Hesitation on RM250

[dewme5]

I've got a 94 RM250, that was rebuilt before I bought it. It was running up in Nevada, and now it's down at sea level, and I don't know if the jets were adjusted during the rebuild.

When I hit the throttle in gear, it'll rev up to about 2500, and hit a wall. doesn't matter what gear I'm in. If I keep it pegged, it'll sound like it's hitting a rev limiter for 5 or 6 seconds, and then it'll start running right. It'll come to life like nothing was ever wrong. If I keep the rpm's up, it won't hit that wall.

I've adjusted the main needle leaner, but the situation didn't change, and plug started running white. So, I put the needle back, and I'm back to a good tan color at the base of the plug.

the symptoms seem the same as when spark gap is too large, but if that were the case, it would not rev past a certain point. so that puts it back into carb tuning, or possibly the AETC.

Any suggestions before I start tearing into things?

 

[jake760]

I don't think it's your jetting. Sounds like a CDI problem. What does it do when you rev it in neutral?

 

[dewme5]

It'll rev up easily in neutral. I just wouldn't think ignition would come back to life in higher rpms if there was a problem early on.

It has decent torque off the line, and I can run it almost identically thru the gears. shift, bring it up to about 2500, shift, up to 2500, shift. etc. It's the same in all gears, EXCEPT.. If I pin the throttle, in first gear, it doesn't want to climb into the higher rpms. In second or higher, it will. Which makes me still think carb issues. My thinking is first gear doesn't present enough of a load on the engine to correct itself. Where second and higher load it a little more, and make the conditions more tolerable.

But, I'm not up to speed on 2-strokes, or bikes engines for that mater.

 

[dewme5]

I went out for a little bit with my son this morning. He ended up needing help, and I had to lay my bike on the right side (kick start side) for about two minutes. When I picked it back up, it ran great for about a minute. Then it went right back to the 2500 rpm stumble. So, I tried laying it on the right side again, and got the same results again. I pulled off the stator cover to see if there was oil filling up or?? and everything seemed just fine. It's actually a new part, and there's no oil, or rust on it. the magnet and pickup are in great shape from the looks of it. There is a leak on the output shaft seal, so I need to order a replacement.

I also noticed on cold start up that there was a decent amount of blow-by on the pipe at the exhaust port. I would assume this is somewhat normal until it's warm.

 

[_JOE_]

I would start by ordering a service manual. The simplest thing to rule out is carb. Take it off and clean it like you've never cleaned anything before. Very closely inspect the float valve, needle and slide for wear. Set the float height and re-test.

It sounds as though the O-ring on your pipe where it connects to the cylinder is bad.

 

[dewme5]

I admit, I do not have a manual. I've been thru the carb, and it is super clean. After the results from laying it on the right side, I've pretty much already ruled out the carb. It seems to be a vacuum leak somewhere.

 

[stumanarama]

I would call around around the local shops and get a ballpark of what jetting sizes they use around your elevation, and then check yours. I wouldn't rule out jetting just yet. It sounds like your bike is jetted for the high desert and it's leaned out, and when you lay it on its side your flooding it, and all that extra gas is making it run closer to how it should be.