SP100 (oi) lack of power

[vfriese]

Just reassembled my 100SP that I cleaned up and am attempting to bring back to life.  It just will not run right.  It starts great and revs ok in neutral but when I put it on the road it just won't rev like it did when it was younger(just like me).  Anyhow it seems that when I last had it running (about 20 years ago) it would really get going and pull like crazy after you got it off idle a ways.  I have disassembled and cleaned the carb, gas is good, new petcock, etc.  Could it be the rotary valve seal?  What would indicate a problem with this?

[OldSwartout]

Confirm that the throttle is lifting the carb slide all the way. If so, then check the exhaust baffle, then the exhaust port for carbon buildup (or mouse nests or insects in the exhaust).

I assume you had the air cleaner apart already.  Mice really like airboxes.

[vfriese]

I have the side cover off.  I have had this thing down to the last bolt.  Except for dismantling the engine.  The silencer is out. If I run it without the muffler it sounds great but you need that for an expansion chamber (I think). I am really curious what the indications are if the rotary valve seal is bad?

[OldSwartout]

If the rotary valve seal is bad, the engine will pull in extra air (through the transmission, from the transmission vent), which would make it lean. That might make it not want to run well at higher RPM if it is really lean, otherwise it would likely make it run better (up until it seized). It will also pull in oil from the transmission, which will make it smoke significantly more that normal, especially if it is bad enough to affect the running at higher RPM. Just a slight leak at the seal would just make it difficult to start and idle and smoke a little extra, not affect higher RPM.

You do need the exhaust system to make it run right, having the baffle out might make it run a little better, but will also lean it down just a bit.

It does sound like you would have caught nearly anything I can think of external to the engine.

This could be an embarrassing question, but how much different is your weight now than 20 years ago? A 100 will perform  much differently with a skinny 16 year old than with a normal 40 year old.

[vfriese]

Hey, I'm over 60!!!!! Had this bike since new.  Cost $425.  Anyhow I have been running it with the r hand cover off, just to watch things.  Sucking in raw air(a bit dangerous for the engine I suppose).  It won't pull 4th gear.  I'm 200 lbs., and I'm sure that's not the deal. At 14 with a girl on the back we would have been heavier than I am now! The power is less as I get into mid range.  Interestingly I have found a clear/brown type oil in the case under where the oil pump would be if I had the pump in there.  This has got to be transmission oil as you mentioned.  How difficult is it to get to the rotary seal to take a look/see?
Oh, by the way, thanks for your response

[OldSwartout]

If it won't pull 4th, then there definitely is a problem. You just need to remove the carburetor and the clutch cover to get to the rotary valve. I'm not certain on that bike; you may need to move the brake lever and/or footpeg and bracket to get the cover off. Someone else more familiar with the 100s can chime in here.

You might want to check compression too. Not pulling 4th and lack of oomph as you're running up through the RPM range could be worn or stuck rings or the previously mentioned exhaust restriction (which you've verified doesn't exist).