I'll stand by my previous post. Having worked with 2 strokes for quite some time now and small engines in general, two stroke small engines make their power at full throttle or close to it. Its detrimental to a small 2 stroke engine to run it at half throttle for extended periods of time, and burns off more carbon, makes more power, and is most efficient at wot or close to it. Think of it this way, You can lug a 4 stroke more because it has a wider power band starting at a lower rpm range up to full throttle. 2 strokes dont lug well at all, and make their torque at high rpm, aka full throttle. More torque, more cutting power. Lawnboys are governed as to not run as fast as string trimmers or chainsaws but still achieve optimum cutting efficiency when running at peak. I'm basing my post on experience in working with and rebuilding/tuning 2 stroke jetskis, lawn mowers, trimmers, chainsaws, etc. All engines have sweet spots, 2 strokes are made to rev and run at higher rpms constantly due to their much smaller power band.

You really can't gauge fuel consumption differences very well between engines in the same series in the field. There are too many variables. Grass height and moisture, humidity and temperature. The settings on the carb and the wear of the parts. Your findings really only apply to your 2 mowers and are not representative of commercials vs standards in general. You will always be burning more fuel when running at a higher RPM with your mower. That is unless you are bogging it in tall or wet grass and the governor is opening up all the time.

Where in the H did you find a new 10324? The float in the carb will stick sometimes. Install your shut-off on the fuel line and use it. The fuel line has a typical 2-cycle strainer on it inside the tank, but the extra in-line filter won't hurt anything if can find room for it on the fuel line with the shut-off. When the float sticks, pick up the back end of the mower and drop it on the lawn from about 6" a couple times. This usually straightens them out. Do you push the throttle/choke lever all the way down to 'choke' when starting, then pull it back a little to the 'run' position? The Seafoam is a good idea, but put it in the gas can with your 2-cycle mix and use it all the time. It's not an instant answer to anything.

I checked my owner's manual and indeed - it states this is an OHV low emission engine. I assure you it is not ohv. the engine performance improved when you partially closed the choke. This is an indication of a lean fuel air mixture. The fuel pumps are usually very reliable, but there could be a leaking diaphram. My suggestion is to renew the entire carburetor and fuel pump. The pump pulse hose should be clamped. Hoses develop cracks and become hard - especially around the ends. Air leaks are common. I know you replaced a section of hose. The fuel hoses around the engine frequently become hard, then cracks form. The fuel pump draws in air. Also the ends of the fuel hose also allow air leaks. The current ethanol fuel sometimes leaves residue on valve stems. The valves may not be closing fully due to sticky valve stems. There could be excessive carbon on the valve seats and in the combustion chamber. The opposed twin was a great engine and is well worth maintaining provided the equipment is in reasonable condition.