Update--Thanks again for your help lads-- I found an old pilot jet in my tool box so I drilled it out...just for the hell of it..
It really solved the problem-- made the power meaty at the bottom end.
Instead of just messing around, practicing on a very,very small rocky section I took Cherie ( I name all my Shercos)to a bona fide trial last sunday ( It's been 10 months since I rode an event) .
I think the longer run out has cleared out the exhaust.
The softer power delivery made the bike grip on mud and roots much better than the 250 ever did-- now I get it (the need for the spacer).
Cheers