The oscillating pump, which is the recommended one to use with 4-cycles, needs to be mounted to the engine perpendicular to the crankshaft. Since you should be mounting it to the engine the soft mount will not affect performance. With a little modification I was able to use the mounting plate that is included with the pump. Basically I drilled two new holes in it so that the pump cleared the cowl and mounted it off the bottom two screws of the rear crankcase cover. With the engine mounted inverted the pump is above the rails of the mount ,close to the inside of the top of the cowl. (Hopefully that makes sense. I'd send pictures but I'm traveling). It doesn't quite meet the the 1.5" from the crank centerline that Perry recommends but it's close enough that I have not noticed any performance issues. The pump will not work if mounted to the firewall when using a softmount.