idle surging: 2000 250SX

[SUSPENSIONTECH]

I tried searching but couldn't find anything, the problem i'm having is after the bike reaches operating temperature the idle starts surging heavily(prob. 4-5k tops).

I'm thinking maybe vacuum leak, but nothing ovious was found.

Just wondering if anyone else has had this issue, and if there is a quick fix or what needs to be done.

the bike is all stock, it's fairly new to me... it did sit in storage for a couple years from the previous owner

[SkiDaddy]

Spray carb cleaner around the cylinder base, carb boots, etc. & listen for a change in RPM/note. That's one way to find a leak.

It could also be a crank seal. Pull the ignition cover & spray WD-40 around the area.

[Mike in Fresno]

start the easy stuff first. Turn the air screw in a turn or two while it is surging and see if it makes a change. Take carb off and clean pilot jet. Since it was sitting this could be partially plugged and its common with the gas we have now for this to clog. You need to know what jets are in there anyway. After that start thinking air leak.

[SUSPENSIONTECH]

OK well I've tried all the stuff stated above, and it is still surging when at operating temperature, also I found that when it is surging the kill switch is not working, but works fine before the bike completely warms up.....

[Mike in Fresno]

well, if its surging as in like a stuck throttle then the bike could be dieseling and the kill button wont work then, but it would have to be a wide open thing. Excess carbon on top of piston can get red hot and cause the engine to keep running also, but a 2st usually doesnt get that hot. Im not sure what it could be.

[SUSPENSIONTECH]

checked throttle cable & carb, its closed. engine is running fine, it surges bad after warmed up. noticed that kill switch is inop also. have the factory manual-with no help in troubleshooting guide. I'm leaning toward a cdi unit but I hate to guess. thanks guys.

[40oz]

Wow, seems dang similar to what I just (as in the last 2 days dealt with).

Same symptoms exactly. mine was a super easy fix.

Try this:

Unhook the throttle cable from the slide that holds the needle....take it totally out and put the slide back in and close up the carb (this will allow the slide to FULLY sit at the bottom of the carb.

put the rest of the bike back together - just enough to fire it up. Kick the bike and see if it idles better.

if it does - hook the throttle cable back into the slide and close up the carb as you normally would. fire the bike up see if it goes back to the way it was.

if there is a difference then its the throttle cable.

Now unhook it from the throttle housing and fire it up, check for a difference in idle.

.....

What I ended up doing that fixed the problem was loosen the nut on the throttle housing and adjusted the tension there and it worked like a charm. I then put the air screw and idle screw back where they were and fired it up (i probably let it run a good 20 mins and all was good) took it for a ride today and it is back to where it was previously. I am guessing during my last race when I picked the bike up in the mud (it was a ultra mud run) that I tweaked the cable a bit.

** I did all the stuff you mentioned as well and some more...I was really starting to freak as I have a race this weekend.

Let us know if this works, or if you cant understand what I am saying. I was side tracked about 30 times while writing this.

[SUSPENSIONTECH]

i have the bike @ work & will try first thing in a.m.

what do you mean "throttle housing"- @ carb or handlebar?

thanks.

[40oz]

throttle housing is the 'throttle' that is on the handle bars - this is were the throttle cable goes into so when you twist the grip, it pulls the slack in the cable and raises the slide in the carb makeing more full enter the engine.

When you look at the carb there is a cable going into it when you take the top off the carb, you will see the cable going into the slide. (right above the needle).

I am sure someone else can explain better than I am doing but I hope this clears some of it up, if not let me know.

[40oz]

Just curious if you had any luck with your bike