exhaust backfires

**james n** · 05-05-2009, 12:06 AM

I have a boxxer 421 starts fine runs fine idles fine cleans fine just when i am done with a job and remove the vacuum hose for the machine it starts to pop and backfire recently changed fuel filter and plugs please help have a lot of work cant afford for the machine to be out service Did replace broke idle cord could that be it to high rpm?

**able 1** · 05-05-2009, 01:59 AM

Hows the air filter? Mine will diesel when I need a new one.. Never had it pop on me though.

**Ara Klujian** · 05-05-2009, 02:10 AM

Did you change the plugs before or after this backfire problem? If before you could have the wrong heat range spark plug.
Other reasons for backfire will be:
Excessively rich or lean mixture
Overheating
Excessive carbon buildup
Hot valves or burned valves not seating properly
Incorrect timing or cracked distributor cap.
Hope this helps.

**Graystar** · 06-26-2011, 02:58 AM

I had this problem today....backfiring through the carb though, from out of the blue....I barely got the job done...very embarassing seemly fixed it by screwing in the air mixture screw a bit....whew!....I was worried....also, it was throwing out black soot out of the exausht a short while ago got it all over my white shorts and hands etc....also embarassing....and this was a clogged air cleaner...easy things to fix but oh so important and can lead one to imagine the worst!