Recently had my 2004 GS500F with ~15k miles serviced. Carbs were cleaned and balanced, and valves were adjusted to spec. So, the issue is that my bike basically doesn't really like running at WOT. 60-70% throttle or so feels great, but when I go to WOT there's just general hesitation and shaky power delivery compared to 60-70% throttle. It's super annoying because I've pored over forums about this but can't seem to find a culprit. Shop where I had it serviced also confirmed that jets are stock. I already took it back to the shop weeks ago and they leaned up the fuel mix a bit, which helped a bit I think. Shop owner said that he spoke with Suzuki techs and took fuel mix screw to 3.5 turns or something along those lines. Anyhow, any suggestions? Don't want to have to resort to getting used to not being able to twist the throttle all the way...

Seems like WOT issues would have to be a problem with the main jets or fuel delivery.

Are your carbs, exhaust, air box, and air filter all stock?

I'm guessing float level is off or a clogged main jet.
Mixture screw shouldn't effect WOT (its for idle and off idle mixture) and 3.5 turns is too far out anyways. What does "leaned up the fuel mix a bit," mean exactly?

So esentially you are asking, what did the dealer break, you asked him and he told you not his problem?

Good info bluesmudge.

One thing, I think high float level would affect the bike across the range,not so?

MD13, what country are you in? Main jets varied by country.

this bike has had 14 years for people to say "more gas = more power". Ill bet your main jets are NOT stock, AND that your needle is shimmed.

Id first check all vacum seals are present (like on the balancing ports)
check vacum hose to petcock is in good condition
Check tank breather is clear
check float levels with clear tube and
then check main jets.
All that should take you one evening and very few tools, except for the main jet. it can be done in an hour IF you have changed out the float bowl screws for allen head bolts. However if the tech. has been in their recently you should be able to get in with one of these. But be carefull those are JIS screws. Might be easier to remove carbs first time and replace the screws when you check the main jet.  (as I doubt the tech. has really been in there)

Yes everything is stock to my knowledge. I bought it used and it came with an aftermarket yoshi exhaust though so I swapped that with a stock one. To be clear, it was serviced by a small local shop and dealing with them was an absolute nightmare, quality of service was really bad. And yes I tried to bring it back to them to fix the issue and adjusting the air fuel mix was the best they could do. I'm pretty new to dealing with my bike mechanically so doubt that timeline is accurate but should give it a shot over the rainy week... I'm in CA by the way. Yeah after reading a bunch I guessed it was a jetting issue but that's why I had them check that the jets were stock.

Was it the "slip on" Yoshi that looks relatively modern and attaches to the stock headers or the old school full system Yoshi?
The original Yosh pipe for the GS500 was a full-on race pipe like the Vance & Hines. Very loud and flows a ton of volume. I doubt anyone would throw that on there without a re-ject.

Did the bike run differently at WOT when you swapped the pipes?

Did the shop tell you the jet sizes so that we can confirm they are stock?

herennow, I think if the float levels were a little low the bike would be starved for fuel at WOT. If too high then yeah I think it would affect the full range.

This is why I don't like shops. They say they adjusted the valves. Did they tell what the clearances were before and after and what shims were installed before and after? They say the carbs have stock jets but how do we know that they know what the stock jet sizes are.

3.5 turns out is too much, and indicates you need to jet up the pilot jet.

of course that won't affect WOT. WOT is going to be the main jet, but in your case I'd say either the slides are sticking, diaphragms damaged, severe vacuum leak or very low float level. Or all of the above.

Yeah slip on carbon yoshi. Was really loud and had a hold in it from going down so I replaced it. Embarrassingly, it's hard to say if the bike ran different after I put the stock pipe on. I know I was always really underwhelmed with the performance but didn't put many miles on with the yoshi pipe to compare. Yeah shop didn't give me any details. Based on the ideas presented in this thread, how much should I expect to spend for a dealer to figure it out? Really close to just getting rid of the thing, even though I'm ok with the power otherwise but it has just been such a headache. Spent a lot of money at the shop unfortunately and just couldn't keep going back to them to make it right because it was so clear that they couldn't figure it out.

You need to work in it yourself. A cheap old motorcycle like this is false economy if you have to pay for minor work like carb cleaning and vacuum leak diagnosis.

3 options:
1.) Find a good, honest, motorcycle mechanic that actually works on carburated bikes. They should be able to get it working right for around $500. Dont go to a dealer service department.

2.) Learn to work on it yourself. A GS500 is a great bike to learn how fun motorcycle wrenching can be. A service manual, some basic research on how carbs work, and a few basic tools is all you need. Dont expect to get it right the first time, expect to learn and eventually feel proud of what you have accomplished.

3.) Sell it and cut your losses.

^^^^

No B.S. from Blue Smudge.

Thanks, I'm between 2 and 3... will probably attempt 2 if no luck with 3 

Will be changing out spark plugs this weekend and looking for vacuum leak inspection resources for the GS in the meantime.

Try this first:

https://joshkarnes.blogspot.com/2017/09/fixing-common-gs500-carburetor-issues.html

Erm. I have an update which hopefully should help... something. So it won't start with the choke anymore by the way. I have to start it only without choke.


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Then it's probably way too rich at idle.

Would that affect WOT though?


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There is probably more than one thing wrong. You may be over diagnosing it. Just do what my blog post said and fix everything at once.

Have done a lot of reading and a bit confused how to change fuel mix at idle. Isn't this sealed off in the US? If so, how did my mechanic adjust them? Apologies if these are dumb questions, folks.


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there is a little cap over the screw you drill a small shallow hole into the cover and pull it out by inserting a strong wire or something like that. Google should give up some examples.

The caps are probably already drilled out. Either by the previous owner or by the shop when they adjusted the idle fuel mixture.
On brand new carbs you see a brass cap where the mixture screw should be. You will see the head of the brass mixture screw. Unless the shop was lying.

You adjust fuel delivery at idle with the mixture screw and the pilot jet. Other things that could the bike at idle, like floats, are set it stone or have factory specs that shouldn't be messed with.
When there are problems with a bike thats been monkeyed with and you don't have much experience with that bike its best to do as mr72 is saying and just do a full clean/rebuild of the carb back to stock specifications and test with the stock exhaust and air filter. I just fixed up a bike that had been sitting for 10 years using this method.

I've been struggling with the WOT crap on my 95 as well. With the 01-02 carbs it was dismal. I went back to the pre 00 carbs and its a lot better.
My basic thought of late with the other issues its having - like losing 1 cyl at idle and smoking a very wet gassy smoke at low rpm etc - I'm leaning towards a leak in the petcock diaphragm, leaking fuel into the vacuum side. Mine also acts like its starving for fuel, as well as act rich at other times.
Cap off the vacuum line and the petcock and run the thing in prime. If it runs fine, its a leak in the petcock vacuum diaphragm.
Cool.
Buddha.