Dear Bax,

I have OS 91 FX mounted inverted in an aircraft having severe fuel flow problems. Can you provide a schematic of tank location wrt to needle valve for inverted mounted engines?

Secondly I am using a fuel tank with plastic nozzle on top for air with no tube protuding in the tank. In most of the OS engine manuals the diagram for Fuel tank shows fuel tanks with air tubing protuding into fuel tank bent at 90 degrees. Which one is better for aerobatic flying ? My 91 FX starts to cough when I do Knife edge.

Regrds,

Khizer

There really is no schematic for fuel system/tank installation on the O.S. Max .91 FX. You basically set the fuel tank in the airplane such that it's immediately behind the firewall and positioned so that the centerline of the tank goes through the center of the carburetor or is no more than about 3/8" lower. If the front of the tank's more than a few inches away from the engine, a pump or pressure/regulator system should be used.

Non-pump plumbing of the fuel tank would have the clunk line going to the fuel inlet nipple at the needle valve assembly. The muffler would provide pressure to the tank which, ideally, feeds to the forward top of the tank. It's also used as the overflow line when fillling. You fill through the fuel line. If an additional line is used for fueling, it would ideally go to the forward bottom of the tank and would be capped when not being used for filling.

Pumped engines would have the plumbing diagram with their instructions.