03 RM250 troubleshooting

I am trying to help my uncle fix his bike and not having much luck. I decided it was time to see if you all could help. I apologize for such a long post.

I went with him to look at this used 03 RM250 two stroke. I noticed it was running rich on the bottom but figured it was probably as simple as jetting. You could run it through the gears at wide open throttle then turn around to come back, and it would be loaded up again. It clears out at wide open throttle but loads back up when you let off for any amount of time. He liked the bike and it seemed like a great bike other than that so he bought it. The bike appears to be bone stock other than a pro circuit pipe and silencer. My Uncle is a beginner level rider so he was fouling plugs right away. Pulling the carb off revealed that it had stock jetting. I know it should run fine and not load up on stock jetting but decided to try leaning it out with the main jet. I ended up with it being to lean per a plug check but still loading up on the bottom. I tried lowering the pilot jet and raising the main jet but nothing fixed it. The float height was set with the float slightly below level, with the bottom of the carb, when the needle came in contact with the seat while holding the carb upright. He did not ride it hard and it was a little bit better so he rode it this way and simply cursed it every time he had to push it back to the truck.

I then decided it must be sucking tranny oil through the right side crank seal. So I put new crank seals in it without splitting the cases and put a new top end in it while I was there. It still did the same thing. One thing I noticed while putting it together was that I had to twist the rubber exhaust pipe mount (lower) to make it fit. Otherwise, it was to long. I thought maybe it had the wrong pipe mount but I compared it to another bike with a stock exhaust pipe and it was the same. This makes me think it has the wrong pro circuit pipe and maybe that is causing it. However, the pipe fits great other than that, and it is definetely a 250 exhaust pipe so I doubt that is the problem. I played with the jetting a bit more as well at this time and we had it to where it did not foul plugs, but still loaded up on the bottom slightly. He rode it for a while like this.

It got worse and started fouling plugs so I decided the only thing left was that it had to be leaking between the cases. So I split the cases the other day and inspected the gasket and did not see any signs of it sucking oil into the crankcase so I do not think that is the problem. I did notice that the cranshaft will slip right into the right side case by hand. It feels tight when it is in there but I think they are supposed to be pulled into the bearing and not simply slip right in? I had another bike with the crankshaft the same way and it did not have this same loading up problem so I do not think that is the problem but could be I guess.

Keep in mind, each paragraph or attempt to fix it above happened months apart and the bike was being ridden between so that rules out a gas problem. He is running Silkolene Comp 2 premix at 40:1. I am starting to think it must be in the carb like maybe it is a stuck float or a leaking needle and seat but shouldn't it be overflowing with gas? It is not. I have inspected the carb many times and do not see any problems. I have completely run out of ideas. Any suggestions? Thank you for taking the time to read this and for any suggestions you might have.