bike died while riding and wont start??

I am helping a friend that has a 07 kx250f. He was just riding along at a moderate speed and the bike just died. From the description it sounded like it was electrical like it lost spark. Checked for spark and that seems good. Carb is getting fuel and it seems that a fuel related problem wouldnt have died so suddenly. I noticed that I can fairly easily turn the engine over by hand with the kick starter. Almost seems that if the bike were running properly that I could start it by hand. I am used to bigger bikes, is this normal for the kx 250f or does that seem like low compresion. I am planning on adjusting valves and doing the routine stuff. Would like to know why it suddenly died and why it wont start before I start tearing into it so I know what to look for. At least have some hints of what to watch for. I am not real familiar with the kawis. What do all of you KX gurus suggest that I give attention too.

Well, you've checked for spark and fuel, and obviously it's getting air, so that doesn't sound like your problem.

My guess is that it's something internal. Did it make any loud noises before it died?

I could start my 06 by hand when it was fairly new, so I wouldn't worry about the lack of compression too much, but it does sound like you are going to have to tear into this thing to find out what is really wrong.

Thats what I was affraid of. Thinking that it could have possibly sheared the flywheel key. Which would still show spark. Just at the wrong time. The owner didnt notice any noise when it died. He did comment that when they were towing it back that they noticed smoke coming from what he thought was the carb vent hoses. That sounded a bit strange, not sure what to make of that though, (or if that was actually where it was coming from)

The smoke was probably coming from the crankcase breather hose (which is routed right with the carb hoses). That's not a good sign.

check compression...something could have let loose and holdng valve open...

won't have no compression...

my 2cents

Or the piston cracked straight across.

Are these bikes prone for any certain things? or just the typical 4stroke stuff. Seems like they all have a weak link somewhere in the engine. Just not that familiar with the kx lineup. Although I havent checked the compression yet. It does seem to have compression and the owner says it feels thge same as it always has on kickover. Just doest fire. Doesnt even try to start. No sputter at all. Like it is not getting any spark. Guess I am just gonna have to start tearing into it. Let me know if you guys think of anything I should look at. Gonna get a compression guage and start there. What should it have for compression ? Nothing could happen with the elec system besides shearing the flywheel key that would make the spark out of time could it?

Ok, if you have access to a bore scope I would look at the piston see if it cracked accross the top.. This was a designed failure point in oem pistons.

Next if that checks out do a compression test.. you will need to disable the auto decomp to get a reading.. if that checks out I'm willing to bet the cdi went bad.. Bad cdis are not unheard of.. More so in 04s-05s but the 07s are susceptible to cdi failure.

If the cdi was bad would it still have good spark? Can the cracked piston be seen through the spark plug hole with a pen light? Designed failpoint for what? Rod damage? What kind of compression numbers should this bike have? How do you disable the decomp?

Im no kawi guru but the decomp should be bolted on the exhaust cam like most dual cam bikes if I recall correctly it should just unbolt along with the spring. If im right why dont you take a look at the timing and see if its right cam chains do not last forever you know and its along the lines with valve clearance an adjustment anyways . If it skipped time while riding along that could have caused some problems.

You can just wire it in the out position.

Good call on the cam timing. I have the valve cover off now and set at tdc. Valve timing looks good. I need to get a different feeler guage to check clearance. Doesnt seem like valve clearance would ause it to die so suddenly though. Either way, it needs to be checked. I have a compression guage on the way too. So that will be varified.

Does anyone know how much compression is normal?

OK, Heres the numbers. left ex valve .005 right .007 Intakes Left .003 Right .004 compression 80psi obviously the compression is low. Any suggestions or predictions before the head comes off.?

is this in inches or mm? valve clearance should be

● Intake - .004 to .006 in or .1 to .15mm

Exhaust - .007 to .009 in or .17 to .22mm

too tight would explain low compression if you disengaged the auto decompression.

auto decomp is disabled. Measurments in inches Would it die suddenly and not restart due to the valves? Is this far enough out of spec to make it do that? It has been neglected and I hope thats all it is.

My 05 used to do that. it was neglected. the valves were hammering the seats so bad and getting so hot and stretching so far that i could feel it getting hard to start. i would get about 2 hours worth of riding time on a valve job before the valves would stretch so far that the shims would just hold the valves open and i would lose compression in the middle of riding. i even had them stretch so far so fast one time that it actually kicked my cam timing chain back a tooth on the intake side. just a thought.

Everyone that guessed Cracked piston Are the winners. Good job guys. So what kind of sense does a cracking piston as a built in failure point make? What is it designed to protect from? Compression? What is the recommended piston and repair procedure. The cylinder doesnt look to bad. Just light scratches.

Everyone that guessed Cracked piston Are the winners. Good job guys. So what kind of sense does a cracking piston as a built in failure point make? What is it designed to protect from? Compression? What is the recommended piston and repair procedure. The cylinder doesnt look to bad. Just light scratches.

Winner winner, chicken dinner:busted:

I´m not so cconvinced it´s a designed failure point to be honest. But then again, I´m not a Kawasaki engineer.

I just got that feeling from your description, and turned out to be right, HA!

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now