[ENTDOC]

I would look into 40mm venturies at some point but for now I then to think your mains are too small, so I would go up to 165 and also raise you air correctors to 200 or so(they should not affect 2500 stumble but may help keep top end good. Since your problem is at the transition point you have to consider different emulsion tubes also but go with the simple and cheaper thing first. Do you have 2 or 3 progression holes? If 3, drop your idle jet to 170, if 2 stay where you are. Make sure plugs are ok and carbs are balanced. I always start with new plugs when making changes.