92 rm125 running rich

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#1
I'm a little bit puzzled with the tune on my bike. Running extremely rich at 50-100% throttle. Should be a main jet concern I assume. Idles fine with a stock pilot jet and air screw at stock position. It's a freshly rebuilt bottom and supposedly has about three hours on it. Fresh plug, pro circuit pipe and moose filter. I figured with a stock 172 main jet it would run lean with the mods. It currently has a 160 and is still running extremely rich. Also running 40:1 on my fuel mix. I haven't messed with the jetting yet but wondering if I should be looking for anything else before I start.
 
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#2
How are you determining that the jetting is rich from half to full throttle?
 
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#3
Lack of power and a LOT of smoke. A lot more than it should. I can run it at idle or quarter throttle for about 30 minutes and the plug comes out clean. Get on it for about 5 minutes and it'll bog down til the plug gets coated in oil. Only did that once with the new plug.
 
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#5
What you are describing sounds like a leaky crank seal on the right hand side of the crank. It sounds like it's pulling in oil from the gearbox and burning it. A leaky head gasket can have similar symptoms. Is the smoke white (most likely coolant) or blueish(likely gear oil) ?
 
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#7
That would be the logical place to start. Look for damage on the crank end where the seal lip rides. If the crank is worn in that area a new seal can't cure it.
 
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#8
I'll do a thorough inspection before I put it back together. I'm used to car engines so this is a whole new world for me.
 
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#9
If you are comfortable with auto engines then this will be a breeze for you. The same basic rules apply, the details are just a little different. Think of this like the timing cover front seal on a V8. The approach to getting a good oil tight seal is the same.
 
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#10
Yeah, I've done plenty of rear main seals on automotive engines. Knicks on the crank can cause big sealing issues. I appreciate the input. I'll try and get it pulled apart tonight and see what's going on.
 
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