Mercury 450r seems to not be making full power. Help

**axm0z5h** · 02-18-2025, 02:55 AM

I had a used 450r put in a small light boat. 21' 1200 pound hull. Once out on the water we tried a 28p chopper but can't get full rpms. Tried a 23p on a rough day and got 6200 but maybe could have gotten 6400 if it was better conditions. A 450 should easily turn both of those props on a lite boat.

Does anyone have experience with these motors? I know the fuel line needs a 1/2" i.d. what about the fuel water separator? What size do the fittings need to be? SHould I check spark plugs, fuel filters, etc? There are no codes

**DangerNewb** · 02-18-2025, 08:06 AM

Originally Posted by axm0z5h

I had a used 450r put in a small light boat. 21' 1200 pound hull. Once out on the water we tried a 28p chopper but can't get full rpms. Tried a 23p on a rough day and got 6200 but maybe could have gotten 6400 if it was better conditions. A 450 should easily turn both of those props on a lite boat.

Does anyone have experience with these motors? I know the fuel line needs a 1/2" i.d. what about the fuel water separator? What size do the fittings need to be? SHould I check spark plugs, fuel filters, etc? There are no codes

Throttle position sensor would be a good start. Dealer needs to use their merc software to check it. When I got a new 250 v8 on a bass boat mine was way off. Engine ran perfectly just didn't make full power.

**axm0z5h** · 02-18-2025, 11:01 AM

I think we may have found the issue. Apparently the 450 when ran in saltwater is known to have corroded tensioner pulleys for the supercharger. If that happens the belt will slip and it won't build boost. Trying to verify this is the issue now