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What's the deal with my RM??

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For the past few months I've noticed the gradual decline in performance of my 1993 RM250. It babbled, blew smoke, and wet fouls plugs every other ride. When I tried to jet it, regardless of the sizes I increased or decrease it, I found that it really made no difference to the response and over-all running of the thing, it ALWAYS ran rich, even when I had gone down over 10 main sizes from stock. So this immediately made me suspicious of the 14 year old crank seals.

So I decided to do a test. I drained the tranny oil completely and cranked her up. Whallah! Gone was the blue smoke cloud and the thing actually ran LEAN for once. I immediately knew that the crankcase was sucking in oil from the transmission. So I went out and got replacement seals for both the PTO and mag side of the crank, in with the new and out with the old, get it all back together and fill up all the fluids to take it out and finally get it jetted on the spot now that my issue has been resolved.

Well, so I thought.

Now it just runs worse than it ever has. Twice the smoke, terrible power, and a mid-range babble that will never clear no matter how hard you ride it. Jetting changes still have really no effect at all, and it's already fouled one plug in the short time I've ridden it since the seals have been replaced.

So what else could it be? Visually the transmission breather is not clogged with mud, so it can't be that. Is there any way to determine the leak without spliting the cases? :ride: :ride:

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Are you sure that you installed the seals correctly? The "flat" side of the seal, which is also the side that has the part number printed on, is the side that points away from the crank. PTO and mag get the same treatment.

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Yes. I figured if it was burning oil from the transmission, and I drained it out, leaving nothing to be sucked into the crankcase but air, it would create a very lean running condition... and it did, which confirmed my suspicion.

However, that only leaves the question of where it could be sucking the oil in now. I'm damn near positive that I installed them correctly, but I could always triple check, just to make sure they seated in there correctly as well.

I might also want to mention, I took the cheaper/faster alternative of getting the seals (didn't want to wait two weeks going through the dealer for them to come in) and got the seals at a bearing shop. for the PTO side (38-52-8) and the mag side (20-37-6) I had to go up a size in thickness because it's all they carried (So I installed a 38-52-9 and a 20-37-7.) I figured that if they were a little thicker (about 2mm each) it wouldn't make any difference, and the mechanic at the dealership agreed. I honestly don't see how, but could I have been wrong to have done this?

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The microfiche for 1993 shows Item# 14 as 36x52x7 and Item #15 as 20x37x6. I'm guessing the 36 is mm for inner diameter.

You mention putting in a 38x52. If so, and if that means 2mm larger, then that seal is probably not sealing on the crank correctly and letting tranny oil inside.

http://www.ronayers.com/fiche/300_0254/crankshaft_1993/crankshaft_1993.cfm?man=su&groupid=10840&parent=10640

Well, the thing is that my 93 RM250 is a very odd bike. I figured this out when I bought a boyesen reed cage for it that didn't fit (was too fat for the intake.) After calling up Boyesen and talking to one of guys about this, I learned that in 93, Suzuki decided to address some intake issues with the early model bottom-end of the RM250 about half way through the year that was robbing power. So my 93 actually has the bottom end that's found on a 94 model, which is why it only accepted a 94 reed cage, which was a little more narrow than the 93. This would also explain why the seals are that of a 94 model as well, so they're deffinitely the right size. :ride:

As for crankshaft play, I found none when I checked while replacing the seals.

Also, the seals that were in there were firmly in place with no visable signs of damage (I noticed that actually had been replaced before by a previous owner, but not sure when this was done.)

I also recently noticed an air leak when I made the mistake of trying to kick-start it with the exhaust plug in, however I couldn't pin-point the location of it. Sounds to be coming somewhere from the bottom end (not the sparkplug, cylinder and head are both torqued to spec with good gaskets) and it's a rather loud hiss, so deffinitely a vacuum leak somewhere. (but it might be the header o-ring not sealing, because it was leaking spooge in the past and quit doing it before I could replace it.)

Now, I haven't checked to make sure the seals are seated correctly, but what are the chances of having a bad main gasket between the cases? I don't think the cases have been split, but it's possible they had been by a previous owner in the past. That's really the only other thing that it could really be.

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