erratic idle problem?

any advice on an erratic idle on a '95 XR600R? one time it idles normal, chop the throttle and it floats slowly down to normal, next time it idles high.

ive already made sure the throttle is not sticking. also the air screw dosent have much bearing on the problem. if i turn it all the way in till it seats closed the bike still runs, higher rpm as it gets closed. it will stall after several seconds or after i rev it up a few times when the screw is seated though.

im sure youd like to know the jetting but ill have to look it up tomorrow. bike runs good otherwise, no surging or poping, good power etc. just goofy idle. i have replaced the o-ring for the air screw also but no difference.

thanks

jason

Have you taken the carb apart and cleaned it out real good? Perhaps there's a bunch of varnish, gum or goo inside the carb that just needs to be cleaned out. WD40 usually does a good job of cleaning the inside of a carb (jets, passages, float pin, float bowl, etc). Hopefully you'll find something obvious once you take your carb apart.

Originally posted by Jason Pettis:

any advice on an erratic idle on a '95 XR600R? one time it idles normal, chop the throttle and it floats slowly down to normal, next time it idles high.

ive already made sure the throttle is not sticking. also the air screw dosent have much bearing on the problem. if i turn it all the way in till it seats closed the bike still runs, higher rpm as it gets closed. it will stall after several seconds or after i rev it up a few times when the screw is seated though.

im sure youd like to know the jetting but ill have to look it up tomorrow. bike runs good otherwise, no surging or poping, good power etc. just goofy idle. i have replaced the o-ring for the air screw also but no difference.

thanks

jason

Jason,

I had that same problem on a 200sx quad...The problem turned out to as follows: The rubber gasket used betweent he float housing and the main body was not seated properly...Thus it was leaking a slight amount of air when the engine was idling...only enough air to affect the idle, thus is ran fine at faster speeds...try getting a new gasket and see if that works...good luck...

Jason : That air screw you turned in is a really fuel screw for the idle circuit and it does make a difference. as you said after the fuel is cut off by turning it in the engine dies.

Turn it out 1 1/2 turns. Run it hot and see what happens.If it still has an uneven return to idle turn it out anothe 1/2 turn. If that helps a little go out another 1/2 turn to 2 1/2. You may need to back out the idle stop. Make sure it is good and hot. Now if it is better install a new slow jet 3 to 5 numbers higher and start out at 1 1/2 turns out again. With that exhaust at sea level a 65 or 68 slow and 160 or 162 main may work.

Make sure you have a good clean filter.

Jason : I forgot the obvious. Check every joint on the carb for leaks. The top cap and rubber boots are good leak sources. Sometimes just rubbing some RTV sealant around the top cap joint will seal it right up if it is questionable. If that works then buy a new gasket for when you can get into it.

Still do the slow screw and jetting but make sure there are no leaks first. That includes looking into the diaphram on the side.

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