I just bought a 2000 yamaha blaster. It has all stock parts except bored 20 over with new piston and rings and has aftermarket reed valves (added before I bought it). It idles great. Has good low end power, but as soon as power band kicks in...instant burst of power, then it falls flat and engine blubbers and bogs. It happens everytime in every gear. I pulled the plug and its running way rich. I pulled the carb and it looks like new. Stock jets (230 main), stock needle settings. Pulled the reed valves....I think I found the problem. It has a 2 stage reed valve setup with stock reed cage. Both stages look like plastic. First stage are stuck open. Flipped em, still stuck open after tightening screws. Would this cause extreme rich fuel mixture and complete loss of engine power in mid-high rpm range? Has new air filter, has great compression, starts first kick, idles great, has good low end. Thanks you.

 

Sounds like the reeds are your prob, they definitly should not be stuck open like that.

 

Thats kinda what I thought. I have some new reed valves on the way, but it will be next week before I they get here.

 

I know it's been a while, but did the reed valves fix your problem? I am having the exact problem you had.