As soon as I get a chance I'm going to take the bike to a TY guru here locally and see what he thinks.  Maybe I can ride one of his TY 250's and see if it does the same thing.  

Yeah, it's worth it - one of the most knowledgeable engine guys I knew heard my TY at a trial and told me what was wrong, lol

I hope he can tell me one way or the other.  I only have the one bike and nobody around me has another one that runs, so it is hard to tell if it's normal or it could be much improved.  

So today I changed the main jet down to a 112 and re- peaked the idle air bleed screw.  I think it's running better now, but still going to see the guru tomorrow. 

I keep finding dust/dirt or sawdust in the float bowl drain plug.  This can't be a good thing or normal.  The fuel filter is inline, but is not stopping this contamination.  I guess I'll have to investigate the main tank and it's filter, the fuel source container and the whole picture. 

 

Took the tank off and cleaned it and the fuel petcock. drained the mix and filtered it thru coffee filters- not much dirt or debris in the tank.  The fuel filter is one of those very small clear cone shaped types and it did show about 10% of the surface area having something stuck in it.  The flow arrow was correct.  

Question- if there is debris in the float bowl drain plug recess, is that strong evidence that the contamination is from the fuel itself, or is it still possible that there is some problem with the air filter?

 

 

What kind of debris?

 

It's possible the fuel filter mesh is too large to pick up on something floating in the fuel, or that the fuel mix has been sitting long enough to separate, or even that something inside the system is breaking down (ie. very old air filters can turn to dust, something in the carb can be scraping when the throttles applied, etc).

The fuel I use is fairly fresh about 2 weeks old, but the plastic jugs I put it in may have gotten saw dust in one of them at some point in the past because I use the same mixture for the chain saw, and that jug is probably pretty dusty.  The gas tank on the bike has fairly fine screens in it and they are clean and intact, so I just filtered the same fuel thru two coffee filters and put it back in the rinsed out fuel tank.

I think I will put in another new air filter and get the proper air filter oil this time that is made for the air filter brand I'm using.   

Since I didn't find anything in the fuel tank to speak of its hard to say whether the culprit is airborne or from a dirty fuel jug.  There was the usual dust around the fuel tank cap gasket, but nothing like that was in the carb float bowl drain plug recess.  It looked more like sawdust if I had to make a guess. 

Yeah, dust like you get around a chainsaw can be fine enough to swim past a non-paper filter, I have to watch for that too (and limestone dust from where my garage floor is breaking up in places)