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OS FS-120 Surpass II Rebuild Question

Old 05-30-2015, 04:00 AM
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Default OS FS-120 Surpass II Rebuild Question


A friend asked me to look at a Surpass II for him which he got on Craigs List. The engine does not look like it has much time on it, but I've been advised that the pump may be shot. I also notice that there is a crack around one of the mounting hole flanges on the backplate.

If a replacement pump is not available (and I don't believe that it is), would it be possible to replace the existing pump and backplate with an OS FS-120E backplate p/n 45507010 and run it as a conventional engine using only muffler pressure???


Old 06-01-2015, 06:26 AM
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On the O.S. FS-120 Surpass II engine, the pump is just a pump. The regulator is on the carb. If the pump moves fuel, it's working as it should.

If you remove the pump, and want to use the conventional rear cover, you'll also need to change the intake manifold and carburetor. The original regulator carburetor for the pump version won't work on suction and muffler pressure, and the non-pump carb won't fit in the pump version intake manifold. You'll also need to either replace the crank or grind off the stub shaft that engages the steel pump drive disk on the rear cover. It turns out that it's not a cheap conversion.

Unfortunately, some parts specific to the FS-120 Surpass I, II, and E (non-pumped version) are not available any longer. Check your retailer for details on the ones they can order.

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