Backfiring Issue

[Guest philedmonds]

What would cause my '49 B1FA to backfire? The carb has been rebuilt, I have a new fuel pump, new fuel filters, new hoses, a clean gas tank, new fuel and I've turned the idle screw almost all the way closed. I'm still working on the timing (other posts) and may have it off by 10 or 20 degrees at idle. I've not run the engine at speed much yet and it seemed to be OK then, though. Any suggestions are much appreciated. Thanks.

[greg g]

Probaly related ot your timing issue. Is it popping through the carb or blasting through the exhaust. You may also have a valve or two not sealing completely. Have you done a recent compression test???

[TodFitch]

If it is "blasting through the exhaust", check for leaks on your exhaust system, especially on your exhaust manifold. This will cause "backfire" when decelerating and/or running down a grade on engine compression.

[Guest philedmonds]

Most of the backfiring is through the muffler. I had planned to work on the engine today, but I worked all day reinstalling door windows and run channels and still didn't finish. I had thought about doing both a compression and a leakdown test and will try in the next couple of days. I'll try to get the points set properly and the timing and then see what happens. Thanks.

[grey beard]

Phil,

Many people do not realize that when you set timing on MoPar flatties, there are TWO adjustments that can be made - one on the slot in the distributor at about 8 o'clock and the second on the bottom of the distributor, which is sorta' hard to see. Might need a mirror.

Here's what I just had to do to get my own B1B running and timed correctly. First, bump the engine over slowly with the starter until your TDC mark comes up to the pointer. Make sure your distriburor rotor is pointing exactly toward the number one plug wire - should be at or about the 7'oclock position on the cap. If it is half a turn off, bump the engine around again till it's right on the mark.

Now, with the engine at TDC, study the distributor rotor position. It MUST be just about exactly on the money at this point in time - pointing toward the number one plug wire on the cap. Loosen both adjustments as described above and move the dist around untill you are satisfied it is as close as you can get it.

Now snug both adjustments down and hook up your timing light. Get it running and at or near a slow idle. You cannot set initial timing until the engine idles. If you try to do this, the centrifugal advance will give you a false reading. My oiwn engine ran fine before I overhauled it, yet when I started it up now with the same dist. I had o move bottom dist adjustment quite a bit to get it in time. Someone had moved this in the past to compensate for the worn timing chain.

Now move your distributor to get the timing mark just a little toward the steering box from TDC. Lock the timing adjustment on the distributor down, and at this point adjust your carb idle speed and mixture screws. If it backfires now, you likely have a timing chain/gear issue. JMHO

Worked for me. Runs fine now. Hope his helps.

[Guest philedmonds]

Thanks for the info. I think I am OK now - see other post. I'll print this and file it in my manual.