I have an old John Deere 522 snow thrower that has a 5hp 4-stroke
engine. When I received it from my father-in-law, I noticed that it
occasionally had backfire (or afterfire) from the exhaust. But
lately, the problem seems to be more apparent -- either it happens
more often or I start paying more attention to this problem.

Seem like the backfire occurs as soon as I start the engine regardless
the engine is under load or not. Sometimes, I even see flame throwing
out from the exhaust. Consequently, the exhaust is blackened.

Online source says that the air/fuel mixture probably is too rich in
fuel and the incompletely burnt fuel ends up getting burnt in the
exhaust. According to the operator-manual, the problem must have
something to do with the carburetor not adjusted correctly or the
carburetor leaks air. Either case, the manual suggests me to bring it
to the dealer. But I really don't want to bring it to the dealer in
the middle of winter when I need to use the snow thrower. I would
much prefer to bring it in in late winter or spring when I don't need
to use it any more.

My questions a

o Can I continue using the snow thrower in this winter? Then I can
bring it to the dealer in the spring.

o Is this something that I can fix if I can find a service-manual and
a parts list? I am reasonably handy (home improvement...etc) despite
the fact that I have never opened up an engine before. Note that the
operator-manual doesn't say anything about fixing / checking /
adjusting the carburetor. I hope that the service manual may have the
necessary info.

Thanks in advance for any info.

Jay Chan