Having problems with my 1990 kx250

Iv been having problems with my kx250 lately. It keeps fouling spark plugs. I have been reading on some of the these post and all over the internet about my problem. Anyways when I got the bike it was not taken care of at all. The first time I took it out for a ride I did not inspect the bike like I should have(I was new to 2 strokes). The top end had blown up and the rings had seized to the piston and bent the rod. I put a new top end on it and put new seals, bearings, and crank. The bike had done great after I rebuilt the motor. When i try to start it the bike will make a loud pop and the after that it will start right up. When riding for about 30 min I have to adjust the throttle cable so it will idler right. Yesterday i tried to start it and it made the pop sound. Then started. When i started to warm it up it popped 2 or 3 times when running, throwing the granny pipe almost off the springs. also it had blown the O-rings off the granny pipe and died. I removed that spark plug and looked at it. It was covered in black oil and gas(just like the other spark plugs). The compression is 180psi fuel mixture is 36:1 (i do not race)   Could it be burning coolant? i might have re-used some of the fouledspark plugs...is that bad? Or could it be a jetting problem? iv looked at the reeds and there is no crakes. ill take any suggestions. thx

You might want to check your ignition timing; the pop isn't normal.  As far as fouling plugs, you may want to try running about 40:1 with a good quality oil.  Once you see how that goes, then see if it needs to be re-jetted.  I always felt the ignitions on the older bikes just weren't that good.  On my 1990 KX250 (I got used in 1990), I remember changing the plugs about every month.

Ok I'll check that out. Iv tried getting the better spark plugs to see if that would help but i guess not. I use ngk br9eix

You might want to check your ignition timing; the pop isn't normal. As far as fouling plugs, you may want to try running about 40:1 with a good quality oil. Once you see how that goes, then see if it needs to be re-jetted. I always felt the ignitions on the older bikes just weren't that good. On my 1990 KX250 (I got used in 1990), I remember changing the plugs about every month.

Well looks like the tim

Well it looks like the timing was set correctly. When I was testing the spark with the spark plug. It like that spark was yellow is that bad?

Try stock plug which is hotter than 9 series. Br8es.

Did you try leak down test?

I ran br9eix plug yesterday. Did not pop at all. When I got to engine warm it was still throwing some smoke out... Seems like to much smoke

I mean br8eix

You probably have a leaking crank seal, letting in oil from the trans

You need to run at least the "8" heat range plug, a "9" is much too cold for a 250. If you don't ride very hard a "7" may even be called for.

 

You don't change mix ratios to solve a plug fouling issue, plug fouling is caused by rich jetting, assuming the engine is mechanically sound. A sound, properly jetted two-stroke will never foul plugs, and produce no visible smoke when fully warm, no matter what oil ratio you're running.

 

Even the "popping" you describe is likely due to very rich jetting, you're actually getting a rich enough mixture passing through the engine into the pipe while kicking that it ignites in the pipe when the engine tries to fire.

 

I would run 32:1, and start doing some jet testing.

 

This should help you:

 

http://www.thumpertalk.com/topic/1094549-new-to-2-strokes-any-tips-welcome/page-3#entry11748808

Ok I try it out! Hey thanks for all the help guys!

what do the reeds look like?

you set the idle with the idle screw on the carb, not the throttle cable. once the idle is set, you adjust the free play in the cable.

Reeds are not cracked or broken. I adjust the air bled screw about 2.0 maybe 1.50 in that range

Reeds are not cracked or broken. I adjust the air bled screw about 2.0 maybe 1.50 in that range

Also check them for air gap between sealing surfaces. At full rest (removed from bike) they should sit flush. If gap exists they need replacement. 

Reeds are not cracked or broken. I adjust the air bled screw about 2.0 maybe 1.50 in that range

there is the air screw and idle screw. two different things.

there is the air screw and idle screw. two different things.

Yes your right.

Luckily I bought a manual to go with this bike. Helps out a lot

Then let me ponder the question as to why you are still using the cable to adjust the idle? Or did you just not know the difference? Seems to me you are having serious jetting issues. I would take and buy a cheap batch of 8 range plugs (BR8cheapos) and use those until you get your jetting proper then use the EIX labeled ones as they are about 2-3x the price of standard plugs and for the sake of this job they do just as well. Your bike probably has the infamous TM Mikuni.. Good luck.

carb.jpg

Well my kawasaki parts place does not know much of anything about jetting. Iv pulled the bottom of the carb off and I was going to put a leaner jet. The jet I have now is #158. The bigger the number the bigger the jet right? Iv got plenty of plug for testing

Hold on a sec.

 

First off, you need to put the right plug in there: BR8ES.  

 

Then ride it and see how it is.  If it's still not running right, pull the carb and the jets from the carb and post the numbers.  Also, what is the clip position?  There is a process to fixing things, you can't just throw mains in there.  lol

Yes I have put the plug in there and run it around. Then I pull the plug and it was black just like the others. I have not adjusted the throttle cable. Only to get slack out

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