cr 250 running too fast???

[yz_rider_44]

Hey, I have a very odd issue with my 2000 cr 250.

I was out riding earlier this year and the bike was running faster and faster as it got hotter until finally it the bike stuck WOT on me. The throttle was not stuck as i tried killing the engine and even pulled off the spark plug cap to try and stop it but it was dieseling WOT on me. I had to shut off the fuel to kill it.

Did a compression test afterwards, showed me 180 PSI on a crappy tire compression tester. Does this seem a little high?

Im running a stock setup with boyseen reeds, procircuit pipe stock silencer. With a 185 RD main jet.

I had a few cracks in my intake boot, replaced and still seems to get faster and faster as engine gets hotter.

Not sure what to do now, I've only had 1 ride all season and Im really starting to miss riding...

Any ideas, think I'm gonna try 190's in the main??

[Coolidge]

Bad crank seal, Ignition side maybe?????

[Crazyzilla]

You probably have an air leak... but that whole "kill switch didnt work thing" (btw thats some scary shit!!!! Been there done that!) makes me think your running rich (carbon ignites on top of piston making it run diesel-status) and only way to stop it is to kill fuel.

[yz_rider_44]

Ya, bad crank seal... I was hoping it wouldn't come to this.

Ok how can I find out if its leaking through? Or will it be visible if i take a look at the seal? Is that somekind of vaccum test or something I could do?

So, is 180 compression in the normal?

And yes it is scary sh** lol, the bike controls you instead of you controlling it! I'm just glad it didn't stick WOT on the takeoff of a jump or in a wheelie.

[pechinger]

i heard of spraying quick start around the seals and listening for the bike to rev up and if it does there's a leak. never tried it though.

[hillclimbguy]

Just another place to check is the pilot Jet. This happened to me a couple of weeks ago. My bike was getting hot and running on the more I rode. I kept turning in the air screw until it bottomed out.

When I got home I removed the carb to inspect and found that the pilot jet was plugged up.

It was unfortunate that this happened about 50 miles into the ride. Was a long ride back to the truck.

[dmcca]

There are 2 issues... 1. the revs creeping higher and higher... this is probably an air leak or lack of fuel causing it to run lean, and 2. the fact that it runs on without spark means that you've got carbon or something glowing red hot and igniting the fuel once things have heated up too much.

Do a pressure test and determine where the leak is coming from... it could be anywhere... base gasket, head gasket, crank seals, power valve, intake boot, etc... the only way to be sure is to do a pressure test. While you're at it clean your carb to be safe.

Second take off the head and with the piston at TDC remove any carbon from the head and the top of the piston with fine grit sand paper, use a vacuum to suck out the stuff you remove so it doesnt get into the crank.

By the way 180 psi is fine.

[slowthump]

Had the exact same thing happen after a top end job. My lean out episode took out the crank, cylinder and piston. I had air leaks at the reed cage, both crank seals and the top of the carb. Read the sticky at the top of this forum on pressure testing and follow the directions exactly. I made a pressure tester and use it frequently. A small air leak will make jetting impossible and a bigger one will toast the engine.