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Discussion Starter #1
Today I was out for some rides. Temp was 50+. First ride once I hit 3rd gear and up, I noticed the bike hit an acceleration wall between 4500 and 5,000 rpms where slowly rolling on the throttle produced laggy acceleration. Even when the bike got to at least 170 degrees and higher rpms, the performance was loagy. I road about 8 miles.
Bike sat for about 15 min., and the next ride of 8+ miles it ran like a top. What could cause this? My gas mileage is still down around 32 mpg because of no interstate riding this tank full. Usually my mileage with this riding was 38, and 45 if I had a bunch of hgwy. Miles.
Still no FI light, plugs and air filter are fine. When I cleaned the injectors they were fine. Coils tested perfect in the resistance tests. I get same performance if I unplug the O2 sensor. EXCA motor is unplugged, and SET valve is wide open. Thanks for the help!
 

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Discussion Starter #3
One thing I corrected a few weeks ago was the TPS, the hash line was at the bottom. At that time I believe the bike was also running lean. Maybe not from the TPS, but I was still getting a slight pop when shifting at higher rpms. (Jardine GP1 straight pipe out of CAT). I believe the bike constantly runs rich now because of the slight rich/gas smell in the exhaust, poorer gas mileage, and when I rev it up it just sounds like an engine running rich to me.
No real smoke in exhaust, and pipe is definitely not excessively black.
 

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Having replaced 7 STVAs on 2x of my GSXRs 2002 and a 2011. I would say your in the right area. TPS adjustment was a good find because it tells the STVA what position it needs to have the top butterflys in. The STVA in general could be going bad which on all of the ones that failed on me they ended up staying completely closed and limiting the bike to about 86mph regardless of gear or how much throttle I gave it. My 2002 never gave me a code for it but my 2011 so just look for the FI (Fuel Injection) code (C28) on your speedo.

As for the running rich problem, if your not getting enough air, lets say due to closed throttle bodies then it can run rich which I have seen. A pop doesn't tell anything about a sport bike or any engine for that matter unless its a lot of pops during specific acts like letting off full throttle,a bike running lean,a pair valve mod, or the removal of a catalytic converter. If you are getting 32mpg I wouldn't say your gas mileage is bad considering my 2011 gsxr 1000 with all of the mods and custom map would yield me 108 miles for 4.5 gallons give or take. Also, I have never heard anyone diagnose a rich bike by the sound so if you could clarify that please do. If there is no smoke/black exhaust especially when you give it full throttle then you don't have any issues. Don't let your butt dyno trick your mind. This is a sport bike and not a GZ250.
 

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Discussion Starter #5
EVL 750. Thanks for the input. I guess the "sound" issue I mention could just be the GP1 pipe, but compared to when I got the used bike last summer, it just doesn't seem to rev as peppy as it did. To me, it sounds more restricted most of the time. The wall I occasionally hit with the acceleration is real. One day I accelerated up hill from a light, and first gear was ok, but at around 5,000 rpms second gear was a dog and actually bogged down some. When the bike has performed like this and I have tried "B" mode to see what that is like, the engine is really bogged down or supressed, way more than it is supposed to be. I have no codes. Is there a way to see if the butterflies are opening properly? I know to see them the air cover would have to be off.
 

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I just wished there was a way to make stva is fully open at top end of rpm or be able to adjust them like tps
 

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Just take the top of the airbox off and watch them from cycling the key to giving it full rpms. They should cycle to about 10% open for a cold start then as you give it throttle they will move back and forth depending on your throttle. If it is a Keihin STVA there is no way to fix it as it is a stepped motor if that is your actual problem but you wont know until it dies. My 2011 gsxr 1000 would run perfect 1 moment going all the way to redline then the next it wouldn't go past 85 in all gears. eventually the motor just died and said C28. I bought a used set off ebay then sold the bike a year later.

Aside from watching the butterflys and taking the airbox top off you can unplug the motor (STVA) which is usually a white 3 pin connector and manually moving the butterflys with your fingers inconjuntion with your throttle to see if you can achieve redline or simulate your problem.
 

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You can disconnect the stva motor and safety wire the top butterflys open (some people even remove them), then adjust your idle down.
 

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Discussion Starter #9 (Edited)
I just took the top off my air box and took a little over a 3-minute video of starting the bike from cold (bike not started for 2 days, temp in 50's) and letting it warm up to 127 degrees. You can hear what it sounds like when I start the engine and shut it down. When I turn on the key, the top butterflies open fully then close. I start the bike and all the way up to 127 degrees the top butterfly stay shut unless I rev the bike up. Any advise?
https://photos.app.goo.gl/QPEbCCGk1pYzCJUz8
 

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Your photo didn't work. When you rev the bike do the butterflys open or do they stay closed? Usually when its idling the butterflys will go from closed to open which is about 10%.
 

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Discussion Starter #11 (Edited)
That's weird. When I click on the link it opens right up on my phone.
To answer your question, when the engine starts, the butterflies stay closed. They are not open 10%. As I increase the throttle they open smoothly. When I rev the bike to 6,000 the butterflies open almost all the way, then close again as rpms decrease.
 

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Discussion Starter #12
Since my secondary butterflies stay closed at idle, is this something I should adjust do they are at 10% open? Would that improve my off line power? When I rev the bike up at idle the first rev goes up around 4,000 (I don't go too high and beat my bike), but the second blip gets it to like 6,000 and sounds much better. I'm guessing that second blip is starting while the butterflies are still slightly open.
Remember I have no codes and the TPS is showing in the middle.
 

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Discussion Starter #13
I read a thread Chuckster responded to several years ago where he said the secondaries should fully open during warm up, then operate with the throttle. Mine fully open then cycle closed. Does that mean the secondary sensor is bad? I can't afford an expensive replacement if that's the case, so what would the next best thing to do or try?
 

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No, the newer bikes behave differently because of the IAC valve. They don't need the fast idle control function that the STVA provided in the past. If you're sure your SET is wide open, and you have no FI code, then I'd say it's a fuel pump issue. You need to do a volume delivery test, and if that passes, do a pressure test.
 

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Discussion Starter #15
My set valve is unplugged and the wire removed from ecu, so no vodes. Cable disconnected from valve which I wired wide open in case the spring failed. I did a pressure test a few weeks ago and got a steady 46psi. Last fuel flow test was about 9 oz. In 10 seconds. I can do both those again tomorrow to be sure.
 

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Personally I wouldn't suspect a fuel pressure loss for 1 specific rpm stall. Since your TPS shows in the middle I would still suspect the STVA to be in the beginning stages of failing. Your top butterflys should cycle open then rotate mostly closed so there is no air gap between the disk and TB wall. I have seen motors completely fail which will go completely horizontal at idle and never move, but like mine and most others the stepper motor will fail in a different way where they cycle like normal but will not open intermittently at certain rpms.

Your options for replacement are to buy new Suzuki Parts House.com which is 10% over cost as if you were an employee or eBay which is always a risk. I have bought 6 or 7 (180-200 each with TBs) from eBay for 2 different bikes and I think all have been good for at least a year or two. I constantly modulate my throttle on the racetrack of aggressive street riding which wears them out quicker. I took one to the Boeing engineer here at work who specializes in electric motors and he said its a cheap/flawed design from Keihin, where the graphite disk wear out quickly.

The SET valve if disconnected will default 100% open based on the retaining spring and will not cause your problem. A SET problem will not open full due to out of spec cable adjustment so your power will be lacking at all times.

If not your STVA then your ECM would be in question but before all use the service manual again and confirm your throttle play is correct then make sure your TPS is in the middle again. TPS's can also wear out. You can see this if you take the TPS off and see the pyramids inside warn down.
 

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If there's no code, it's not the STVA. Period, end of story.

Since your pipe is just a cat back, I wouldn't think it would affect the tune that much. Suzuki claims the EXVA is there for midrange so the fact it's not closing is interesting with this behavior. What's troubling is that your problem is inconsistent. That suggests an electrical issue that is exploited by the vibration harmonic at that RPM. Sounds like it's time to put it on a dyno to try and capture what's going on.
 

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The no code thing is not true. Again; I have replaced 6 of them on 1 bike (2002 750) all of which have produced no codes. The stepper motor is technically still working but at certain points it screws up so what we gather is its not long enough or enough of a voltage disagree for the ecm to send the code (since its technically not failing).

My 2011 GSXR 1000 began to fail similar to new2street where it wouldn't allow the bike to go above a certain rpm one moment but then I would cycle the key and it would be fine. It finally failed riding to work one morning when I gave it full throttle on a straight. The bike would only go up to 89 mph but at least it gave me the C28 code (the motor had completely failed at that point).

Dyno is a good idea so you can replicate the problem while watching all of the servos.
 

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Discussion Starter #19 (Edited)
Thanks for all the input.
PLEASE NOTE: the lack of acceleration around the 4500 RPMs range has only happened a few times.
Mosy the bike just accelerates not at top performance. It does seem to be fine once the engine has been run for a while and is fully warmed up. And after I have done a few quick take-offs. When the engine runs like a true high performance engine it is great, I just can't figure out why that is not all the time. It was when I bought it last summer!
Sorry if I use some incorrect terminology, but since I was not getting a code for faulty exhaust valve (just in front of the cat) or it's motor, should I try hooking it back up? The one thing I did find when I was experimenting with that valve, was that the spring was not hooked on the tabs correctly. It was disconnected. I guess I have no way of knowing if the valve is actually opening fully at highway speeds, but it does appear to cycle through its pre start test properly.
Temps are in the upper 40's here in PA today but the sun is out. I'm willing to hook the valve back up and go for a ride if it's truly better to have the valve closing at lower rpms. Thanks.
 

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If your SET cables are removed then the valve (exhaust) defaults to fully open via the retention spring. Do not plug it back up, just make sure the valve is stuck open either by looking in your exhaust or physically moving the mount open then letting go to see it snap open. Without the cables attached the motor cannot utilize the buttery valve in the exhaust so there is no physical way it can restrict your air flow.
 
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