Okay Here are 2 versions of the LT-40 Fuel tank. The kit version has a flat bottom which makes it abvious that the flat part is on the bottom, The ARF version is Round but 1 side is larger than the other as seen in picture. My question is, I am working and almost done on the ARF version but I cant figure out which part of the fuel tank goes on the bottom and which goes on the top? Please see picture in order to understand what i'm saying. Is the way I have it now the correct way? it seems the shorter end on the bottom fits better through the hole of the firewall going to the engine but I doubt its the other way.THANKS!

In the picture, they are both sitting right side up

my advice would be to insert it in whatever way it best fits the hole in the firewall. seems logical...

okay So it doesent matter which way I put the fuel tank? here is another one.

It doesn't matter. Fit it in however it fits the firewall best. Just be sure to install the tubing so that the vent is at whatever you decide is "top".

I've mounted tanks on their sides and upside down in the past for various reasons (tanks that have little bubbles on top for the vent line, for example). As long as the vent line goes up, how the plastic is shaped doesn't matter at all.