i have a 18 hp twin cylinder volvo diesel which is only running at approx. half speed .i replced the fuel filter and removed the tank and cleaned it out and filled it with clean fuel.the injectors are working fine i was told to loosen one at a time and see if she slowed down and it did.i dont know what else to check.this happened suddenly last fall before i put it away for the winter.and i did all the things listed above since i put her in the water two days ago.can anyone give me advise om what to do.