1995 spi runs half power

[Champ 1958]

Just bought this old 1995 spi Starts fine out of water sounds good. But in water only runs
like it just getting half of the power? When I turn the fuel on/off switch to off while I’m running it
in the water it has full power in till the gas Runs dry ???/

 

[Champ 1958]

Maybe it the fuel valve??

 

[Mraw]

First I would check compression 150 is great 130 is marginal. Next I would replace all grey fuel lines, rebuild carbs with only genuine miking kits including new needles and seats, replace the o ring in the fuel filter, replace fuel selector

 

[Champ 1958]

Awesome thx

 

[CrazyJoe]

Bypass the fuel valve and filter by running a fuel line directly to tank reserve
then to carb.

Also could be your fuel pump pressure pop off is bad