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Bike Revving by itself????

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Ok, I took the 2003 KX 250 out for its first test run since rebuild. Everything was good and the bike ran great! The only miss-happ was in the first 5 minutes of heading out into the trails.

I was running along at about 5-10 mph first gear 12/48 gearing and the bike the bike started to rev -up by its self. So I hammered the throttle forward and pulled the clutch in yet the bike still was revving. I sat there like this stopped with the bike topped out for a few seconds before it came back down to idle.

This kinda made me vervous for the rest of the days ride because I didn't know if it was going to do this again.

Jetting seems spot on running 32:1 and no spooge out the rear. The bike starts up first kick and idles great with the 13oz FWW.

So any takers on what the issue is?

The throttle is nice and snappy on the stand and it dosnt seem like a sticky cable.

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double check cable routing. check for proper action with bars locked to either side. it's easy for the cable to get pinched the way it is routed next to the tank. My cables have always frayed were it makes the sharp bend into the top of the carb.

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Could be a throttle cable as mentioned above, also sometimes the throttle assembly needs to be taken apart cleaned and lubed so it shuts quickly when you release it. Also lean jetting or an air leak can cause surging or hanging idle.

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Another thing you could check is free play in the throttle adjustment, similar thing happenned to me and the throttle adjustment was too tight.

Cheers Jas,

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I ran highrisers on my KX, but kept the stock cables, big mistake, whenever the bars moved the throttle open up a fraction and the bike revved, took me awhile to figure it out, :)

as the others say, check your carb, set all the setting to stock if you are running the stock settup on the engine and check your choke.

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Step 1: take your hand ALL the way off the throttle,

if this fixes it get some gloves that fit

Step 2: take the throttle off the bars and clean, clean, clean.

once clean inspect, inspect, inspect. there could be grit in the throttle tube or cracked or damaged throttle tube.

while the throttle is off and apart take the throttle slide out of the carb and blast WD40 through the cable till it is clean, then lube the cable with a cable lube. inspect the cable at the throttle and carb ends, frayed cables are bad (6 weeks in a wheelchair because I neglected mine)

Step 3: pop the clean throttle tube and lubed throttle assembly back on the bars and check the throttle action, also take time to check the throttle cable routing.

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also sometimes the throttle assembly needs to be taken apart cleaned and lubed so it shuts quickly when you release it.
Step 3: pop the clean throttle tube and lubed throttle assembly back on the bars and check the throttle action, also take time to check the throttle cable routing.

Never lube your throttle assembly. If there's lube in there dirt has no way to work itself out and you'll wind up with a sticky throttle. The only part that could have a drop of grease on it is the bushing in the center of the wheel. Everything else should be dry as a bone.

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Never lube your throttle assembly. If there's lube in there dirt has no way to work itself out and you'll wind up with a sticky throttle. The only part that could have a drop of grease on it is the bushing in the center of the wheel. Everything else should be dry as a bone.

This is a fact. Dry throttle assemblies are happy throttles. I only lube the cable.

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I had a similar problem with my 2002 L4 and what it turned out to be was i had inadvertantly snapped the bent tube that feeds the cable into the top of the carburetor. The reason this happened is that instead of pulling the carb off to change the jets i was just twisting it round (after losening the jubilee clips) so i could access the float chamber on the bottom and it must have cought on something and broke, DOH!

Unfortunately you can't just replace the tube as it is part of the top chamber, only cost about 20 quid for a new one though.

Hope this helps,

Mike.

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1 other thing to check, is your air filter sealed against the air box. I took my filter out for a look forgot to screw it in tight and the engine was revving high for a while. Didn't wanna come back to normal idle.

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