You need a bigger motor?��
Pic could be deceiving but your pump intake looks bigger than your cylinder bore by about 1.5x! Other than that I just wish it was mine!
looks newer than the one I have, I put mine on an 11hp brigg's if you need a foot valve might get a rebuilt 4" Sure-Flo from farm/irrigation store
I just have mine set up with straight hose then use a bilge pump with an atv battery to prime the pump.
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this is what it looks like now;
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