Posts
132
Joined
4/7/2011
Location
Grand Prairie, TX
US
Edited Date/Time
5/19/2015 8:15am
I recently purchased a 2014 YZ 250 and let's just say I love it. Best stock bike I have ever ridden in my opinion. Anyways the thing has about 15 hours on it and now has a major bogging/ sputtering problem. I am a pretty aggressive rider and usually burn through 3-5 gallons of fuel during a day of riding. Since I've had it I have mixed it 36:1 with Maxima Castor 927 with just pump 93...I know, get race gas. Oil and air filter is done every ride and sometimes a filter change in the middle of the day. Air box is always clean and fuel is always fresh. When I'm warming it up it sounds good, has pretty good hit and revs good. When I actually start riding he bike is OK off the bottom and then during the mid it is empty. Bogging and sputtering galore! Sometimes on a good straight I'll just hold it wide open to clear it out and sometimes is will for a second and sometimes it won't. By the way, this has only been happening for the last 2 rides which has equalled about 30 minutes. Something I have tried are switching jets, spark plugs, race gas and NOTHING gas worked. Any ideas guys?
Is the ignition timing adjustable with the stator plate? If so, make sure it hasn't moved. I'm not sure if it is, I waste most of my life working on fat peoples Harleys.
Perform a compression test to make sure you haven't killed the piston.
I know you said you always run fresh fuel but just make sure there is no water in the gas, anything could happen.
Air leak at the crank seal behind the flywheel could also make it run stupid.
If all this checks out I would say its a jetting issue and would suggest spending some more time swapping jets, adjusting the needle clip position and air screw.
I would do all othe stuff above but if you dont find anything obvious start tearing it down. Jetting doesn't randomly change on brand new bikes with 15 hours.
The Shop
I t actually sounds like a very small air leak. I've found that the method of spraying ether/wd40/propane/etc all over the motor doesn't work very well when it's a small leak.
I created a leak down tester from about $15 worth of stuff from Lowe's. PVC pipe that fits into the intake boot with teflon tape wrapped around it to make it a snug fit. Expanding freeze plug for the exhaust port and a bolt shoved into the power valve vent. Used a gauge with a schrader valve that I picked up in the natural gas section; attached right to the PVC. A couple of pumps with a bicycle tire pump, some soapy water and you're good to go.
Last week the bike ran for a full 20 minute practice with no issues, then in the second practice the bike started spitting and sputtering with nothing done to the bike between practice. Then I could tturn the bike and then go ride it in the field for about 3-5 minutes running fine and the start sputtering again.
Here is what I have changed/inspected so far. This has been going for about 2 months.
Both crank seals - no difference, Changed gas more times than I can count - no difference, checked reeds with no signs of wear or fatigue, cleaned the carb to many times to count. New rings with a compression test, motor looked brand new (it has less than 20 hours on it. Changed spark plug cap - no difference, changed pipes - FMF, Pro Circuit, Stock - no difference.
Last night I took the stator off of a friends bike and tried that, this solved the problem (but hold on) I rode the bike before the stator change and the bike was running terrible, changed the stator and now it runs great.
After testing I put my old stator back in to confirm that indeed it was the problem and now the bike runs great with the old stator back in. Rode the bike for a good 15 minutes with no issues. My son seems to think it does not pull as good with the old stator but I could not tell any difference.
Also a friend of mine who is a respected mechanic said he has heard of coils doing this and for me to check that next.
As of right now the bike is running fine, we will see when we go for our next practice session.
Any help on this would be appreciated because if this does not work, I am at wits end.
I put the other stator back in and the bike instantly perked up and my son got in a 20 minute session with no issues. We will see of course but at this point I would check you stator with one off of someones bike. They are pretty easy to get off and on if you have a flywheel puller and you can get to the harness without removing anything. Takes 5 minutes with the puller.
I'll be ordering one tomorrow but will keep you posted if it reverts back to not running.
Thanks for the input though
Pit Row
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