Rejetting '02 GS500

[1990dtgl98]

Hey guys!

Bought a 2002 GS500 for the wife. Has 12k on it. I just replaced the tires and chain sprocket. However she only drove it 3 times last year. She's hesitant to ride it becuase it shudders and stumbles at idle and partial low RPM throttle. I thought it was just bad gas/gummed carbs, but pulling everything apart and cleaning it didn't solve the issues.

Reading up it seems that the problem could be related to it running lean. It does backfire out the intake slightly when the throttle is held open at say 10% (usually on a car that means lean if it's backfiring out the intake).

I was wondering if this could solve the problem. She loves to ride and I hate to see it sit because she doesn't trust the bike (doesn't help she dropped it after it stalled starting out at a stop sign). Anything to fix the problem would help!

If it is, what kit is recommened? Is it better to peice the parts together (buying the needles/jets/washers seperate)? Or would a dynojet or similar kit work?

If it's better to piece...get jets, needles, washers, or just jets/washers? I'm reading the stickies and wiki posts...but anything for a '02 in particular? I hear different things about slides, air mix screws, etc.

I'm proficient with cars, I'm kinda hoping these will be the same as a car carb. 

[RossLH]

Is it stock, or are there any intake or exhaust modifications? If not, rejetting is not necessary. Try synchronizing the carbs.

[gsJack]

My 02 GS with stock intake and exhaust has run 98k smooth happy reliable miles with the jets untouched.  Haven't even removed the caps over the idle mix screws.  Untouched 02 GS carbs are happy GS carbs.   

[codajastal]

My 02 GS with stock intake and exhaust has run 98k smooth happy reliable miles with the jets untouched.  Haven't even removed the caps over the idle mix screws.  Untouched 02 GS carbs are happy GS carbs.   

I agree wholeheartedly

[1990dtgl98]

If it's not the fact they run super lean... What could be causing the low rpm stumble and studder as well as the slight backfire through the intake?

[gsJack]

.................it shudders and stumbles at idle and partial low RPM throttle. I thought it was just bad gas/gummed carbs, but pulling everything apart and cleaning it didn't solve the issues...................

When you use the word shudder I think of a GS running on 1 cyl with the other coming and going.  With it stumbling at idle pull a plug wire and if it doesn't die put it back on the plug and pull the other one.  If it dies it could be a plug wire loose in the coil, a bad ignition pick-up, or a carb problem other than jets. 

The plug wires screw into the coils and are then bonded in tight.  You can't turn the wires in the coil by grabbing them and twisting them hard if they are OK, if you can turn them they are not.  One of the common causes of a GS running on one cylinder.  If you checked for spark in the conventional manner that just proves the circuits are making and breaking to produce spark but doesn't prove they are still sparking under pressure in a running cylinder.

Have you ever checked valve clearances, you don't mention them.  Do you have cold compression on both cyls?  I'd be satisfied with a thumb over the hole and crank check for now if you don't have a gage handy.  If one doesn't pop the valves need attention.  If they both pop cold then valves aren't causing your current problem.

[1990dtgl98]

.................it shudders and stumbles at idle and partial low RPM throttle. I thought it was just bad gas/gummed carbs, but pulling everything apart and cleaning it didn't solve the issues...................

When you use the word shudder I think of a GS running on 1 cyl with the other coming and going.  With it stumbling at idle pull a plug wire and if it doesn't die put it back on the plug and pull the other one.  If it dies it could be a plug wire loose in the coil, a bad ignition pick-up, or a carb problem other than jets. 

The plug wires screw into the coils and are then bonded in tight.  You can't turn the wires in the coil by grabbing them and twisting them hard if they are OK, if you can turn them they are not.  One of the common causes of a GS running on one cylinder.  If you checked for spark in the conventional manner that just proves the circuits are making and breaking to produce spark but doesn't prove they are still sparking under pressure in a running cylinder.

Have you ever checked valve clearances, you don't mention them.  Do you have cold compression on both cyls?  I'd be satisfied with a thumb over the hole and crank check for now if you don't have a gage handy.  If one doesn't pop the valves need attention.  If they both pop cold then valves aren't causing your current problem.

When I say stumble I mean at partial open throttle (around 10 percent). It idles fine and doesn't really have any studder unless your on the throttle slightly.

It also hesitates to rev when you quick blip the throttle. It will rev fine if your gradually grt on the throttle,  but a quick full throttle blip and it will stumble/studder.

[gsJack]

When I say stumble I mean at partial open throttle (around 10 percent). It idles fine and doesn't really have any studder unless your on the throttle slightly.

It also hesitates to rev when you quick blip the throttle. It will rev fine if your gradually grt on the throttle,  but a quick full throttle blip and it will stumble/studder.

Your 1st post said "She's hesitant to ride it because it shudders and stumbles at idle" and the word shudder (to tremble convulsively) mislead me a bit but now since it idles fine but stumbles a bit off idle and won't take quick throttle blips I'm wondering if your referring to a cold/partially warmed engine or if you mean on a fully warmed engine?  And how are you using the choke?

There are many complaints here about the GS being cold blooded and needing a long warm-up before riding off but I don't find it a problem with 01 and later GSs with the 3 circuit carbs.  Riding year around here in NE OH I go into the garage, start the bike on choke (full winter/half summer), go over to the bench and put on helmet and gloves and return to the bike and get on, set the choke for takeoff, and can then hit the street using as much and as quick a throttle as I want to without balking.  I can close the choke as soon as I hit the street on warmer days but wait till I get past the traffic light down the block to close it on colder days.

Setting the choke for takeoff means adjusting the choke closed only to the point where I can still quick blip the throttle repeatedly without balking.  So I've quick blipped my 02 GS engine repeatedly all the way to 98k miles and counting.

Saw your post yesterday but was hoping one of our I wanna rejet it guys would hop in and give you jet size info for your 02.  Might as well give it a try if you want to.  By the way, did your wife have similar cold bike problems on the carbureted Rebel she rode previously?

[1990dtgl98]

When I say stumble I mean at partial open throttle (around 10 percent). It idles fine and doesn't really have any studder unless your on the throttle slightly.

It also hesitates to rev when you quick blip the throttle. It will rev fine if your gradually grt on the throttle,  but a quick full throttle blip and it will stumble/studder.

Your 1st post said "She's hesitant to ride it because it shudders and stumbles at idle" and the word shudder (to tremble convulsively) mislead me a bit but now since it idles fine but stumbles a bit off idle and won't take quick throttle blips I'm wondering if your referring to a cold/partially warmed engine or if you mean on a fully warmed engine?  And how are you using the choke?

There are many complaints here about the GS being cold blooded and needing a long warm-up before riding off but I don't find it a problem with 01 and later GSs with the 3 circuit carbs.  Riding year around here in NE OH I go into the garage, start the bike on choke (full winter/half summer), go over to the bench and put on helmet and gloves and return to the bike and get on, set the choke for takeoff, and can then hit the street using as much and as quick a throttle as I want to without balking.  I can close the choke as soon as I hit the street on warmer days but wait till I get past the traffic light down the block to close it on colder days.

Setting the choke for takeoff means adjusting the choke closed only to the point where I can still quick blip the throttle repeatedly without balking.  So I've quick blipped my 02 GS engine repeatedly all the way to 98k miles and counting.

Saw your post yesterday but was hoping one of our I wanna rejet it guys would hop in and give you jet size info for your 02.  Might as well give it a try if you want to.  By the way, did your wife have similar cold bike problems on the carbureted Rebel she rode previously?

Throttle blip issue and partial throttle stump happens at any time. Does it cold or after riding for 45 min in July.

No real issues with the rebel besides some issues with a high rpm misfire. Didn't realize I said she had a rebel earlier lol

[gsJack]

You didn't mention the Rebel, Mr Google told me. 

There's a lot of rejetting info on the wiki, maybe you've already seen it.  Can't vouch for it's accuracy myself but it came from fellow board members.

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

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