Thread: back fire ford flathead

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Well I really don't know but I'll keep your thread going until Richard-Tech1 or Bob Parmenter gets back to you. Unless your block has been rodded with adjustable lifters you can rule out adjusting the valves since they are ground in at the factory. Also I don't know whether you have a '36 distributor or a later model. It basically sounds like a timing problem so try using a timing light and check the static advance and also check to see if the automatic advance works. My V8 book says the inititial advance should be 4 degrees with an automatic additional advance of 16 degrees (crankshaft) between 400-3000 rpm and the stock setting for the spark plug gap should be only 0.014"-0.016". Thats assuming you have a stock distributor. If it runs well at low rpm and backfires at higher rpm maybe the advance is not working? Back when I was fooling around with flatheads I used the system of replacing parts until it got better and I recall that a rebuilt distributor and a new or rebuilt carbuerator with new plugs really made a difference, but today the parts are harder to find so you have to pinpoint the problem(s). The stock '34 distributor had more total advance of 4 + 22 degrees at 3000 rpm so maybe you have an earlier distributor rather than a later one? Maybe you have too much advance? I don't know but there were several types of distributors as well as carbs so you need to identify them before you can get the right settings. In this day and age it would not be unusual for such an older engine to have "any parts that fit" from various years. Lost in the modern SBC-350 plain vanilla track is the fact that there used to be the magic numbers "Ford '32-'48" with almost complete interchageability and believe me a whole lot of swapping occurred!

Don Shillady
Retired SCientist/teen rodder