Got an old Subaru GL Hatchback 4wd, 4spd, 2.7,or 2.9 4 cyl. Carberator, 180,000 mi, Made october 1985. It keeps backfiring, usually when your shifting gears, and not really when the rpm's are high. If you rev it up and down, around 2500-3000 rpm's it lets out a KA-POW!!! Kinda like sanford and son. It has an anti-backfire valve, and its been changed, so has the plugs, and wires but still no help. Does anyone have any ideas? I have no clue whats goin on.
Pump it a few times like most carberated vehicles and 5-10 sec it fires up, rev it up a few times and it will idle on its own. Idles a lil ruff, and sometimes the idle will go up faster on its on, tap the throttle and it will idle back down.
As far as i know backfire could be caused by rich conditions where unspent fuel is getting into the exhaust building. Not a normal condition but could easily address. Just replace the whole carburetor or the stuff intact on it and the problem would be solved.