Just thought I would share this with everyone as maybe somebody else has had the same dilemma. The '37 engine has been bored and sleeved back to original specs, the carb has been professionally rebuilt, and the Mag is a new, rebuilt Wico X with lots of spark. This tractor will start every time on the second compression when cold with the choke set at about 3/4, throttle set at about high idle. Runs great, idles great, doesn't foul the plugs. But if you shut her off and wait an hour or so, she just refuses to start, choke or no choke. I finally figured out that this particular engine likes to start with choke when cold, but when warm she only will start with the throttle set back to almost idle. No choke and just a tiny bit of throttle and she starts on the first compression. Took me a year to finally figure this procedure out. I guess these old engines all have a certain way they like to be set up for starting. Are we getting more fuel into the cylinders with the throttle closed? Less air=more fuel? Like to hear the experts comments.