1969 Mercury 9.8 afraid of the lake.

[gene4christ]

1969 mercury 9.8 outboard runs great in barrel but not on the boat. Not sure where to post this, I didn't find anything in the search topics. The motor runs fine in the barrel but will not run when on the boat at the lake. Any help will be greatly appreciated. Thanks

 

[Texasmark]

Barrel is no load. Lake isn't. Probably clogged fuel passages from sitting up. Could be low compression. 120 psi and within 10% are good numbers

 

[gene4christ]

Thanks Texasmark for the response.
We were thinking maybe the fuel tank or something because when we have the motor in the barrel the tank is on the table about the same height as the motor. It won't even start when on the boat at the lake. So thought it might be a fuel delivery issue.

 

[dkonrai]

Thanks Texasmark for the response.
We were thinking maybe the fuel tank or something because when we have the motor in the barrel the tank is on the table about the same height as the motor. It won't even start when on the boat at the lake. So thought it might be a fuel delivery issue.

Hmm fuel pump?

 

[MH Hawker]

it is more than likely needs tuning on the lake, its a back pressure thing

 

[Texasmark]

it is more than likely needs tuning on the lake, its a back pressure thing

The final tweak for my carbs was to be the hole shot on the water per the SM. Made sense as that was the worst case load. The exhaust relief ports st the top rear of the mid section are supposed to relieve pressure due to the exhaust pipe being submerged on the water, but who knows till the problem is solved.