Thanks to this site I decided to try to rejet my 2001 gs500, and have been trying to get it working right for....a while now.   I started out with main jet that was way too large (140) and promptly saw a major loss of power and overly rich engine. Since then I've been working down the sizes of jets trying to get it right. Right now I'm running the recommended main jet size for a stock setup (135) and still have trouble with it. My max power is at about 3/4 throttle, past that the bike "surges" back and forth like it's bogging down. As I back off the throttle there is a very definite hit in the power at around 3/4 throttle. So I'm thinking about going down to a 132.5 to see if this fixes the issue.

Thing is, I've never heard of anyone running smaller than a 135 main jet on an 01+ gs500. Everything is 135, 137.5, 140s if you're running K&Ns or something like that. Does my particular example of a gs500 just need a smaller main jet then everyone else's? Or is there something else I'm missing? I've checked the float height, replaced all the rubber o-rings and gaskets in the carbs incase there was an airleak, and inspected the boots connecting the airbox to the carbs and the carbs to the engine for cracks/leaks and found nothing.

Other information:
I'm running a 20 pilot and a 60 mid-main with no problems. I'm currently using a hi-flo filtro brand replacement airfilter (same as the OEM) mostly because it was cheaper than buying an OEM suzuki filter.

Extra tidbits:
When I first started I tried running a gsx1400 airfilter to see how that would work (since the wiki mentions it but has no other information on it). I tried a 140 and it was too rich. Tried a 137.5 and it was still too rich (though not as bad). After that I switched to my current filter. The gsx1400 airfilter is larger (taller) than the otherwise identical gs500 filter, but it has a metal sleeve running down the inside of the filter maybe 3/4 of the way, where as the gs500's filter (as well as the hiflo filtro one I'm using) only has a small sleeve running maybe a 1/2 inch to an inch. I'm guessing sleeve is restricting the flow of air through the gsx filter much more than the gs' filter, hence no noticeable power boost from using it (by being able to use bigger jets like you can with a K&N pod or lunchbox or such). Just thought I'ld provide some feedback since the wiki didn't have anything on it.

Hi, do you know which clip your needle is on, or if it is shimmed?

I'm currently finalising between 132.5 and 135 on a stock setup. these sizes are recommended on this forum for stock setups.

132.5 is probably the correct one but I'm still juggling needle position to get it just right and to attack the dreaded 6k RPM flat spot.

QuoteMy max power is at about 3/4 throttle, past that the bike "surges" back and forth like it's bogging down. As I back off the throttle there is a very definite hit in the power at around 3/4 throttle. So I'm thinking about going down to a 132.5 to see if this fixes the issue.

I have this exact issue. Never taken the cars apart and it used to run absolutely fine, but I ended up fitting a wrong air filter a while back, which had a way longer inside sleeve than the stock filter. It caused my bike to run way rich, drowning the spark plugs, and slowly deteriorating to a situation where 120kmph was my top speed. I eventually found the problem and replaced the air filter, as well as the spark plugs. They're all good now and the bik then ran waaaay better again.

However, the problem you describe above, remains. It's only at the end of the throttle now, as opposed to at half throttle, like it was with the other air filter, but it's still there. Everyone's telling me it's got to be my main yet, but I don't have the balls to pull the carbs apart.

I'm really interested to see what you find fixes the problem!

Quote from: MotoSig on August 17, 2018, 01:20:50 PM

Thing is, I've never heard of anyone running smaller than a 135 main jet on an 01+ gs500. Everything is 135, 137.5, 140s if you're running K&Ns or something like that. D

Just about everyone of the 30,000 and counting 132.5 mains I have sold since 2002 would have to disagree with you here.
Stock US bike comes with 130 mains, 17.5 pilots and 60 mids.
For a stock bike, with a paper filter, with stock pipe or slip on or even a full system - as long as the air filter is original in the airbox - you only jet to 20/132.5 and leave the 60's as is. And do 1-2 washers under the needle.
K&N after removal of airbox and slip on/full pipe is 147.5 mains with 65 mids as optional if washers aren't enough.

Cool.Buddha.

Quote from: Sarasibut I don't have the balls to pull the carbs apart.

It's not bad. I was worried the first time I did it but really the most annoying part is pulling off the tank+fuel lines. I've done it so many times now it's almost second nature.   Just keep track of all the tiny screws and it's fine. Thanks for the insight into your issue. 

Quote from: herennowHi, do you know which clip your needle is on, or if it is shimmed? I'm currently finalising between 132.5 and 135 on a stock setup. these sizes are recommended on this forum for stock setups.

The wiki recommends 135, I dont recall seeing anything about 132.5s but I may have skipped over something. At any rate good to know. 

TBH I've never gotten a good/straight answer about needles. All pictures seem to be for pre-01 or dont have pictures to accompany them or are just confusing or all three. I have stock needles so no e-clip positions like the dynojet kits, just one slot to put it in+washers. However I have two different kinds of washers on there and no one has ever explained which is the one I fiddle with or where to actually put them other than "on the needle". Do I need to fit them between the e-clip and the plastic donut? Under the plastic donut? (That's where the thicker one was, the thinner one was above the e-clip.) Additionally the manual refers to the plastic donut as a washer itself. I finally removed the thicker washer that was under the plastic donut but the problem remained. Upon further research on this forum it seems the needle washers only affect mid-throttle not max throttle. So I'll probably stick them back on since mid range was doing fine before.

Quote from: The BuddhaJust about everyone of the 30,000 and counting 132.5 mains I have sold since 2002 would have to disagree with you here.

Ahh. I'ld heard of your kits but didnt know what sizes you actually used in them. Again this is the first I've heard of anyone using 132.5s on a stock setup. But this is good to hear! It means I'm not doing something weird and wacky by getting 132.5s. I'll be ordering some tomorrow and installing them as soon as I can.

Okay so follow up question. From my understanding when setting the pilot air screw, you first properly warm up the bike, then you start with it 1/4 turn out and back it out slowly (1/4 turns or 1/2 turns) until the revs stop increasing. More than 3 turns is too much. I fiddled and fiddled with these and haven't really noticed the revs increasing or decreasing or any discernible difference of any kind between 1/2 turn out and 3 turns out. (Again, after a good 1/2 hour or more of riding to warm it up.) Any insight into this? Additionally (and I think[?] this is a related problem) ever since the rejet I haven't gotten my choke to work right. It is very sensitive and functions almost like a second kill-switch ( ). I can never get the bike to the point where I can turn the choke off all the way, even after it's thoroughly warmed up and no matter the settings on the pilot air screws. I've checked the choke cable and it moves the choke plunger fully in and fully out, so no worries there. I didnt' have this issue before I did the rejet. (notice a trend here?  )

The air screws on the under side in the front part of the carb - no you don't start at 0. You set it to 3 on both and see how it runs as well as do an idle plug check. You set it out or in from there based on those 2. I like it slightly leaner than ideal because that makes it easier to hot start. If it was rich, your hot starts will be harder.
I dunno where you got wiki and 135 for a stock bike.
I have only recommended 135 for a K&N in the airbox with slip on. Stock was always 132.5/20/3 turns 1 washer. You need the stock needles for that setup, and look at the needle, if its got some weird number like 5D0H or something engraved and not have adjustable grooves - that's the original.
Cool.
Buddha.

Quote from: The BuddhaI dunno where you got wiki and 135 for a stock bike.

http://wiki.gstwins.com/index.php?n=Upgrades.Rejetting ->

Quote from: GStwins wikiTo what degree

A conservative Starting Point for upgraded Jetting (Pilots/Mid Main/Main) for a:
Stock GS500 = 20/60/135
Drop in K&N Air Filter Only = 20/62.5/140
K&N Pod or Lunchbox Air Filter Only = 20/65/142.5
Drop in K&N Air Filter + Sports Exhaust = 20/62.5/142.5
K&N Pod or Lunchbox Air Filter + Sports Exhaust = 20/65/145

Additionally the matrices show nothing for a stock gs running a 132.5. Maybe it should be updated to include that then?

Update: Got my 132.5 main jets in, along with more problems.    It bogs alot less on WOT, but it still bogs. There's still not any more power versus 3/4 throttle, now it'll just kinda hold whatever speed I get to with 3/4 throttle once I get up to about 65ish. Additionally it feels like 3/4 throttle has alot less power now I could coax it up (slooowly) to about an indicated 95ish before, now it'll do closer to 85-87 indicated.

Aaaaand, I'm having major fuel issues now. The only thing I changed was from a 135 main jet to a 132.5 main jet, and set my air screws three turns out (they were at 2.5 before). I've double checked my hose routing and such and it's all good with no kinks, but now I can't run on "On" or reserve on the petcock. It'll bog down and die as if I'm running out of fuel, even if I switch to reserve. Just to be on the safe side, I filled up the tank and it still does it. It'll only run on prime. This happens regardless of throttle position. It'll die quick on WOT and take alot longer if I just cruise around 60ish with about 1/4-1/2 throttle, but it'll still eventually run out and die.  I tried setting my airscrew back to 2.5 turns out (where it was before) just incase that affected it any at 1/4 to WOT, and it didnt fix anything. Sounds like bad fuel starvation, I did some more research and it seems that going up jet-sizes can make fuel starvation more prominent.

gstwins.com/gsboard/index.php?topic=13822.msg 117587#117587

Quote from: Hi-TI had a similar issue after rejetting my bike (01).  I noticed the problem had more to do with throttle position-  Ie no matter what gear I was in,  if I went from half to wide open throttle i would stutter and hesitate til I backed it off.

I thought it had to do with jet sizing and needle height and mixture- but in the end I wasn't getting enough gas.

Except I went down a size, so I'm not sure how that would cause this problem to develop.

Only other problem (which might related) is the choke is still super finicky. Still can't get it all the way off and it's very touchy. It stalls out easily and trying to nudge it one direction or the other to keep it from stalling just makes it stall anyways. As it warms up I can coax the choke lever to about 1/2 way off, but I have to leave it there (even when warmed up) to keep it from stalling at idle. I'm assuming this is just because I haven't set the idle air screws properly yet, but I figured I'ld mention it just incase it did have anything to do with my other problems.

Anyways, any insight/help/explanation on the why's and how's would be greatly appreciated. 

If you turn off the tank petcock and thus drain the system, does it run better towards the end? If so, you're not dealing with fuel starvation, but with drowning. I've narrowed my problem down to running way too rich. I think I'm drowning one cilinder at 3/4 throttle, causing the bike to lose speed slowly. If I start at a lower speed and run WOT, the acceleration is less, but still there. If I leave it on prime a bit, it is hard to start. I'm guessing I've got one stuck float needle, or my float height is off. The bike runs significantly better at night, when it's colder, then during the heat of the day. It also runs worse on choke.

I think you have a vacuum leak causing the petcock to not open completely along with other running issues. Insufficient vacuum will cause the slides to not come up and result in the "bogging" you mention. Basically you're never getting on the main jet at all because I bet the needles are staying down. Lots of things you could check but I'm not going to get into it here until you work out the vacuum leak.

You can see what I think about all this on my blog: https://joshkarnes.blogspot.com/2017/09/fixing-common-gs500-carburetor-issues.html

Of course I am talking mostly about the 2-circuit carbs but most of it also applies to the 3-circuit carbs.

Oh and it's not a "pilot AIR screw", it's a pilot NEEDLE and it meters fuel, not air. Knowing that will help logically work out what it's doing. Looser means needle further out of the jet means more fuel. It will really only affect performance at idle and less than about 1/4 throttle up to about 4-5K rpm.

Quote from: SarasiIf you turn off the tank petcock and thus drain the system, does it run better towards the end? If so, you're not dealing with fuel starvation, but with drowning.

I'll try that tomorrow, but considering that it only runs on prime, wouldnt this not be the issue? Seems that if it only gets better by letting the fuel flow more easily (prime) would be opposite of cutting the fuel off and draining it.

Quote from: mr72I think you have a vacuum leak causing the petcock to not open completely along with other running issues.

Are you talking about the bogging regarding WOT whether with my 132.5 main or 135 main? Or the bogging regarding running out of fuel and having to then run on prime? If the latter, then I'm hesitant to think this because I had no problems running it Sunday before I opened it up, swapped the jets for the smaller size, and put it all back on. I've already rebuilt the carbs with fresh o-rings, float needles, etc, prior to this and checked the boots between the airbox/carbs/engine, and double checked all the hoses. Given this, do you still think it's likely to be a vacuum issue?

Additionally, if it is a vacuum issue, I would still see these problems even if I ran a stock 127.5 main right? If so I may try to swap that back in and run it to see how it works. If the problem persists I'll hunt for the vacuum leak and it goes more or less back to stock then I'll conclude it isnt. I hope this doesnt come across as dismissive of your advice, cause it's not.  I'm just trying to work through this problem logically and not chase red herrings.

Also, dont know if I've mentioned it, but I also checked the float height when I first put the 135s in and they where all in spec.

Quote from: MotoSig on August 27, 2018, 04:55:55 PM
Are you talking about the bogging regarding WOT whether with my 132.5 main or 135 main? Or the bogging regarding running out of fuel and having to then run on prime?

Both.

QuoteIf the latter, then I'm hesitant to think this because I had no problems running it Sunday before I opened it up, swapped the jets for the smaller size, and put it all back on. I've already rebuilt the carbs with fresh o-rings, float needles, etc, prior to this and checked the boots between the airbox/carbs/engine, and double checked all the hoses. Given this, do you still think it's likely to be a vacuum issue?

Yes. Could be leaking at the petcock. Cracked hose maybe? could be the diaphragm in the petcock is leaking. Try running it on prime and capping the petcock vacuum fitting at the carb.

There could be other causes. Could be the diaphragm is misaligned (I've done that before). Could be the spring/perch/washer/etc. on top of the needle is misaligned with the spring, could be the needle didn't actually go down into the emulsion tube, sticking needle in the emulsion tube, holes in the emulsion tube clogged, hundred other things. But given the combination of petcock issue PLUS vacuum-leak running behavior makes me think most likely is a vacuum leak.

Replacing all those o-rings was the right thing to do  

Additionally, if it is a vacuum issue, I would still see these problems even if I ran a stock 127.5 main right? If so I may try to swap that back in and run it to see how it works. If the problem persists I'll hunt for the vacuum leak and it goes more or less back to stock then I'll conclude it isnt. I hope this doesnt come across as dismissive of your advice, cause it's not.  I'm just trying to work through this problem logically and not chase red herrings.

Also, dont know if I've mentioned it, but I also checked the float height when I first put the 135s in and they where all in spec.
[/quote]

Quote from: mr72Could be the diaphragm is misaligned (I've done that before).

The diaphragm on the petcock? What do you mean by this? Misaligned how?

Quote from: mr72Could be the spring/perch/washer/etc. on top of the needle is misaligned with the spring, could be the needle didn't actually go down into the emulsion tube,

You're talking about the needle in the carb itself right? If so I'll double check this.

Quote from: mr72Replacing all those o-rings was the right thing to do  

Actually, I think it was on your recommendation several months ago that I did this.

Quote from: MotoSig on August 27, 2018, 05:20:27 PM

Quote from: mr72Could be the diaphragm is misaligned (I've done that before).

The diaphragm on the petcock? What do you mean by this? Misaligned how?

No, talking about the carb diaphragm.

One way or the other, the problem with it running bad at high revs and WOT is most likely because the slide is not coming up. I'd verify that first. Things that can cause that are alignment/etc. issues, vacuum leak, missing vacuum caps, stuck slide guide, etc. The fact that you ALSO have poor fuel delivery when on the vac. petcock points to vacuum leak.

Quote

Quote from: mr72Could be the spring/perch/washer/etc. on top of the needle is misaligned with the spring, could be the needle didn't actually go down into the emulsion tube,

You're talking about the needle in the carb itself right? If so I'll double check this.

Yes. Another cause for the slide to not come up.

Quote from: mr72Replacing all those o-rings was the right thing to do  

Actually, I think it was on your recommendation several months ago that I did this.
[/quote]

Rock on!!

Quote from: mr72/quote]One way or the other, the problem with it running bad at high revs and WOT is most likely because the slide is not coming up. I'd verify that first. Things that can cause that are alignment/etc. issues, vacuum leak, missing vacuum caps, stuck slide guide, etc. The fact that you ALSO have poor fuel delivery when on the vac. petcock points to vacuum leak.

How do I verify this? I can verify it's not stuck by taking the carbs off (again -.- ), reaching in, and moving the slide with my finger. But how do I verify that it moves when under vacuum? I'll double check the caps and such and probably replace the vacuum line from the carb to the petcock.

Quote from: mr72Yes. Another cause for the slide to not come up.

Ok, so is it that it could be misaligned? As best as I can tell it either fits or it doesn't, not sure how it could fit but misaligned... (do you have pictures so I can get a better idea?)

With the tank and airbox off, you can blow into the port where "atmospheric" air enters the diaphragm enclosure with a small length of hose. Its one of the holes on top of the input throat of the carb. You will see it rise. It's hard to say what is "normal" but compare the two and see that they rise and fall smoothly
and in a similar way and that that they stay up with similar pressure applied.

I just wanted to add something that may be overlooked. Remember that the part of the carb that is working at any given point (needle jet, main jet, etc)is based on RPM, not on throttle position. The nature of a CV carb means that you go on the main jet only at high RPM settings - and the carb decides on this due to the vacuum demand by the engine.

I suspect that your behaviour is not caused at all by the main jet as you are probably not at high enough RPM to be using it, based on your description. It's probably a small vacuum leak or there is a problem with the needle/ needle jet operation.

Good luck!

Quote from: MotoSig on August 27, 2018, 05:45:13 PM
How do I verify this? I can verify it's not stuck by taking the carbs off (again -.- ), reaching in, and moving the slide with my finger. But how do I verify that it moves when under vacuum? I'll double check the caps and such and probably replace the vacuum line from the carb to the petcock.

Remove the seat and the airbox. You can see into the throat of the carbs. Run the bike and open the throttle, you know kind of "blip" it enough to get it to rev to 5-6K rpm or so, you should see the slides come up through the throat of the carb and you can watch if they both come up and if they come up together. If they don't come up at all or not until you rev it really high then there is a problem. They should rise and fall essentially together and smoothly.

I forgot to add, this could also be caused by a tear or pinhole in the diaphragm, or if you have gotten carb cleaner on a diaphragm then it can affect the resilience of the diaphragm and the ability of it to move the slides as designed.

Quote

Quote from: mr72Yes. Another cause for the slide to not come up.

Ok, so is it that it could be misaligned? As best as I can tell it either fits or it doesn't, not sure how it could fit but misaligned... (do you have pictures so I can get a better idea?)

Yeah you can get the edge not lined up in the groove, or you can inadvertently wind up with the needle hanging up and not going all the way down, I have done both of these things before. It's not likely, but you know these things can move while you're putting the covers on and you won't know it until you remove the cover again. If the slides are not moving normally when it's running then this is just something to check while you are taking it apart (again).

All this talk really makes me want to go buy a FI bike.

Quote from: mr72 on August 27, 2018, 04:34:24 PM
I think you have a vacuum leak causing the petcock to not open completely along with other running issues. Insufficient vacuum will cause the slides to not come up and result in the "bogging" you mention. Basically you're never getting on the main jet at all because I bet the needles are staying down. Lots of things you could check but I'm not going to get into it here until you work out the vacuum leak.

You can see what I think about all this on my blog: https://joshkarnes.blogspot.com/2017/09/fixing-common-gs500-carburetor-issues.html

Of course I am talking mostly about the 2-circuit carbs but most of it also applies to the 3-circuit carbs.

Oh and it's not a "pilot AIR screw", it's a pilot NEEDLE and it meters fuel, not air. Knowing that will help logically work out what it's doing. Looser means needle further out of the jet means more fuel. It will really only affect performance at idle and less than about 1/4 throttle up to about 4-5K rpm.

I can't tell you how many times I read through that article and how valuable that information was while I was getting my carbs dialed!

Another thing to check would be the screws on the back of the petcock.  Mine were all loose when I had it all apart and checked them on a whim.  Could easily cause both leaking vacuum and malfunctioning petcock.

Quote from: mr72All this talk really makes me want to go buy a FI bike.

Just one more justification to go buy a 790 duke! 

Update: I haven't tried watching the slides rise yet or checked the rest. I bought some a line to replace the vacuum tube between the carb and petcock with (it's a bit smaller ID than the OEM but it'll fit over the nipples) and some vacuum caps and such, along with two new sparkplugs (mostly just preventative). I put in the new sparkplugs and began to take the tank off to begin checking everything when I noticed the vacuum tube between the carb and petcock had a major kink in it! So much for "double checking" everything! I missed it when going everything last time, as the kink was tucked up between the frame and airbox where it was hard to see. I straightened this out, screwed the tank back on and fired it up. BAM! No more bogging down on "on" or "reserve"! Running WOT behaves better too. Now I feel like a bit of an idiot. 

It still surges slightly on WOT, but it's alot less noticeable than when I was running on a 135, my 132.5 now, or any of my previous main jets (140 and 137.5). It only noticeably surges at 8K rpm and above (which is an improvement! It used to bog at most any RPM above 3-4K with WOT), mid throttle still seems weaker than it did before, but still stronger or as strong as full throttle. WOT will only reach about 8L to 8.5K rpm in 6th gear (with a +5 tooth rear sprocket), where as with 3/4 throttle I can still coax it faster than that. It is marginally faster WOT than it was before, however.

I ran it WOT down a few miles, turned around, ran it WOT most of the way back (after I got around the semi), for was a good mile and a half atleast. Hit the kill switch and coasted in to the driveway. Then I checked the plugs and got pictures to throw up on here:

Left cylinder (as you sit on the bike):






Right cylinder:





If I understand correctly, the white means they're both running a little lean? Or is that a "healthy" plug color?

That's not a bad color for a plug, a hair lean - and you should be able to get there with needle or air screw or float level - so what else is it doing - how is it 1/2 throttle and 1/4 and 1/8th ...
Cool.
Buddha.

I wouldn't read too much into the plug color but it does look a little like the left cylinder might be lean.

Check and be sure the slides are coming up. IMHO. Left side may not be, which would make it quite lean at WOT. Or other things (needle stuck in wrong place, assembly error, bad vacuum leak on that side, etc.). But most of the things wrong, first sign will be the slide is not coming up. If the slides are coming up in concert and going down in concert you can basically rule out most vacuum issues. You could still have a vacuum leak at the intake boot o-ring causing it to suck air in at high vacuum when the slides are all the way up and lean it out (WOT/high-revs).

But if it's running well and your plugs are in the ball park (and they are), I'd leave it alone until next time I had to take it apart for any other reason, then check all that.