Question for all you 250X/300EX gurus

[TRX300X]

O.k. I just got done putting my entire engine together this weekend and in the frame. I did a complete rebuild, top end, resleve, cam, valves, springs etc... All powroll high performance parts but anyway.

I got it running today for the first time, started up on the 3rd kick by the way wich is great. Well I ran the engine once for about 10 seconds and then shut it off to check for any oil leaks which there were none. I then started it up again and reved it about a quarter throtle for about 15 seconds and then shut it off. Well both times that I ran it black smoke blew out the exhaust, I dumped oil in the cylinder when i put the top end together to lube it so I'm sure thats where the smoke came from. Now when I shut the engine off something kept turning after I killed the ignition. By the way I did not have the countershaft sprocket hooked up to the chain. By the way the tranny shifts buttery smooth.

So my question was the turning noise just the grears in the tranny freewheeling or what could it be?

Also I tired to start it again and I seem to have lost spark. It looks like I don't have any power comming out of the stator. Is there any way to test the stator or are there any specific places I should look that would cause a loss of spark.

[300exazzkikr]

The spinning was probably the gears since there was no restriction on it. Black smoke is usually related to running rich. I would do a plug check and what the carb is running like.

[TRX300X]

I bet money that the black smoke was from the oil i dumped in the cylinder when I put it together, there's no doubt in my mind about that. I know I need to rejet some more but I'm working on getting it to actually run for right now. But I'd still like to know about my spark related problem that I described in my first post.

[300exTJjeeper]

I bet your not getting a spark, because the plug is covered in oil. Unless that is you changed the plug after the all the oil in the cylinder was burned.

[Bill Fuller]

Have you changed plug yet?You do know how to check for spark don't you(not trying to insult you at all)I bet with a new plug you should be fine,hope I can help.

[BS300ex5]

i experienced somthin very similar... it was smoking after all the oil was burnt out and it was hard to start sounding flooded when it wasn;'t... the carb was right and everything was the same scenario as you... when i took it apart i found that that lil bit of oil i dropped down in the cylionder collapsed one of my rings and oil was leaking past the rings (hope yours is different than mine but just another option)

[TRX300X]

As far as rings and compression go the rings are fine and the compression is fine. I did a leak down test and I have like 7% leakage past the rings. I'm not concerned about the smoking but what I am concerned about is the spark. I've put a new plug in it and done the spark test. That was the frist thing I did. I went through the electrical system and from what I've been able to find with my test light I have no power comming out of the stator. Is there any way to test this for sure without replacing it with a known good part?

By the way thanks for all the help you guys have been giving me, I appriciate it.

[300exazzkikr]

Originally posted by TRX300X
As far as rings and compression go the rings are fine and the compression is fine. I did a leak down test and I have like 7% leakage past the rings. I'm not concerned about the smoking but what I am concerned about is the spark. I've put a new plug in it and done the spark test. That was the frist thing I did. I went through the electrical system and from what I've been able to find with my test light I have no power comming out of the stator. Is there any way to test this for sure without replacing it with a known good part?

By the way thanks for all the help you guys have been giving me, I appriciate it.


You can test it with an amp meter. If you get a service manual it should say how many amps the stator should be putting out. I don't have one so i can't help you there. Someone must have one that could look it up for you.