TOPIC: Fuel pump addition to 1960 Mercury 400 long

My 400 only has 1 fuel pump but has a place for 2 on the side of the block. What do I have to do to actiivate the second fuel pump? I know that I will have to buy the fuel pum and all of the diaphrams etc. But is there any way to get vacuum to the pump or do I have to drill passages.
I ask this because I know the larger 4 cylinders use the second pump and I believe it is at the 500 level.
My 400 will not run above 3/4 throttle for very long on the Atwood tank without removing the cap and I have drilled out the vent hole once. It helped.
My assumption is that because of the type of fuel pump the difference in pressure is not enough to pull fuel at the higher rpms against a small vent. I believe the 45hp 400 may be just on the cusp of needing the second pump.

you don't need a second pump. find out what the problem is with your tank. a second pump will compound the problem.

I agree with Dave. The motor was designed with a single fuel pump leave it that way. Those are screamer little 45 HP motors. You have a problem that needs to be chased. Start with the tank, then the hose then the existing fuel pump (have do replaced the diaphragm kit??) then the carbs

I have replaced the diaphram on the fuel pump and the Mercury tanks have no problem feeding the engine at 3/4 throttle or full throttle. I am chasing high rpm power problems that seem to be carb related running rich. I will forget about the extra fuel tank and drill the vent hole out one more drill bit size.
I do know my manuel cautions on using aftermarket fuel tanks.

Some of the aftermarket fuel tanks have amazingly small pick-up tubes and a very small screen device that can really restrict fuel flow and risk a lean condition - piston melt-down.
Other after-market fuel tanks do not have a steel ball in the female fuel connector - and have a flat disk instead.
The flat disk style won't allow enough fuel past it to feed a larger 4 cyl - like an 800 or 850 - or any inline-6, but 'might' be okay for the smaller 40 & 44ci Mercs like you have.
Leaking valves in your fuel pump will also cause the fuel pump to fall behind demand too.
The second fuel pump boss is there for the race guys running alcohol and need a TON more fuel flow.
Thom

Actually, the second fuel pump boss was for the Mark 30 (which shared a similar casting back in the mid 1950s when they built the first diecast block 4-holers). The Mark 30 used two fuel pumps as the smaller crankcase volume did not draw enough fuel at idle speeds. None of my 4-cylinder racing motors have two pumps...
- Scott

OK, that brings up a question about my Mark78. I have one of the plastic red 6gal tanks and seem to have some probs w/ power at wot. What can I do with tank to ensure i'm getting enough gas? Thx, Joe

I think it might bear mentioning here that evidently all red plastic tanks are not created equal. I've run the Tempo brand (6 and 12 gal) tanks for the last three years, on two different motors (stack six Merc and V4 OMC - both very thirsty motors) and never had an issue. A trusted marine dealer here told me they were still made in the USA (Texas, I believe) and were a better quality than other plastic tanks on the market. Don't know if all that's true, but they've worked well for me.....