Maintenance & Technical > KX250 / KX125

1979 KX250 Stock Carb Specs

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Foxx4Beaver:
the 1st thing you wanna do is determine why it's idling high....it could be as simple as just needing to adjust the idle screw...or you could have an air leak, which would be a problem.

Is the idle erratic(rpm's up and down), or is it a steady high idle?

I would inspect the intake manifold area really well, for cracks in the rubber, and any oily wet areas anywhere around the motor.
once you're sure that's taken care of, and there's no air leaks...then yeah, start off with what jets are in there. You'll need to do some WOT plug chops...that will help determine how close, or far off the jetting is.

ctharre:
As for the type of idle, I recall it was a steady high idle- not erratic.

I actually had a similar problem with a high idle on my 75 yamaha dt250. It would run normal until it got the engine warmed up it seemed, then it would start to do a very high idle and sound like it was gonna keep revving faster until the piston flew off!  I replaced the crankshaft oil seals for that and I haven't had the problem since.

I've got this bike to the point where it really wouldn't be that much extra work now to replace the crankshaft seals, so I actually just ordered the pair and will be doing them soon here (besides, i'm in iowa, so riding is still another month or two out).  Also I have already replaced all of the other gaskets- so hopefully I will have any air leak problems taken care of and it will just be carb adjustment this spring. 

As for the intake manifold-  mine looks a bit gnarly from the outside, but I have looked at it closely on the inside to see if any of those surface cracks on the exterior make it all the way through, and I did not see any at first glance.  I will check this out again to be sure. 

Now back to the gnarly exterior- I was thinking of buying a tube of high temp silicone to apply over the whole outside and hopefully seal up the existing cracks and give it an added layer of protection.   Obviously won't be pretty, but this is just going to be a trail bike and the only replacement parts I've seen online are way out of budget.  Any thoughts on this fix idea?

Thanks for the help so far.  I appreciate it.

Foxx4Beaver:

--- Quote from: ctharre on February 16, 2016, 08:37:18 AM ---Now back to the gnarly exterior- I was thinking of buying a tube of high temp silicone to apply over the whole outside and hopefully seal up the existing cracks and give it an added layer of protection.   Obviously won't be pretty, but this is just going to be a trail bike and the only replacement parts I've seen online are way out of budget.  Any thoughts on this fix idea?

Thanks for the help so far.  I appreciate it.

--- End quote ---

that all sounds good...you're going about it correctly by replacing the crank seals...

the carb boot, yes...you can smear it with silicone to get by.
another thing I like to use, that I discovered from friends on another forum, not bike related...is 3M Window Weld...stuff is amazing how well it works for just that reason.
It's a little expensive, but holds up very well...just gotta scuff up the boot really well, then give it a good cleaning before applying...

ctharre:
Nice- I'll take a look for it at Menards tonight... then straight to the garage for tinkering!

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