anxious idle

[Chris_B]

hello,
My bike, a 99 GS500 doesnt seem to be running quite right, it will idle well and rev well until it warms up. Once its warm when you give it gas it likes to stick around 4-5k rpm until eventually 20 seconds or so, it calms back down. Im wondering what would cause this? my mixture screws are set at 2 and a half turns out. It has a K&N uni-filter and an exhaust system. Im thinking vacuum leak, I cleaned the chokes and the o-rings on the mixture screws look ok. the carbs were cleaned very well. Why is this happening?
Thanks
Chris

[Chris_B]

Is there anybody out there?

[Toledo Jim]

I had that also, adjusted the idle when engine was warm and it was doing this, had to play with idle a couple of times to get at about 1300 rpm (when warm, not cold) but that solved the problem for me. :dunno:

[Chris_B]

interesting. Mine will still idle nicely when its warm, and you can rev it to around 2000-2500 rpm without the rpm's going insane high, but anywhere after 2500 and it just takes off and does not like to settle down, the idle is not a problem at all. Im thinking mabye the needle jet needs to be adjusted, a lean mixture will do this, right?

[Toledo Jim]

That is exactly what mine did, and all it took to fix it was playing with the idle when warm.
ymmv

[scratch]

interesting. Mine will still idle nicely when its warm, and you can rev it to around 2000-2500 rpm without the rpm's going insane high, but anywhere after 2500 and it just takes off and does not like to settle down, the idle is not a problem at all. Im thinking mabye the needle jet needs to be adjusted, a lean mixture will do this, right?

You mentined in your first post that you have an aftermarket exhaust, and all you have done is adjust the mix screws, and install a UNI-filter. Without jetting for the pipe you are still lean. Installing 40 pilot jets will help, and you are correct about shimming up the needle (changing the needle jet should not be neccessary). Also, since you will have the floatbowls off the carbs (and the carbs off the bike), you might as well as change out the main jets. I don't know what kind of exhaust you have, but you can find the proper jetting for your particular setup in the FAQ.

[Chris_B]

The exhaust is a home made contraption that came with the bike. The problem im having is that I got the bike with the top end of the engine taken apart and I dont know if the person before me changed the jetting. I have a feeling not because when they tried to put the motor back together they bent every valve and I had to get a new head for it.

[rritterson]

your idle adjust screw is off. Just turn it until it idles properly.

[ratz]

I have had this problem as well. I disassembled the carbs for a thurough cleaning, right down to the pilot jet (it was curroded shut). Once the pilot jet, and emulsion tube was cleaned, the bike ran  better but at high idle.
Adjusting the idle screw, only helped bring the idle down, now I have the same problem as you, when I rev it, it seems to hang up.
No matter how I fine tune the Idle, it is not having any effect on the rpm's hanging up after I rev it...

[mjm]

I have had this problem as well. I disassembled the carbs for a thurough cleaning, right down to the pilot jet (it was curroded shut). Once the pilot jet, and emulsion tube was cleaned, the bike ran  better but at high idle.
Adjusting the idle screw, only helped bring the idle down, now I have the same problem as you, when I rev it, it seems to hang up.
No matter how I fine tune the Idle, it is not having any effect on the rpm's hanging up after I rev it...

Causes of hanging idle include:

Too Lean - might need re-jet, might need carbs cleaned, might have an intake leak.
Valves need adjustment - several people have driven themselves nuts trying to fix carbs where it was valves causing the problem.