I am working on a trailboss 250 r/es for a friend and have ran into a stumper. The bike is a 85-88 model, it has 120 psi of compression and holds it pretty long so i know the seals appear good in the bottom end. It has 2 gallons of new premium gas in tank and good on oil and a brand new plug i got at the dealer. my problem is that it will only run on ether and not the gas  and it seems to crank along time to start and run at all. Any info?  

Try adjusting the valves. If they are out of adjustment, it will have trouble starting and won't run worth a crap. The ether is more flammable, and is probably barely burning. I had the same problem w/ my Raptor 660, but after adjusting the valves, it starts on the first or second turn even when cold.