Try this when you go to restart after running it for awhile.
1) While cranking, slowly depress the throttle all the way to the floor.
2) IF it doesn't start after 3 or 4 times as it turns over,
3) slowly let the throttle pedal up while still cranking.
If it catches and starts try to remember what position the throttle pedal was at when it started.
What you're trying to accomplish by doing this is to vary the amount of air fuel mixture while cranking to a point that it'll start. On my single carb'ed 216 I have to use this method to restart just about every time. I use my toe to depress the stomp starter and my heal to depress the throttle pedal. It's not as hard as it sounds LOL....
Many times when these old engines shutdown they'll heat up the fuel in the float bowl(s) which boils over into the intake. This causes an overly rich condition that a warm engine doesn't need for restarting. If you're trying to start with the throttle closed at the idle position you're making it richer by restricting the air flow to the cylinders.
Slowly opening the throttle to wide open increases air flow which helps to lean it out during starting. Flooring the throttle hard during cranking results in squirting more fuel into the engine and this is not what you want.
All this may be moot as you've got 3 carbs where only one of them is needed to provide good performance. It does look good tho.
