timing or distributor question

Machine249 · May 29, 2010

I have a F504 gas that I"ve been trying to get timed properly. Right now it will back fire after shuting the engine down. The distributor thats on there now is not original, it has the same part number as the H and others. The manual I have gives the timing curve for specifically marked distributors. Should I get the correct distributor or go with the one I have? If I keep the current one how should I set the timing? Thanks in advance.

gene bender · May 30, 2010

That is not a timing thing but usually a spark plug thing. Just kill the engine in gear. The timing is ok or it wouldnt even start and run. The curve you mention is not important as those engines would run with a magneto and there was no curve.

Jg20601 · May 30, 2010

I agree. If the timing was off- it would not be running. What I would d is paint a mark or put two punch marks for future reference. And put a timing light on it to note the timing.

The AC Model B my father had used a distributor salvaged from a wrecked 4 cylinder chevy when the magneto died and the previous owner couldnt get one. Ran great though.

John T · May 30, 2010

You begin by setting the static start timing so she will start, which is pretty close to fire right at or near TDC, and then the distributors spark advance mechanism (mostly centrifugal) determies tha advance versus RPM to match the engine and its compression etc.

Timing specs for distributors often say set it for x advance at x RPM and you can do that with a timing light butttttttttt remember when youre rotating that distributor youre ALSO affecting the static start timing.

If I have no manuals (the usual case lol) I set the initial static start timing first by getting the No 1 piston to TDC and adjusting the distributior so right there she fires. Then she should start and use a light to see where she fires as RPM is advanced and if its close I let her go or perhaps tweak it a bit but not so much the start timing is way slow or fast. It also depends on if its a hand crank or an electric start, the hand crank isnt very forgiving, one dont like kickback from too fast timing while too slow makes them hard to start. An elec start is more forgiving up to a point.

Thats all I have to say about that for now

John T

Machine249 · May 30, 2010

Thanks for the great info guys. I would be lost without you guys here. Thanks again.

Owen Aaland · May 31, 2010

The electric shut off solenoid on the carburetor main jet was developed to correct this problem. Without a positive fuel shut off in the carburetor fuel continues to be drawn into the engine as it spins down after the ignition is turned off. Hot spark plugs will cause the engine to continue to run . The backfire is caused by fuel passing through the engine and entering the muffler where it ignites. Letting the engine cool down a couple of minutes before you turn it off can help eliminate the problem

timing or distributor question

Machine249

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gene bender

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Jg20601

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John T

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Machine249

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Owen Aaland

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