1931 ford model A back firing ?

[cyrus]

HI forks, I have a 31 model a and had to replace the original carb. I installed a glass fuel bowl and a new carb and lines. She starts right up, idles fine but seams to have lost some power and between shifts she back fires. Not a lot but it does. I removed the throttle linkage and retarded it to set Idell then turned out the idell screw 1-1/2. I dont get it. It didn't black fire and had more power with the old carb.

The old carb had a crack in the upper body near the screw hole for the sediment bowl.

thanks Jim Brennan

[Harold Phillips]

One cause of backfire can be a lean mixture, the adj. screw is for low speed mixture normally. I would check float level as a start. do not have a Ford so am not up on there carbs. but am going on a hunch.

[old car fan]

i posted on the other forum you posted, Harold is right, to lean,i think

[Siegfried]

I rebuilt a few model A and flat head V-8 Ford carbs for the AACA Museum. While testing out my work cruising on the museum grounds I encountered the same problem. Backfiring between shifts, and discovered, by trial and error, that enriching the mixture solved the problem. Amazingly an early Ford carb is as simple to rebuild, and adjust as is an air-cooled pre-1971 Volkswagen carb.

[rons49]

Cyrus, do as the earlier responders state. What position is the spark lever when the backfire occurs? Remove the fuel cap and just lay it on loosely. If you open the choke valve 1/4 or more does the back fire still remain? I will assume that the points and timing are set to standard. Do you have an indented firewall (late 31)? I presume not and a fuel flow restriction could be occuring at the firewall bowl filter or filter screen in the carb base. fuel cap Check float level. Check manifold gaskets. Spray some wd-40 liberally around the mating surface of the intake & exhaust manifold with the engine running. Listen for idle changes. Check gasket surface of the carburetor. Air could get in that way also. I had a similar case in my 31 years ago gasket bolts just a tad loose. Backfire can occur do to a overrich mixture also, by unburned fuel blowing off in the exhaust.

[cyrus]

Thanks for your help. I have replaced exhaust and intact gaskets. (but haven't tried wd40). I have real good gas flow new gas bowl and filter. I installed new plugs,wires,cap, dist. body. rotor and cap. Ha vent timed it yet or replaced points. It dident back fire until i ran out of gas and after cleaning out the old carb and lines discovered their was a crack in the old carb housing. So i got a new style rebuilt. I haven't check flout height i dident think i had to. Back fire (not a big one ) but u can hear it happens between shifts and with advance lever half way

thanks Jim

[MCHinson]

I also posted this in the other discussion of this same topic, but just in case you see it here first...

Try cracking the Gas Adjusting Valve open about a quarter of a turn. If the carb jets are correctly sized, most Model A's like about a quarter of a turn open or so on the GAV. When you change carbs, you have to try different GAV settings as the jets in different carburetors are usually slightly different.