Miscellaneous > The Sallyport

Engine backfiring through carburetor

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Sir William:
Check the overall condition as well as the gapping of your spark plugs- if you notice any blackness it could mean carbon fouling, may be time to change them.  As its a 73 (nice year by the way), I'd do the wires and distributor cap & rotor as well.  All it takes is one cylinder to act up and you're running rough.

I should've read through all of the responses first.  D'oh!

Mike W.:
When I get a chance, I'll check down the carb throat while revving the engine to make sure there's no clogs in the jets. Other people online are suggesting a bad vacuum diaphragm, bad condenser, or even a bad dwell angle. I'm more certain it's a lean fuel-air mixture than it is an ignition problem. I'd bet heavily the problem lies in the carburetor or the intake manifold.

Mike W.:

--- Quote from: Sir Edward on 2015-03-16, 13:45:37 ---
Maybe the fuel mixture needs to be a little more lean? I'm totally not an expert, but backfiring sounds like you're not getting complete combustion in the cylinders.

--- End quote ---

Ed,

Backfiring through the carb is most certainly the result of a lean mixture rather than a rich one. The fuel, being too rich in air, is not as flammable. Unburnt fuel will start to accumulate inside the combustion cylinder until there is enough that it is finally ignited. A lean mixture is slow-burning. The fuel will still be burning as the intake valve opens to let in the next round of gas. That incoming gas is then ignited prematurely and the explosive force comes out the carburetor.

Generally a rich mixture causes afterfire.

Sir Wolf:
HAH! a kid after my own heart.  I bought a 73 cougar (sister to the mustang) when i was 15. had it till i was in my 20s.

Sir William:
One of my college buddies had a 69 Cougar...I don't know why, but I liked it better than its sister.  Dad had a 71 Mach One with the 351 Cleveland...that was a monster, my favorite of all Mustangs.  Although the newest one is certainly eye-catching.

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