KX goin CRAZY!!!!!!

[REARWHEELSLIDER]

Ok now.


91 kx250. Recently purchased this vehicle from a good owner. I do have a problem though....


Every time i attempt to start this machine, it revs really high, then after about 10 seconds(which feels like eternity) of revving itself to the moon, it dies back down to a kinda normal idle. I wonder what could be happening, and i hope its not a lean condition because we all know wat even a few seconds of leanage can do to our bikes! There is pleanty of blue smoke upon the startup though, so i dont suspect lean conditions. It only does this when cold, and choke on, but when its revving itself to the moon, i try to shut the choke off, and absolutely nothing happens, not even a change of engine revs or tone. So maybe the choke is broken. I dont know...

:bang:
Other than that, the bike runs great! Lots of power, and seemingly a normal/slightly above normal amounts of blue smoke when hot. Maybe jetted a little bit too rich, but i dont think thats the culprit of this issue.

Thanks everyone.

 

[SirHilton17]

hmm..
Check to make sure that there is no air leaks around the carb, reeds cyl base, and cases...

Try cleaning your carb too.

I wouldent sugjest for you to keep riding it, because really high revs on a dead cold engine is very bad for it... if you continue to start it with it reving like that it will cold seize, when a bike cold seizes it usualy will not lock up solid, but you run i very high risk of the cylinder plating chiping off.

 

[REARWHEELSLIDER]

Where the heck should i start? I know the carb isnt perfectly jetted. But what would/could effect a cold engine like that? ONLY when cold, is whats gettin to me. Could the powervalve be stuck open when cold, could there be a very miniscule air leak, then when it heats up, it seals? I dunno. Please help me. Carb problems?

Help!!!!!

I need to go ridin this weekend!

 

[i_955]

Start it with the choke on, it starts to rev, turn choke off, revs reduce, raise choke, bike starts to rev, turn choke off, revs reduce, turn choke on. Repeat until engine is warm.

 

[SirHilton17]

Start it with the choke on, it starts to rev, turn choke off, revs reduce, raise choke, bike starts to rev, turn choke off, revs reduce, turn choke on. Repeat until engine is warm.

thats what i do...

if i dont turn the choke off and on it will rev high as beans

 

[elcamino12sec]

I have the same problem with my 1994 kx250, I have the clutch side crank seal but have not replaced it yet ( no time ). I sprayed starting fluid on all the gaskets, seals etc. also behind the magneto for the other side crank seal and no change in revs while running. My bike also smokes while its reving upon start up (only while cold ). I have had no time to change out the clutch side crank seal yet, the last time I rode I started it in second gear, that seemed to make it normal. I know this is not the way to cure the problem but I would rather do that than have a cold seizure until I have time to change out the seal.

 

[REARWHEELSLIDER]

Oh ****! Mee too! I wonder what our problem is.....

I usually start it in second to tame the revs using clutch. Better than a cold motor overrrevving..

So what is our problem?

Anyone?

 

[TimberPig]

Oh ****! Mee too! I wonder what our problem is.....

I usually start it in second to tame the revs using clutch. Better than a cold motor overrrevving..

So what is our problem?

Anyone?

Well elcamino12sec knows he has an air leak at his clutch side crank seal, which should be replaced to solve the problem of it sucking air there, and remove the possibility of a seizure caused by lean running. You haven't tracked yours down for sure yet, but yours is probably the same cause. Both of you need to tear it down and replace the seal (provided yours is leaking at the seal) to cure the problem and eliminate the potential for the engine to seize from lean running.

You can quickly and easily tell if you have an air leak by pressure testing the crankcase.

Here is a thread with directions to build a tester for cheap.

$17 Leakdown Tester thread

To test for leaks, you plug the intake and exhaust, pump up the tester (max 15 psi), and see how much leakage occurs in 10 minutes. 1% per minute is acceptable, any more, and you need to find the leaks. If your seal is blown, pop out your oil fill plug and you will most likely hear the air escaping.

 

[REARWHEELSLIDER]

Okay! Today, i checked out the kx, and came to a great conclusion!

I determined that my intake manifold boot os cracked. I have the boyesen rad reeds w/ the replacement rubber boot too. I had to rtv/silicone some of the cracks and make it seal good, and cleaned the carb(pilot was clogged), installed new vent hoses, and bam, she started like new, no high revs. Boyeson wanted 70 bucks for the book, so i said **** it.



Thanks!!!!


rws

 

[REARWHEELSLIDER]

Hey, another question, is it ok for my cylinder to have some visible score marks? Nothing you can feel, just looks a little shiny in some spots of teh cylinder wall. The piston looks good, though....


Tell me what you think!


rws

 

[TimberPig]

I'd start looking for a deal on a new boot. The silicone will only hold for a little while, particularly since fuel vapours break down silicone, causing it to fail. It is only a matter of time before it fails again, possibly causing at least twice as much damage to other engine parts. A top end alone is about $125-$150, just for a piston kit and gasket. A $70 boot is cheap in comparison.

On the cylinder, if there are no spots that catch a fingernail, and the plating is all intact, I wouldn't worry about a couple shiny spots. A cylinder can look pretty bad, but still run fine after honing. It doesn't sound like yours is anything to worry about.

 

[Bodge]

my rm does this, just tap the kill switch untill you can get to the choke knob.

 

[windyhill]

My 04 does the same thing, has since it was new. I was talking to a very good mechanic in my area the other day and he mentioned this problem is inherent on KX's.Unfortunately I can't remember what the reason was, other than something to do with the carb.(How's that for stating the obvious!).
Anyway, I just modulate the choke a bit until she warms up. John.