Help CR250 problem.?

The klotz synthetic is ok at 50:1, and is recommended at this mix ratio.

Have you checked your reeds? Sometimes a cracked reed can cause jetting issues.

Otherwise, I agree with the o/p, especially if the bore kit uses a steel sleeve and not a nikasil bore. These wear more quickly.

Also the K&N filter, although they're the perfect option for endurance racing, don't really filter as well as the foam filters - so you usually see a bit more piston wear when you're running one.

Check the reeds first - look for feathered edges or cracks in the petals. Replace if they're bad.

You mention a Mikuni carb - not stock. Did the bike run properly with this carb at some point, or have you always had problems? If this is ongoing, then the carb could just be set up completely wrong for your engine - there's so many variables (pilot, air/fuel mix screw, needle, needle jet, slide cutaway, carb throat volume, etc, etc), that if it never ran properly, I'd try jetting your stock carburetor about 5 sizes bigger on the main, and move the clip down one position on the needle. Try this setup, and see if the problem goes away.

If this doesn't solve the problem (or the bike did run well with the Mikuni, but just got bad recently), then do a compression test. With your setup, you should see at least 150 psi, probably much higher - check your shop manual for the stock minimum number, then add another 20% for your bore/stroke increase. A low reading means its time for a top end rebuild (and a crank health check while you're in there).

oil filter oiled too much??? WTFFFFF???! LOL! You must mean air filter bro.... I'm sure that's what you meant. YES, you should check your airfilter, clean it or replace it. I dunno what size needles or positions you tried? If it's jetted for 50:1 it's no problem at that ratio...hmmm, I'd maybe see about running a different temperature spark plug, replacing the reeds, or rejetting. The last thing you wanna do is a top end rebuild, since that's the most work, but that could easily be what it needs. How long have you had this 330 big bore kit? if it's been a while, you more than likely need new rings or bore/piston/rings...I just hope there's room left to bore...

BUT, you didn't say how often it's fouling plugs. 2 strokes foul plugs no matter what, if it's only lasting a few hours days it's a problem, but if it's every month or two, I'dd say that's normal. It's always nice to throw a fresh plug in there...another thing is how you ride it, if you just putt putt around real easy on it like trail riding, it'll foul quicker, if you wack the throttle on/off it'll last longer.

Either the oil filter is over oiled, or the top end is worn out. When was the last time you changed the rings?

50 :1 is way to lean of a mixture. That would ruin your top end.

Remove the exhaust pipe and look in the exhaust port with a mirror and flashlight. Any scoring of the piston or cylinder wall will need repairing. Also discoloration below the rings (blow by past the rings, from being worn out).

If the exhaust blows a lot of smoke, then it might have a leaking crank seal.

the sole element i recognize of which will reason 0 compression is a hollow the two interior the piston or cylinder. if it quite is the cylinder it can't be repaired. no count if it quite is interior the piston then all you will be able to desire to do is replace the piston and rings and clean the steel out of the case. whether in case you broke out the valve chamber it would provide you 0 compression, that would desire to be mounted by potential of cleansing each and all the steel out of the case, changing the piston and rings and changing the entire precise end inclusive of valves. Edit pass with Janice's suggestion!

That motor needs to run wide open most of the time,otherwise you will foul plugswhen it idles or is run slow too long.Try a step hotter plug.

well you could try a different spark plug grade .........but do you give the bike a shake before riding it to mix the oil in the tank? cos it will sink to the bottom when ya park up

I ride a WCX360. 50:1....kills my bike and plug....that is a $16 plug too....replacing those every 4 to 6 hours is pricey...I now run it 32:1....and it rocks! (oh, and a $9 plug)