1994 rude 50 hp

[dieselcat]

A friend of mine has this motor and is only getting 4500-4600 RPM'S out of it at WOT.I am told it should be between 5500-6000 RPM'S.We have rebuilt the carbs,found out needed a new coil and replaced it.The motor is on a Lowe 17 ft aluminum bass boat and has a aluminum prop=12 1/4 X 15 pitch.As far as i can tell it looks like the factory prop that came with boat and motor.Any ideas as to what to check for that would be causing it not to get the right rpm's?

 

[jonesg]

Re: 1994 rude 50 hp

Baseline it,
compression test all cylinders
and spark gap test it 7/16ths inch blue spark should crack!
Run it on a test fuel tank, bypass any filters.

I woulda changed all the coils too , plugs and plug wires.

 

[tashasdaddy]

Re: 1994 rude 50 hp

if the motor is running correctly, it is time to fine tune the boat/motor set up. the AV Plate should be 1 - 2inches above the keel of the boat, trim needs to be addressed, and the prop diameter and pitch addressed. the prop he has is a very middle of the road all round prop.

moving this to prop forum.

 

[dieselcat]

Re: 1994 rude 50 hp

Did a compression check and got 150 on both cylinders,and the coil on this motor is a 2 in 1,so both coils are new.even if we went down in pitch it's not going to give him the xtra 800 rpm he needs unless we went to a 11 or 12 pitch.Most boats that are comparible to this one that i have looked at all have had either a 15 or 13 pitch prop,so judging by what i've seen i'm assuming it is already proped right.Can and will timing effect the rpm output of the motor?