not lean.
 

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This has always been my understanding with them. Maybe I’m just use to the two smoker plugs 🤷🏻‍♂️ View attachment 299181
This chart is applicable for old school carbureted cars, it can't applicable to modern FI engines. For modern injectors lean and normal mixture are white color of insulator (top right on this chart).
BTW top center photo on this chart is for engine with weared oil rings or valve seals.
 

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Discussion Starter · #17 ·
Noted. 👍 thanks for the info

well I’m still stumped. I definitely had my fingers crossed on that tps sensor but that was a no go so still at square one considering all that has been changed and checked.

the only other thing I want to try is switch gas tanks with a good runner bike just to totally rule out fuel pump or assembly issue.

if that still has no change in performance then I would have to assume computer..?
 

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It's fuel delivery. Plugs confirm you're starving it. You need a pressure gauge with a hose long enough you can zip tie it to the upper clamp and ride it. I bet you see a pressure drop.
 

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Discussion Starter · #20 ·
Air filter pulled causes a hesitation with a blip and still no change in top end.

If its fuel pressure related then it’s gotta be the assembly itself with the unserviceable filter. Two new pumps and new pressure regulator has not cured the issue.
 
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