1937 John Deere A runs erratically

[dlbuck]

I was driving my A down the road, it was like someone through a switch and it started to run with a repetitive miss. I had the mag
rebuilt, new wires, plugs and went through carb. It will start but will still miss and backfire through the carb and the spark plugs
will be black with soot. Any advice will be greatly appreciated. Thanks.

 

[Paul from MI]

Look for a sticking valve.

 

[dlbuck]

I was thinking that would be my next step, but thought I would ask first with people that have more knowledge than me.

 

[Loosehandle]

Did they replace coil in mag?

 

[dlbuck]

Yes, it was a total rebuild.

 

[dlbuck]

Found the problem, the tappet adjusting screw broke off the rocker arm.