The old gas had been siphoned out and a full tank of new gas put in. But I'm guessing that either the carb had old gum in it, or perhaps there was enough antique gas still in the tank to cause problems when mixed with the new. It has a Grose ball/seat seal in it, which seems to work well. The ball had stuck in the seat. Odd thing is that it didn't stick closed until driven about 90 miles.

We took the carburetor apart and gave it a good cleaning.

Driven about 100 miles since then and hasn't stuck again.

Yep, going to adjust the valves next time it's warmed up.

You can use the timing light to set the timing so that the ball is just at the edge of the window rather than in the center under the marker.

Does this engine not use an oil slinger in the rear instead of a seal? My understanding is that if you build pressure with a drill, oil will run out the rear because the crankshaft isn't moving.

Yep, it has a slinger, not an oil seal on the rear main. Not sure about about bulding pressure with the drill (we didn't do that), but it is leaking like the Exxon Valdez out the rear main. Not sure what I did wrong--the little ball in the rear main was free and the bearing is plenty tight.

About 1/2 quart of oil has leaked out from there and other places in 200 miles (the pushrod cover is leaking along the bottom-tightened the screws some more so will if that fixes anything)and oddly some oil around the fuel pump where it bolts to the block. Brand new gasket and bolts are tight, so another mystery.