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I just bought my first bike! Really excited about my new 2001 GS500... except... it's having some issues that I'm having a hard time diagnosing! Hope I didn't get TAKEN on the sale

I bought the bike knowing that it had some carb issues, and got the guy to knock $200 off the price for a carb clean. Which, of course, I'm going to try to do myself before I take it to someone. I have a lot of air-cooled auto engine experience. Never been great with carbs though. Haven't gotten to it yet, but I'm worried it's not a simple carb problem... Sorry, this is going to be lengthy!

Here's what's happening:

when the bike is cold- (particularly when the weather is cold)
difficult time starting
under 1/3 choke applied = under 1k rpm idle, dies (seems like the choke is REALLY sensitive. On or off.)
over 1/3 choke applied = 5k rpm idle
blip throttle, bike dies
gradual throttle bike sputters and jerks, then revvs up to 3k

If I really fiddle with the throttle I can find a tiny sweet spot where it sits at 2500rpm until it warms up a bit. Then it still sputters and jerks and dies a few times as I pull away from the first few stop signs. Then I have to revv it pretty good for a few stop signs but I don't like putting a cold bike up to 6-7000 rpm just to warm it up quickly! Especially to a bike that I'm pretty sure is due for a valve adjust...

when the bike is hot-
rolling off the throttle to shift, rpm blips on its own(6k)
coming to a stop, rpm hangs around 3k, 4k
let the clutch out just enough to pull the rpm down below 3k, and idle drops to 1200, then idles nicely @ 1200-1500
makes power from 5k rpm+, otherwise lugs pulling away from a stop
Also sounds a bit like there's pinging in the exhaust, ticking sound from the front of the motor when I roll off the throttle at high-ish rpm

I already tried pulling the tank and checking for vacuum leaks. I sprayed all around the boots that I could find with WD40 while the bike was running to no result. I checked the cables, including the choke and none of them seem to be sticking or binding. Everything is snapping back into place like it seems like it should. I also ran the better part of a pint of seafoam through it (mixed in the gas) and it seems to have gotten it to idle fine when it's hot as I described above as a result. Next weekend I'm planning to pull the carbs and clean them (after my Clymers manual comes in the mail). Any theories as to what's going on here? I'd pin it on the mixture or the idle set screw except that it idles nicely after it's hot (provided I pull the the rpm down with the clutch at every stop)

I think my plan for now is to pull the carbs and have a look, then give it over to a mechanic. Any ideas? Should I play with the mixture? or the idle speed screw?

I also can't seem to find a carb rebuild kit for an '01 GS500 so if anyone has a lead please let me know, otherwise I'm going to be re-using the rubber!

Thanks in advance!

It sorta sounds a typical jetted-lean-from-factory Japanese bike to be honest.


The factory jets them lean to help meet emissions and that makes them cold blooded.

There isn't really a 'rebuild kit' for most motorcycle carbs, just jets and other individual parts. Your carbs probably have plugs covering the idle/air screws (but I'm guessing) to prevent tampering, hopefully your Chilton manual will show you how to drill out and adjust them.

Yeah I'd heard that they were jetted lean, but idling at 5000 rpm? That's more than a lean jet from the factory...

Add about 2oz of Seafoam to a tank of gas.

I ran 10oz of seafoam through the gas. Didn't help!

Sorry, didn't mean to give the impression that the carb was working correctly. But a miss-adjusted idle, or idle circuit in a factory lean carb can cause high idle problems. You may find that your manual will give you info on how to adjust that out, or how to clean the low speed jetting to fix it.

It is not uncommon for people, like the P.O., to try to adjust the cold-blooded leanness out by messing with the idle and/or throttle cable slack, with the results your bike is showing.

Your choke is probably working fine, on or off, no in between. In fact, I would guess it's not really a choke, but an enrichment circuit that just adds more fuel to the intake air (but that guessing again, no matter, the result is the same). If it was a vacuum leak, it would not only idle high, but probably surge a fair bit too, so that is unlikely, but not impossible.

Thanks for clarifying! Yeah, I'm beginning to think it's just poorly tuned / a bit dirty. As I'm running through my tank of gas with the seafoam in it seems like it's getting a bit better. Still odious when it's cold though. I blip the throttle at a stop sign and it stumbles, dies. Really not doing wonders for my confidence riding to work in SF traffic...

I'm still going to pull the carbs off it as soon as I get a chance and I'm going to give it a thorough once-over checked against the clymers I have on the way, check the valve lash and try to balance the carbs. At that point I'm not sure what else it could be... hopefully that'll take care of it?

Any suggestions on how to set your mixture? I've heard the WD40 method where you spray in the intake and it stumbles if it's rich or revvs if it's lean. And I've also heard the screw it in until it stumbles, screw it out until it stumbles and then set it for the middle...

Johnj wrote:Add about 2oz of Seafoam to a tank of gas.

Pour in the whole can!!!!!!---Buzz

check for vacuum leaks too. Behavior like you described is typical of a vacuum leak issue.

Yep, definitely clean your carbs and while you're in there check your vacuum lines. As for the valve adjust, that bike shouldn't need it til 15K or so... Not sure how many miles are on it.
Wrider