Backfiring

jrcotner · Post by **jrcotner** » Thu Feb 18, 2010 2:52 pm

All of a sudden I've been getting backfiring through the exhaust and air cleaner on my 1971 710M. It even dislodged the air cleaner cover. I haven't done anything to the motor, and am using the same gas. Any ideas on where to begin the search for causes?

Thanks,

John Cotner
Falmouth, VA

andy · Post by **andy** » Thu Feb 18, 2010 3:53 pm

Check everything from the exhaust manifold back to and through your muffler.

Had a similar thing awile back and had it answered here and sure enough the problem was the muffler and the couplings to the heat exchanger and the muffler. Do not just have someone weld them to make it past inspection, this will only lead to other problems. Don't ask me how I know this, because it will cost you half of what I had to pay to fix it, to find out.

Andy

pcolette · Post by **pcolette** » Thu Feb 18, 2010 4:08 pm

I had this problem Winter 2008-9 when the air filter partially froze up and restricted air flow. Very cold but damp days can make the metal parts of the filter ice over. If the filter is already marginally ready for replacement, it's even more likely to happen.

Just one of many possibilities.

Paul

chacaocop1 · Post by **chacaocop1** » Thu Feb 18, 2010 7:49 pm

Check the screw that holds the distributor in place. At one time my 712 was doing the same and the distributor screw was loose and the timing was off.

One of the many possibilities...

Erik712m · Post by **Erik712m** » Thu Feb 18, 2010 8:14 pm

Sense it's out of the carbs and Exhaust I'd go with timing or loose carbs.

My experience with popping out just the carbs has been because of the lack of air flow but it never popped out the tail. When I lost a bolt out the tail pipe it popped out the exhaust but not the carbs.

undysworld · Post by **undysworld** » Fri Feb 19, 2010 8:36 am

I agree w/ Eric & Chacao.

I've had the air filter freeze, it gave me tons of oil smoke out the tail pipe.

I've had leaks in my exhaust, it gave me backfires but only out the tail pipe.

Jerbearyukon · Post by **Jerbearyukon** » Mon Feb 22, 2010 11:49 pm

Well I had that today along with her not starting.

So I went and got a new gas filter and airfilter (thought it might be plugged, but it hasn't been replaced ever so I thought what the heck).

Got new plugs and went home to see if I could get her running.

So I tore the cover off took out the air filter and the housing. The air filter looked ok (the NAPA store didn't have one but will by friday).

Noticed there was OIL in the housing. I remembered that happening when I bought her and traveling through Kansas to Dennis's shop in Denver. He told me to take out the filter until i got there (there was black smoke and backfiring then too).

So I tried to start her.....backfiring out of the carbs fire the works WOW what a show, but she started. I reved her up some and it finally had her running smooth again. So I replaced the gas filter anyway...cleaned the housing of all the oil and she is running like a dream again.

Who da thunk it....something so simple as the air filter.

More i know the more I know i don't know.

Jer bear