I am building a Ultra Hots. Has a ST 3000 engine. Going to mount it inverted. Haven't ever done this before. I have a DuBro 20oz tank. Cap is towards the top of the tank, not in the middle. Woud you want to put the tank in upside down and with the vent still towards the top. Or would you put it in as you would for a motor mounted up right. Just wondering what would be best?

JIM

The fact that the tank stopper is slanted up with standard upright mounting has little bearing on anything other than length of fuel draw from clunk to carb. I have seen suggestions that this length s/b nmt 7" but I have seen engines draw w/no problem at longer lengths. But obviously shorter length = better draw, esp since you will want to spend a lot of time hovering.

I like to have vertical center of my tank level with spray jet for equal head flying upright/inverted.

If it would save you an inch of fuel line length, I would not hesitate to angle the front of the tank down toward the needle valve, but still put your breather/pressure line at the top of the tank, even though the bubble w/b at the bottom.

I hate to splash cold water, but question the ST3000 as a good choice for this plane, as it is notorious for mid-throttle problems. There are solutions, but they are black art type. Much of the fun of the UltraHots depends on throttle management, and the ST likes to go either fast or slow, but doesn't like to be managed. If you are not adept at reworking ST carb, I hope you have access to someone who is.