Backfiring Only in 5th gear i give it gas then it boggs down a little and backfires.

SOURCE: engine kiking and bucking and backfireing

1. The jets in the carb need cleaning,
2. You should Also clean or replace the spark plug,and air filter
3. Have the timing checked

SOURCE: Backfiring when idling back down thru the gears

that seems to be what they do, i too have a 650a and have jardines on with baffles, it still pops and cackles when you roll off the gas. are you running no baffels? when i took mine out i noticed a drop in power as i had removed the requierd back pressure for optimum performance. you can get small baffles to slip into straight pipes from jc whitney for about $5 each.
anyway back to the backfire. my local bike shop shrugged their sholders when i asked them about mine saying it's what they do. you will get used to it and you will find a way to kinda not make it do it so much. i actually have grown to like it now, except when there are cops about.

happy safe riding

SOURCE: yz450 f stalls when you hit gas hard

it sounds like your main jet needs to be rejetted and tuned in it is sending to much gas and stalling out the bike

SOURCE: yamaha warrior atv [yfm 350] bogging problem

Try checking the switch for your parking brake. It is the top wire in the clutch handle boot. This wire connects to your CDI box, and restricts the RPM's while the parking brake is engauged. To find out for sure, trace the wire down to the plug under the headlight assembly and disconnect it. Now try starting you machine and give it some throttle!

SOURCE: yamaha blaster 240cc

the mechanic should adjust the idle of the fuel pump because.I think there are much gas that is going to the engine.and also check the air filter if there are dirt on the filter then replace filter .for sometimes it can be the exhaust.