1971 Mercury Fuel Line Replacement

Hello, new to this forum. I recently began a rebuild on a 1971 Mercury 1150 Inline 6. I am looking at replacing the fuel lines. The current lines are all 1/4" , connections are with crimped fittings on the fuel lines and a 3/8" brass threaded fitting going to the fuel pumps and carbs. These fittings are not reusable, and locally I have found fittings with a 1/4" barb and the proper thread so I can make my own. However, a quick look shows the opening of these fittings is definitely smaller than the current fittings.

My question is, should I use these fittings, or go to a larger size? I am concerned the engine could starve for fuel. I could use a larger fuel line and fittings though; I'm thinking the intake on the carbs will restrict it to the same flow it has now. I just want to make sure it's getting enough gas, but I don't want it flooding either.

 

I suspect that the fuel pump is of the non mechanical driven diaphragm type?
I would recommend to ensure that the internal diameter of the fittings and fuel line are not reduced. If they are larger, the engine will not flood. If they are smaller, they could restrict flow. Better to err on the larger size, or
find a way to keep the Id's the same

 

A trip down memory lane for Merc lovers
The 1957 60hp Marathon Six, Mark 75/Mark 75A endurance test, in line 6

 

How much smaller?
If it's more than 25% (in area) then I would go with larger fittings.
Otherwise, do a wide open throttle test run and see if you have starvation symptoms.
Let us know.

 

Thanks for the responses, you have both confirmed my opinion, going to the larger size. I am not able to do a WOT test yet, the wiring harness was shot. I've rebuilt that, reconditioned the stator, rebuilt the fuel pumps (yes, the dual diaphragm types), waiting on the carb and water pump kits. Compression runs from 125 to 134. Now time to replace these fuel lines, I know these engines suck up the fuel and didn't want to lean them out so I will go to the larger size.

I really enjoyed the vintage film about the endurance run! That's really something! This motor is going on a 1962 Alumacraft Queen Merrie, my wife is handling the restoration on that, keeping the vintage look but with current electronics and comforts. She's really solid, stripped down to the hull now, no signs of leakage and a really great base to start.

Cheers!

 

Sorry Brian, I didn't think to point out you'd have to have everything back together and in the water to do a WOT test.
It won't be until then that you'll know if the smaller fittings are big enough.
If they fail the test then you'll have to go with the larger size, no?

But you didn't answer my question.
It doesn't matter, you're changing so many things you won't be able to troubleshoot anyway.
Oh well, good luck.

 

Interesting old video posted by Barry. A shame that the alloy used in the early Mercury outboards didn't like salt water, otherwise they were a beautifully engineered thing.

 

Are you sure the crimp ferrule can't be cut and the fitting reused?

 

Bluebell, sorry I didn't answer your question directly; your suggestion that a 25% decrease was too much was the opinion I needed. The fittings I found were definitely nearing that margin. The original 1/4" opening would be down to 3/16" using the fittings I found. The motor has been likely sitting since 2009, and the main fuel line into the engine split, so I am going to replace all of it. Troubleshooting problems will definitely be an issue! But the engine isn't safe to run at present.

Gonzo, never occurred to me to replace the ferrules, on car engines I've simply replaced it all. That would mean I get to buy a new crimping tool! Cool ( I always tell my wife, every new job needs a new tool!)

 

Gonzo, tested a couple fittings and yes, they can be reused. Thanks for the tip ! New ferrules ordered, along with the tool to crimp them.