Update: Went out and got a few new parts today. Started working on this last summer, and it looks like I didn't get all new parts for a "tune up."
I was able to rule out some stuff today, so that was good, but it's still not starting, but backfiring fairly regularly at #4 manifold. No where else.
Got cut-to-fit wire cored plug wires, a new NAPA distributor cap (BTW...it has a "1" on the #1 nipple), and AL 437 plugs.
Checked ohms across coil (3.0 ohms), which I understand from www.myfordtractor.com is w/in acceptable ranges. New NAPA coil this summer.
I verified #1 distributor nipple by feeling for the compression cycle on #1 cylinder, so that was nice to get nailed down.
I have never adjusted the timing in 10 yrs, so I left that alone.
Removed paper gas filter.
Added a couple gallons of fresh gas, to ensure sufficient gravity flow and fresh gas.
Fiddled with carb idle speed, idle mix, and main mix as per www.myfordtractor.com's carb adjust page. Along with Dell's advice, very helpful to have something written in detail to refer back to. At one point, I had both mixture screws maxed out for richness, which resulted in consistent backfiring.
-Plug wires are correctly hooked up on distributor cap.
-Coil is aok.
-Got a new batt and cables a while back.
-Nice strong spark, so I believe electrical is aok. (I asked for spark plug checker at NAPA dealer....head scratching time. They didn't have one.)
CARB: I tightened the idle handle. It was very loose. Put it on the anvil and carefully hammered the brass end to tighten up the connection. I double checked the float to 1/4". Verified that valve shuts off and goes on (put in water) Checked (again) that all orifices are clean using carb cleaner, wire and compressed air.
After cranking it some 10-15+ revolutions, I pulled plug #3. Bone dry. Repeatedly checked plugs. Dry. Pulled carb and felt inside wall of intake...some moisture.
So. I'm assuming the carb is "carbing," and there is sufficent suction (engine rebuilt 10-ish yrs ago before I bought it). Suction seemed healthy when I checked #1 compression cycle.
Since it only backfires at #4, a backfire in the manifold means a lean condition, the new plugs are dry after many revolutions, I'm concluding it's not getting any gas to the cylinders.
Could the manifold be blocked somehow, with #4 only partly open? Mice or wasp nests? I'll pull it tomorrow and see.
Thanks for any input.