Carb tuning and idle setting

If it starts when set to idle at 600 rpm, that’s because the butterflies are choking off enough air to give a rich mixture with the amount of gas that is pulled while cranking. Setting the idle higher obviously increases the amount of air that gets by the butterflies at idle. The engine needs a rich mixture to start, hence the reason for the choke plate. You definitely don’t want to change the mixture screws to make starting a simple turn of the key. Those should be set to make a warm engine run well, use a vacuum gauge to set them. My first recommendation would be to make sure the choke plate is closing as much as possible and take it as normal to bump the throttle once to start the engine and forget about it. If you want to tinker and don’t mind the possibility of doing something that most wouldn’t then it sounds like you could try to reduce the gap between the choke plate and the air horn to make the mixture a little richer. How do you do that without cutting off to much flow? Good question. No idea if it will have some unintended consequences. You don’t want to add something temporary that could fall off and get sucked into the engine. That’s why I would say just be happy your engine runs well, bump the throttle once when starting, and enjoy.

Quit fiddling Buck 

Many thanks!

on the trailer

Yes. I adjust the trailer jack height. Thanks