haven't read all answers--later--but think you said tried a carb off another that doesn't blubber but still does on this bike. Story--bucket racer TF100 [laugh now if you want]. Had a yamaha reed block welded into the inlet & blubbered at about 1/4 throttle & was just as it came on the pipe. Needed full throttle & clutching to get over it then away [hanging off the back--almost!!], was carburation rich type simptons but couldn't lean it out of it without stuffing it to the point of gasping but not fixing it. Soooo--some smarty said reed flutter--in conjunction with overporting causing reed flutter as the power came full on type thing--said double the reeds for a try!!. So doubled them--just ordinary RT2-360 steel reeds & reed block--anyway, it fixed it 100%, couldn't believe it. Never too old to learn--when you think you know everything lol. Was just a thought. If rich at idle though & won't respond to jets or mixture screw it 'does' sound like needle jet & needle combo i must admit. Choke not failing to close off. Bit of stray filter sponge in the airway to the needle jet [emulsion tube] in the mouth of the carb. etc etc. Cheers.
