ORIGINAL: tony0707

HI
I have endless experience running the OS 61 sf engine with no pump on 15 % morgan omega fuel
my first thought is the diaphram in the pump has dried up and gone bad as they will over time might try to get a stock no pump back plate if you can-,no parts are available for the pump if you need a pump you can run an external perry pump off the stock backplate with a pressure fitting
the bearings in these engines will last for many years using the fuel i suggested if you run the engine correctly-not lean ! the engine is extremely user friendly
the air in the fuel line appears to be from the pump so my recommendation above
be very sure that all gasket surfaces are clean an no air is getting into the crankcase anywhere
the engine will run hot if air is getting in
do not attempt to adjust the needle valves when the engine is hot it must cool completely down before each run-,then start tune over
i run a 12/6 or a 13/6 apc on my engines i have three 61 sf's and been running a 61 SF for 20 years that i s when they first came out
BEST REGARDS TONY