Yet another 8N backfire issue

[MingOK]

I rebuilt my 8N (12v Conversion) last year and it generally runs OK although is tricky to get the choke and throttle set to a point where it runs smooth. I get an occasional backfire through the exhaust and had a leaking exhaust gasket. I replaced the exhaust manifold gasket, cleaned the carb and set idle mixture and main jet at one turn out. I checked the plugs and found them very sooty as if its running rich but the backfire says running lean (?)

Is the front distributor/points my next check?

 

[mhb@ufe]

Back the main jet out one more turn. What are you running for spark plugs?

 

[used red MN]

I checked the plugs and found them very sooty as if its running rich but the backfire says running lean (?)

???

generally runs OK although is tricky to get the choke and throttle set to a point where it runs smooth.

???
I haven’t been around Ford tractors but I am sure this applies. The choke is basically only for starting. This time of year just about anywhere in the US (the OK in your username probably indicates the state of Oklahoma) you should only need to apply choke to start the tractor. Maybe possibly an occasional use in the first 3 minutes but once your past that point this time of year the choke should remain pushed in or “open” If you are using the choke “to make it run smoother” or whatever that is the reason your plugs are black and sooty. Black sooty “rich fouled” spark plugs can also be a cause for misfiring and back fires.

Is the front distributor/points my next check?

Points that are in a border line condition yet still run the tractor can cause a “low power” bad quality spark. This can also be a cause of back fires, especially with rich fouled spark plugs.

 

[Btzj02]

My Neighbor, an old school tractor mechanic used to tell me that if you are getting backfiring it is a timing issue. Many things affect the timing from installing the distributor incorrectly, points or firing order is not 1, 2, 4, 3, etc.

 

[Jim in LA]

It's easy to get 3&4 plug wires wrong if distracted or in a hurry.

 

[MingOK]

Back the main jet out one more turn. What are you running for spark plugs?

Autolite 85 plugs

I guess to help out the next guy, I'll tell on myself. The problem was the plug wires. I replaced them when I rebuilt the engine last winter but the wires to #1& #2 had cracks in them all the way to the wire. I replaced them and it runs fine now. I guess there's two reminders there:

1. Always check the simple stuff first.

2. Most aftermarket parts these days won't last nearly as long as original (yeah, Amazon, I'm talking about you).