MTFCA Forum

What makes a model t engine backfire going down hill. The throttle is all the way up. Is it carburetor or timing?
Dennis K Anderson
Maryville Tn

Running very lean under those conditions. My Austin Healey would do that too, when downshifting. Never done that in the T.

Dennis,

I am not a mechanic just a parts changer. If you are referring to that beautiful Postal Truck you built I think the issue may be a loose nut behind the wheel buddy. Seroiusly, call me, I have a spare rebuilt carb you can borrow to see if yours needs to be rebuilt.

May best to Ms. Connie,

Dom

If the spark is retarded going downhill, the spark will come late, causing some of the fuel to ignite in the manifold or muffler.
Norm

Dennis- I'll bet that you are not running a standard Model T muffler. I'm running a muffler for an 8N tractor on most of my T's and they all backfire going downhill, but only if the timing is retarded. They are tough mufflers- much tougher than the Ford take-apart mufflers that are destroyed by a backfire.
When my granddaughter was young we'd be on a tour and I'd make the car backfire and she be in the back seat yelling "do it again, Poppy!"
Cows on the roadside hate it.

Describe what you mean by "backfire". Do you mean explosions in the muffler, or "popping back" out of the carburetor? Each has a different cause.

The backfiring is in the muffler. I am running one of those stainless steel mufflers. I don't think it will burst apart, but popping like that can't be too safe. Your commits are helpful and I will continue to chase this problem. Dom, I have been looking for that loose nut behind the wheel for a long time. Can't seem to find it. Thanks.
Dennis K Anderson
Maryville Tn

What Mr. Kling said.