|JON, (re jetting for a 1996 Gas Gas 370)
I live in Victoria,B.C. ,on Vancouver Island . My riding conditions are: temperature ranges from -2 to 15 degrees celcius, wet and muddy in the winter, dry and dusty in the spring/summer. The humidity today is 93% . We generaly ride very tight trails with lots of hills and rocks that we ride up. I normally ride in 3rd gear with alot of idle to half throttle use. The bike always gets a good full throttle clean out at the end of our rides. I run Chevron 94 octane fuel with opti oil (100-1) I still don't feel comfortable at that oil ratio ! I hope this is enough info if not e mail me if you need more.
Jim Snell of Rising Sun Imports has given me some updated info on jetting the 96' 370 (338cc's) for at, or near, sea level. This should give you a very good place to start.
Main: 115 (stock)
Pilot: 45 (.020" drill)(stock is 38)
Needle jet: 266EM (stock)
Needle: X18 @ 3rd clip down (stock is X19)
Airscrew: 1.5 turns out (stock is 1/2 turn out)
Use Hi-octane pump gas (or a combination of race/pump gas) of 95 to 100 octane (don't go over 100 octane and avoid Ethanol blends) and 80:1 on the premix ratio. The pilot change is mandatory and will make a big difference in performance. Jim also pointed out an issue that may need further clarification on my part. Gas-Gas recommends 95 octane fuel in their engines. I try to get my fuel in the 98 to 100 octane range just to be safe. Running octane much above that will usually not give you better performance and very high octane will often decrease performance unless you modify the engine. Contrary to all the T.V. ads in the U.S., more is not always better.
Again, my thanks to Jim.