Re: backfiring T3

[Theo Thepen <thepen@pi.net>]

I agree with Al. It's mostly caused by air that gets in the system
through a leak and basically adds extra oxygen to the unburned (rich)
mixture that went straight through the cylinders and makes it 'explode'
in the exhaust. That's why it only happens when you let go of the
throttle at higher revs, meaning high vacuum and rich mixture. Modern
cars and also motorbikes have a system with valves in the carb or FI 
system that corrects the underpressure in such situations and prevent a 
rich mixture and thus potential backfire. I don't like it on a bike so I 
removed it from mine. I think a mild backfire is one of the charms of a 
big bike.
The options the others mentioned, esp. the tuning, should also be checked 
of course.
Cheers,
Theo