1990 Yamaha 175 stumbles 33 to 3,800 rpm

[russelll01]

hello my name is Rusty I am a helicopter mechanic by trade and I have my own boat maintenance business nights and weekends. The problem is 99.9% of my work is on inboards and I bought a center console this spring with a yamaha 175 precision blend (1990) and am not afraid to say 2 cycle outboards new to me. Now as to why I am here when I bought the boat the 175 would turn up to 54-5,600 rpm and accelerate smoothly now she stumbles from 33 to 3,800 rpm and will only make about 44 to 4,600 @wot. I have changed the water seperator and the plugs, no help. When accelerating when the engine hits 3,800+ it acts like it was hit with nitrous, nice surge of power, boat drops onto plane and speed climbs but, as I said rpm peaks around 44-4,600 unless I over trim the engine when she cavitates slightly rpm will hit the 5,000 mark. Any guidance or susgestions would be nice.
Rusty
443-207-0885

 

[robert graham]

Re: 1990 Yamaha 175 stumbles 33 to 3,800 rpm

check fuel delivery system starting at the fuel tank pick up, primer bulb, quick disconnect on motor, fuel filter, fuel pump, then carbs. drain each carb onto clean white rag to see what's in it. with carb plugs out, pump primer bulb to flush carbs and float chamber needle valves. you may have to remove/clean carbs. the problem could also be with the fuel pump. Good Luck!