250EX Problem

[250rAL]

I'm hoping someone can give me an idea which way to go in diagnosing a problem with my son's 2003 250EX. When you try to accelerate in the midrange, about half throttle, it stumbles. It does fine below that and if you can get above that it will go full speed. The machine doesn't have very many hours on it and is completely stock. So far, I've replaced the plug and cleaned the carb(blew out the jets). The valves were adjusted about a year ago. The filter is clean. I was going to go richer on the needle but came to find that it was at the bottom notch already(stock apparently). I tried one leaner but it was the same. Since it's only in the midrange, I find it hard to believe it's not a carb problem. Can something electrical only affect the midrange like that?

[Sjorge450R]

Originally posted by 250rAL
I'm hoping someone can give me an idea which way to go in diagnosing a problem with my son's 2003 250EX. When you try to accelerate in the midrange, about half throttle, it stumbles. It does fine below that and if you can get above that it will go full speed. The machine doesn't have very many hours on it and is completely stock. So far, I've replaced the plug and cleaned the carb(blew out the jets). The valves were adjusted about a year ago. The filter is clean. I was going to go richer on the needle but came to find that it was at the bottom notch already(stock apparently). I tried one leaner but it was the same. Since it's only in the midrange, I find it hard to believe it's not a carb problem. Can something electrical only affect the midrange like that?

sounds too rich on the needle. Bring the clip down somemore.

[300ex_#387]

I would think it would be electrical. Mine just went into the shop for a new ignition coil, because it was doing exaclty that. Might want to look into that.

[250rAL]

I've been researching and apparently if the flywheel key is sheared,and the timing is off, it can cause exactly those symptoms.

[ryanh250ex]

Originally posted by 250rAL
I'm hoping someone can give me an idea which way to go in diagnosing a problem with my son's 2003 250EX. When you try to accelerate in the midrange, about half throttle, it stumbles. It does fine below that and if you can get above that it will go full speed. The machine doesn't have very many hours on it and is completely stock. So far, I've replaced the plug and cleaned the carb(blew out the jets). The valves were adjusted about a year ago. The filter is clean. I was going to go richer on the needle but came to find that it was at the bottom notch already(stock apparently). I tried one leaner but it was the same. Since it's only in the midrange, I find it hard to believe it's not a carb problem. Can something electrical only affect the midrange like that?

I just discovered this thread.


I've messed with the jetting a ton with my '02, i know for a fact that there is a total of 6 different positions on the e-clip of the jet needle. stock is the 3rd position. i would try 1 notch lower on the needle (making it richer). these bikes are made as lean as possible from the factory to appease the emissions folks and it comes sometimes at the cost of performance and even ridablility.

[250rAL]

I don't know about the '02's but our '03 only has three clip positions. I replaced the plug and readjusted the valves to no effect and then as a last resort, I took off the airbox lid and tried it. It worked! I ended up drilling some holes in the lid for a permanent solotion. I still can't figure out why it suddenly went rich when it's bone stock and nothing has changed. I thought maybe wasps had built a nest in the snorkle but since the snorkle is clear plastic, I think I would have seen it when I adjusted the valves. Oh well, I like free fixes.