I have a 1987 Mazda b2200 truck 4 cyl 2.2 5 speed.It recently started
backfiring
Thur the exhaust.I read that it could be a few things but did a search
of and
found that it could be a few things.1. dash pot found it on carburetor
seems to
push in  and pop out OK read that it should push in slowly and pop out
quickly
seems to do just that.2.Timing I don't have a timing light but I did
adjust the
timing I marked the timing for reference then advanced and retarded
timing test drove
didn't stop the backfire problem reset to original position.3.I took
out PVC
valve and shook it sounds OK but don't know how accurate that test was
either
way it was on the list of possibilities but was a unlikely one.4. the
exhaust
is broken back by the front of the muffler could this cause this
problem or was
it a result of problem?5.Looked over vacuum lines seem to be OK
there's lots of
them but didn't see any obvious leaks.This truck runs pretty good
otherwise but
when I back off the gas it backfires threw the exhaust more so at hi
speeds
around 60 but at low speeds also at times.Any Ideas common problem
with these
?Thanks in Advance