Losing Power in higher gears at 5000-6000 RPM

[Kijona]

Has someone (previous owner) gone messing with the mixture screws? It might help to remove those and make sure that one of the tips hasn't broken off. Someone will need to help me out with the exact factory setting, but I believe it's 3.5 turns from closed.

Have you ruled out ignition issues? I had a bike that acted similarly - turns out that it was a fault in the spark plug boot allowing it to arc at higher RPM.

[smokestack]

Methinks slippy clutch.

[Big Rich]

From the original post:

Initially, I thought that this was the clutch slipping, but the more I ride, and the more I think about it, I'm not seeing an RPM spike when this happens...
(End quote)

So it's not looking like a slipping clutch guys.

[rscottlow]

Methinks slippy clutch.

Yep...that was my original thought too. It's worsened considerably, as I've pulled out the carbs, made adjustments, and reassembled. So that makes me think it has to be related to the fuel mixture. I checked the float heights again - one was off a little bit, probably from me fiddling with it so many times. I readjusted it to 13mm, and now it's bogging down all over the place. I've tried messing with the choke while riding - that doesn't seem to have much of an effect.

So...originally, it was only bogging down during hard acceleration in higher gears. I adjusted the floats, but did not reconnect all of the vacuum hoses correctly. Since it didn't seem to be running right, I adjusted the idle screw and was able to ride home. Next, when I took the tank back off to fix the vacuum hoses, I also cleaned the jets - they seemed clean already, but I thought it wouldn't hurt to soak them in carb cleaner. Upon reassembly (and the vacuum hoses being hooked up correctly), it started bogging down in lower gears at high RPM as well. I readjusted the idle screw. Took the carbs apart once more, and did my most recent float height adjustment, and now it's bogging down everywhere. So I'm back to square one, but it's currently worse than it has been since I started. Since it got worse after working on it, I feel like it has to be something that I did wrong, but at this point, I'm clueless as to what that might be. That's why I keep going back to float height...that's pretty much the only thing I've touched...

[rscottlow]

Has someone (previous owner) gone messing with the mixture screws? It might help to remove those and make sure that one of the tips hasn't broken off. Someone will need to help me out with the exact factory setting, but I believe it's 3.5 turns from closed.

Have you ruled out ignition issues? I had a bike that acted similarly - turns out that it was a fault in the spark plug boot allowing it to arc at higher RPM.

I don't know much about what the PO did with this bike. I know it had been down prior to my purchase (PO claimed it happened before he bought it). It's got aftermarket mirrors, signals, passenger pegs, and bar ends (all an obvious result of being dropped). The signals were never wired correctly, so whoever did the replacement clearly did not know what they were doing with it. I bought the bike very early this spring (late Feb, early March), and it had been properly winterized by the PO or his mechanic. After I bought it, I had an issue where the bike was not fueling properly - it turned out to be a leak in one of the carb floats, which I replaced. I also ended up replacing the signal generator after the bike mysteriously stopped getting a spark. Since then, I had no issues with it until I started riding harder and noticed it bogging down in higher gears.

I'll check on the mixture screws - it's possible that the PO could have messed with them to compensate for the one float not floating due to the leak? And after I replaced the float, I guess that could have caused the issue to become more apparent. When I originally put the new float in, I think I forgot to adjust the float height. So then, when I corrected the float height, that could have caused the issue to worsen and become noticeable in lower gears? - So I guess my next question is, where are the mixture screws? (I have a manual at home, so I can look later...).

I have not yet ruled out any ignition issues - everything thus far has pointed towards fueling, so that's all I've investigated yet.

[The Buddha]

That dropping rpm with increasing load - 10k in first, 8k in 2nd, 6k in 3rd, 4k in 4th etc etc - are likely the result of a diaphragm with a tiny rip.

You could also have a plain jetting issue.

Definitely not slipping clutch, with a slipping clutch you rev out like you're in neutral, but not get any faster. You'd in fact get slower with increasing revs.
If you're doing 40 @ 4k and you clutch is slipping, usually it will slip on acceleration, you'd be doing 6k but be only going 30 in the same gear.

Cool.
Buddha.

[rscottlow]

That dropping rpm with increasing load - 10k in first, 8k in 2nd, 6k in 3rd, 4k in 4th etc etc - are likely the result of a diaphragm with a tiny rip.

You could also have a plain jetting issue.

Definitely not slipping clutch, with a slipping clutch you rev out like you're in neutral, but not get any faster. You'd in fact get slower with increasing revs.
If you're doing 40 @ 4k and you clutch is slipping, usually it will slip on acceleration, you'd be doing 6k but be only going 30 in the same gear.

Cool.
Buddha.

Your sentiment about the clutch makes total sense to me - I jumped to that conclusion when the problem started, but after I rode a couple more times I realized that couldn't be the case.

Jets are all stock sizes - I pulled them out and soaked them in carb cleaner for a couple of hours, then sprayed some carb cleaner through them just to make sure they were clean.

Where is the diaphragm located? I haven't taken the tops of the carbs apart at all - I don't have the tools or the know-how to re-sync the carbs, so I've avoided messing with anything that I'm afraid could do more harm than good...

The problem worsened after disassembly and reassembly, and even after checking several times, I'm sure that all has been put back together as it should - so perhaps this is the wrong assumption, but I feel like something I did made the problem worse. I just don't know what it could be.

[FreakyFonz]

Bumping to be able to find this thread again.

I just bought my GS500E '08 last week and I'm having the exact same problem of not gaining extra power at 6K+ RPM.
Although for me it's like this in every gear, time to learn how to clean carbs..

[HPP8140]

Diaphragm is at the top. Just remove 2 screws to remove black cap.

[rscottlow]

Diaphragm is at the top. Just remove 2 screws to remove black cap.

Thanks, sounds like it'll be easy to check this one out...I'll hopefully be able to report back this evening.

[The Buddha]

Misassembly of the diaphragm can cause this too. And the diaphragm getting a little damage from a bad assembly job also is possible.
Cool.
Buddha.

[rscottlow]

Misassembly of the diaphragm can cause this too. And the diaphragm getting a little damage from a bad assembly job also is possible.
Cool.
Buddha.

I'll look into it...I haven't had the top of the carbs apart yet, so if this is the case, it would have to have been done prior to me purchasing the bike 6 months ago. I suppose it's possible that the PO made adjustments to compensate for the bike running poorly, so in correcting the float height adjustments to spec, the problem is getting worse for me?

[rscottlow]

I think I may have found the problem (thanks Buddha!). I finally got around to checking the diaphragm, and this is what I found. I haven't checked the other side yet (my wife is out shopping this morning, and I have the kids), but I was too excited when I found this, not to share right away. Once my wife gets home, I'll get this thing out for a test ride, and hopefully be good to go.


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[rscottlow]

Update: took a closer look, and whoever installed it had it pinched under the cover. I won't be able to get it seated properly, so I'm going to order a replacement. Any suggestions? Partzilla? Or is there a better/cheaper option?


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[rscottlow]

Another update: I managed to get the existing diaphragm seated on there properly. There are still creases where it was punched under the cover, but I looked pretty closely and didn't see any tears or holes. I've got it all back together...just waiting for my wife to get home so I can test it out. It should at least be running better than it was.


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[rscottlow]

And...one more update for today. Got out for a quick test ride. It's much improved, but still running overall sluggishly. It takes off slow in first, and if I'm taking off on an incline, it has a lot of difficulty getting up the hill. Once I hit 5500, power improves significantly. I can go through the gears keeping it at higher RPMs and it rides okay. Just slower than it should. Am I to assume that since its creased on the edge, the diaphragm is not sealing? I'm on the verge of ordering a replacement, I was just hoping to be able to ride until it arrives.


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[mr72]

This is sort of the opposite of the problem you had before, no? Now it runs fine at >5k rpm but is iffy at lower revs?

I am far from an expert (just read my other rambling posts trying to get my bike to basically run right) but it still sounds to me like maybe it's running lean on pilot. Maybe you just need to adjust the idle mix needles a bit and it will improve. You might try riding it with a little bit of choke on and see if the lower rpm hesitation or lack of power improves at the low revs. If so that might point to a lean idle/pilot mixture.

[W201028]

Did you check out the fuel flow to the carbs? If the flow from the tank is restricted (most likely a clogged petcock or two) then you will not have sufficient fuel flow to the carb bowls. The bike might run and idle and rev up fine for the first few minutes, but then starve for fuel after a short ride.

Ive ridden many machines around my property, only to discover that the petcock was turned off the whole time. You would be surprised how far a bike will go on the bowl alone.

However, I have to add my standard question; when was the last time you checked the valves?

[rscottlow]

This is sort of the opposite of the problem you had before, no? Now it runs fine at >5k rpm but is iffy at lower revs?

I am far from an expert (just read my other rambling posts trying to get my bike to basically run right) but it still sounds to me like maybe it's running lean on pilot. Maybe you just need to adjust the idle mix needles a bit and it will improve. You might try riding it with a little bit of choke on and see if the lower rpm hesitation or lack of power improves at the low revs. If so that might point to a lean idle/pilot mixture.

Haha, I hear you. I've been following your progress with much empathy. Yeah, it basically is the opposite of what it was doing before. I'll see how it runs with the choke on tomorrow hopefully. Then I'll check the idle screws and probably reset them to spec and see what happens.


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[rscottlow]

Did you check out the fuel flow to the carbs? If the flow from the tank is restricted (most likely a clogged petcock or two) then you will not have sufficient fuel flow to the carb bowls. The bike might run and idle and rev up fine for the first few minutes, but then starve for fuel after a short ride.

Ive ridden many machines around my property, only to discover that the petcock was turned off the whole time. You would be surprised how far a bike will go on the bowl alone.

However, I have to add my standard question; when was the last time you checked the valves?

I haven't checked the valves. Until this point the bike appeared very well maintained. The PO said he was told the valve stem seals were bad, but I don't know how much that would affect how it runs. This is my first bike, and I just got it in the spring.

I can look into fuel supply if the idle adjustment makes a difference. I'm also still considering that the diaphragm may be leaking air, but I don't know if the way it's running now supports that hypothesis.


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