[Simon Stdt]

Hey guys! I recently bought a 2007 YZ250F which doesn't start. The owner said that one day she just wouldn't start anymore. He also said that he has changed the spark plug and she does have a spark, I saw that, I'm just not sure if the the spark is powerful enough but I think that should be fine. When I checked the carburetor there was gas pouring out of the overflow hose. I brought the carb to a Yamaha dealer who cleaned it in an ultrasonic cleaner and put some new seals in. Today I put the carb back in but she still wouldn't start. I even tried push starting. I checked the spark plug and it wasn't really wet. And for testing I didn't put the air filter back on so that shouldn't be a problem either and I also put quite a bit of fresh fuel in the tank so it isn't too nasty. Thanks for the help in advance.
Simon

 

[Warrior_Scott]

Hey guys! I recently bought a 2007 YZ250F which doesn't start. The owner said that one day she just wouldn't start anymore. He also said that he has changed the spark plug and she does have a spark, I saw that, I'm just not sure if the the spark is powerful enough but I think that should be fine. When I checked the carburetor there was gas pouring out of the overflow hose. I brought the carb to a Yamaha dealer who cleaned it in an ultrasonic cleaner and put some new seals in. Today I put the carb back in but she still wouldn't start. I even tried push starting. I checked the spark plug and it wasn't really wet. And for testing I didn't put the air filter back on so that shouldn't be a problem either and I also put quite a bit of fresh fuel in the tank so it isn't too nasty. Thanks for the help in advance.
Simon

If you have fuel and spark that pretty much leaves compression.
Well, exactly how does the spark look? any blue color to it? If it has some blue it should be good.
Make damn sure the plug is dry and clean too.

 

[Mudline Motorsports]

Simon I agree with Warrior_Scott, if there is spark and fuel than that only leaves one culprit - compression.
You wont be able to do a compression test on this bike because of the auto decompressor but you should be able to tell if there is a lack of compression just by kicking the bike over. Compare the amount of energy it takes to kick it over to another 250 if possible. Another way to tell is If you are able to use your hand to push down the kickstarter and it doesn't require much effort then it probably needs the top-end rebuilt. Keep us posted, I will be keep an eye on this thread.