We got the cylinder off of the 400ex a minute ago and we didn't see what we expected to see. The piston, rings and cylinder all look perfectly fine with the only exception being the spark plug & valves area. They were solid black and almost completely covered with carbon. Brand new spark plug with 20 -30 minutes is completely black as well. What could be the problem? I was expecting a scored cylinder and rings.

The only thing I can think of that might be the culprit was the previous spark plug was not all the way in. For those that might have forgotten, the previous owner has stripped the spark plug hole and when we pulled it out, we might not have screwed the new one in far enough.

OK, Brainiacs, help us. We're taking it to the dealer in the morning to have them look at it and then we'll take the cylinder head off to the machine shop to fix the spark plug hole so it's not like we tore it apart for nothing.

Kyle

 

might be the cdi, air usually means lean

 

What??? There's no mechanics on here?

Anyway, we took it to the machine shop and it will need to be bored. Hope to have it all back together by next weekend.

 

Ok so, pretty much your saying your bike is to rich.... You answered your own question guy.

How did your bike run before you took it apart? need details

 

You see the cars everyday, you know the ones with no paint, no shocks and you can smell them miles before you get to them? Then as you get closer, you see plumes of blue smoke. That's how pretty much the engine was running. Having never ridden one before we didn't have anything to compare to and racing side by side with my 350X, it was neck and neck.

It started out, it would sputter and generally wasn't running right. Turned out it had a 160 main, replaced it with a 145 and it ran great with no airbox restriction. Install ALL of the plastic and it wasn't quite running right. Smoking got worse by the minute practically. I think the fellow didn't take care of the air filter and it inhaled too much dirt. The fellow at the machine shop said it was out by 0.007" so he'd probably have to bore it 0.020" over.

What we've decided is to have it bored and will install a new piston and rings and go from there. Hopefully it all should be ready next week sometime and we'll reinstall it on Friday night or Saturday and see what we've got.

 

I hate to tell you this but the problem is most likely the carb has a problem... or your putting to much oil in it.

 

Please elaborate some more.

The cylinder was worn though. It had a good sized groove at the top and you could feel more inconsistencies farther down Where else could the oil be going besides past the rings, which it was definately going out the exhaust. After all of this is done, he should have a good as new top end.

Now tell me this, stock main is 148, we're running a 145 currently. We're at 4,000' elevation. We're most likely going to need a larger main jet now aren't we, likely stock size?

And I have another question, on the left side of the carb is a screw. The screw lies parallel with the ground. What does it control? When opened up, it leaks gas out the vent hose nearby.

 

With your high elevation (4000 feet) you need to just leaner due to less oxygen in the air, hence the need for less fuel, not more fuel.[img]i/expressions/face-icon-small-smile.gif[/img][img]i/expressions/face-icon-small-wink.gif[/img][img]i/expressions/face-icon-small-smile.gif[/img]