Not gas down cylinder, down carb throats. It would prove that your carbs are not feeding enough fuel. I trust you're choking it when you try to start it? One cause of hard starting can be when your rotary valve clearance is too much. The tolerances expand once the metal gets hot, and it allows one cylinder to pull air from the other vs pulling from the carb. These clearances can become too large on very high hour machines, or ones that ingested water (washed away oil long enough to wear).
But it doesn't sound like you're running till it gets all that hot, right? It starts once, then you shut it off, then it will not start again, right?
Also, I would check all your fuel hoses, especially the places where you have hose clamps. I had a loose hose clamp at the fuel/water separator, and it would suck air. It was intermittent too, as it changed based on how the ski was jostled. Air in your fuel line is compressible, and decreases the potential of the fuel pump. Having clear fuel line or maybe a see-through filter just before the carb can help you spot this issue.
As for tuning the idle, that must be done in conjunction with the Low Speed screw. There is a writeup on tuning these carbs at the top of the 2-stroke forums list (I think they call that a "Sticky").