Not familiar with the oil plumbing on the SOHC engines, but with regards to the gasoline issue, have you gone through the carbs and floats to clean/rebuild them? If not, the easiest 'fix' might be to add 1 oz. of
SeaFoam to the full gas tank [should read, "1 oz. of
SeaFoam per gallon of gasoline"], run it for 10+ miles, then let it sit overnight, and try it again. The
SeaFoam will dissolve varnish deposits in the fuel system. By running it for a while, you circulate the
SeaFoam'ed gasoline throughout the system (including the carbs); by letting it sit overnight, you give it time to dissolve the deposits.
I would also recommend you use
SeaFoam in the crankcase, once, to remove carbon sludge from within the engine, and the transmission. Add 1-1/2 oz. of
SeaFoam per quart of oil. I ran my bike on the centerstand for five minutes, shifting through all five gears while idling, to flush out the transmission. My oil went from caramel color, to coal black, within that short time. Then I changed the oil, and the filter (traps a lot of the carbon sludge freed up). Repeated it 5,000 miles later, and the oil never changed colors (no sludge to dissolve); changed the oil after 120 miles, just to be safe, as the
SeaFoam does thin the oil a bit. Did this on my two cars, and my truck, also. No issues, even after 30,000+ miles on the four-wheeler's since the clean out's. Safe, effective, and worth the time and money, IMO.
If
SeaFoam in the gas tank doesn't work, then you will need to disassmble the floats, and/or carbs, possibly replacing parts. Best of luck! Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII