OC3 shuts down

[triedntrue]

Hello - New to the board with an old problem.  My 1955 OC3 starts on first crank, runs great for a half hour, then starts to miss and shuts down.  I have to let it sit for a while before it'll start again, and it does start right up.  I've replaced the coil twice, new points, new condenser, with no luck.  Have read of many other OC3s with the same problem but never how they made out - problem resolved?  Any advice?  Thanks.

[Blake Malkamaki]

Are you sure the problem is spark? Does it have spark immediately after it quits? Is the vent in the gas cap unobstructed?

[Jack in NB]

See if applying choke smooths it out a bit when the spitting starts. This would signal a fuel flow restriction, like the plugged cap vent, or in the plumbing.

The note that it takes a while to quit suggests the plugged vent. In that case it would take less time to quit with a full tank, quite a bit longer if the tank is near empty. You might be able to hear a hissing when loosening the cap just after it quits, as the air rushes in to neutralize the vacuum.

I had a similar problem a few years back, and it turned out to be debris plugging the top fitting on the sediment bowl, in the stem going up into the tank.

There is a 1/8" thread pipe plug on the bottom of my carb. Removing this should give you a healthy flow of fuel, continuing for some time after the carb chamber drains.

If your carb doesn't have a drain plug or you can't loosen it, it's almost as good a check to loosen the fuel line to the carb. This won't wring out a carb problem like a sticking float, however.

Try to capture the fuel for environmental (and financial!) reasons (it's awkward!) and for God's sake, don't try to start the tractor for several hours, to let the fuel spilled on the mag cap dry off completely. You don't want to create a July 1 (CDN)/July 4 (USA) fireworks display with the old girl!

[triedntrue]

Will check the fuel issue and look for spark after it quits and let you know how I make out.  Thanks very much.

[triedntrue]

Followed up on your advice and turns out that I also had debris plugging the top fitting on the sediment bowl, in the stem going up into the tank.
Only took 20 years to finally figure it out!  Thanks for the help.