Big block engines that run at 270 plus degrees won't fire when shut down....or not easily.

Try this: Make sure you aren't lean, just tweak the hi speed back about 1/8.

On restarts, advance the throttle trim a little (to open the carb), and then squeeze the throttle and release. Then pull few times with no glow warmer, then proceed to start as you usually do. You might have to advance the throttle trim a little more.

You'll get used to how far advanced the throttle will need to be to start it. Hot big blocks do not like to start.

Now, it is possible you've over heated the engine too many times (and ruined the compression...)...but try my way first.