What's this little fitting for on my new fuel pump?

[FatBear]

The fuel pump on my old (1976) Mercruiser 120 gave out and I got a new one. The new one looks identical except for two things: it's not black and it has this little mystery fitting on the bottom. I have some black paint, so that's not a problem. But what do I connect this third fitting to?

The pump goes on the engine with the filter on top. (Just so you know what I mean by "on the bottom".) The fitting is a hose barb that protrudes downward at a 45 degree angle, so not exactly all the way at the bottom. It is below the lower diaphragm, so I'm guessing that it is to drain away fuel in case both diaphragms blow out. Could that be true? If so, what should I plumb it into? I don't want fuel just dribbling into the bilge. Or should I just remove the fitting and plug the hole?

Thanks,
--FatBear

 

[boat127]

Re: What's this little fitting for on my new fuel pump?

its a vent a clear piece of fuel line goes from that fitting to the carb its for if the diaphram in the pump gets a hole in it gas wont go all over the bilge and cause an explosion

 

[Bt Doctur]

Re: What's this little fitting for on my new fuel pump?

It takes a clear hose up to the carb to let you know the diaphram has ruptured, if you plug it the pump wont work.

 

[Danny Mc]

Re: What's this little fitting for on my new fuel pump?

The yellow hose from a marine dealer is the approved hose.

 

[FatBear]

Re: What's this little fitting for on my new fuel pump?

So where does the hose go to on the carb? There wasn't a vent hose from the old fuel pump, so there isn't a fitting on the carb for the other end.

Thanks,

--FatBear

 

[FatBear]

Re: What's this little fitting for on my new fuel pump?

I just took a serious look at the carburetor. There is a threaded hole in the side of the throttle body opposite the idle screws. It is centered between the two barrels and it is plugged with a screw in plug. Is this where I could attach a fitting and run a line from the fuel pump vent to the carb? It is the only place I can find on the carb to do so.

This is a "remanufactured" carb that I installed a couple of years ago. Thinking maybe I got the wrong carb, I went and looked at the old one which I still have. It does not have any possible place to attach a vent line.

I also discovered that the gasket that goes between the top part (air horn?) and the center part (where the venturis are) is being sucked into the barrels in the vicinity of the choke valve. No wonder the damned think suddenly shuddered and quit! So I guess I'll either have to get yet another carburetor or rebuild this one myself. The decision will rest on the answer to the earlier question about attaching the fuel pump vent line.

Thanks,

--FatBear

 

[imported_TheMan]

Re: What's this little fitting for on my new fuel pump?

The line needs to feed over the top of the carburetor, so if the fuel pump were to malfunction it would dump fuel into the carburetor and prevent it from exploding inside of your engine compartment.

While the yellow hose is commonly found from the manufacturer, i doubt the color is any kind of requirement. Back in 1976 they probably did not require the safety loop for gasoline. If you can find a method of ensuring the fuel would be dumped into the carburetor (j tubes) you should be coast guard legal... but maybe not approved. Again, need to check coast guard regulations.

 

[bugzy_1]

Re: What's this little fitting for on my new fuel pump?

On my '79 120 ( 2bbl Roch.) there is a 3/8" hose fitting ,brass, in the spot you discibed that is conected to the fuel pump overflow. I would think that you could replace the plug in yours with a fitting.I believe that is the correct spot for it according to the maual.
Good luck
FYI You can get a rebuild kit for that carb. for less than $25.00

 

[paultjohnson]

Re: What's this little fitting for on my new fuel pump?

The yellow hose from a marine dealer is the approved hose.

Does the hose actually come yellow ? I just replaced the ...yellow... one on my 86 with a clear one. I assumed the old one had just yellowed w age.. I would think it should be clear so you can see if there is fuel in it ??? So you would know your fuel pump diaphram had ruptured.

 

[haulnazz15]

Re: What's this little fitting for on my new fuel pump?

Does the hose actually come yellow ? I just replaced the ...yellow... one on my 86 with a clear one. I assumed the old one had just yellowed w age.. I would think it should be clear so you can see if there is fuel in it ??? So you would know your fuel pump diaphram had ruptured.

Clear fuel line will work the same, but many manufacturers make the fuel line in a yellow tint brand new. Look at a new weedeater in a store sometime, you'll see the yellow-tint hose.

 

[jfrey8899]

Re: What's this little fitting for on my new fuel pump?

I got the same thing on my 71 mercruiser 140. I have a clear tube going from bottom of fuel pump into the side of my aircleaner. Galvanized nipple that goes through the air cleaner in case of rupture gas goes down the carb.

 

[Haut Medoc]

Re: What's this little fitting for on my new fuel pump?

The line needs to feed over the top of the carburetor, so if the fuel pump were to malfunction it would dump fuel into the carburetor and prevent it from exploding inside of your engine compartment.

While the yellow hose is commonly found from the manufacturer, i doubt the color is any kind of requirement. Back in 1976 they probably did not require the safety loop for gasoline. If you can find a method of ensuring the fuel would be dumped into the carburetor (j tubes) you should be coast guard legal... but maybe not approved. Again, need to check coast guard regulations.

Back in '76 they had the sight glass fuel bowl that was attached to the pump, the gas from a bad diaphragm would go there....

 

[FatBear]

Re: What's this little fitting for on my new fuel pump?

The only glass bowl I have is between the fuel tank and the pump and it has what appears to be a ceramic filter element in it.

But here's some breaking news. I just went up to Island Marine Salvage and looked at a 2GC with the fitting installed for a fuel pump vent hose. It is near the top of the air horn, not in the throttle body. They just drilled through the side of the carb between the two barrels - looks like 1/4" NPT threads - and installed a brass hose barb. They also told me that they have seen them installed in the spark arrester, but that seems kind of kludgy to me. I have two carbs and am going to rebuild both of them. I'll try drilling/tapping one before I rebuild it. If it goes well, I'll have a nicer installation of it.

Thanks,

--FatBear

 

[FatBear]

Re: What's this little fitting for on my new fuel pump?

I'm sorry I never completed this thread. I did get the yellow tubing (it is translucent yellow so you can see through it). I drilled a hole between the two air horns on the carb, tapped it (1/8" pipe thread), and screwed in a hose barb fitting. The yellow tubing goes from the fuel pump to the carb and looks totally professional - to my eye, anyway.

The boat actually ran fine for a little while after that. Then BLffftt. So I put it up for the winter. And the spring. And most of the summer. When I winterized it, I took the little bolt out of the drain hole in the exhaust manifold and apparently the threads came with it because it stripped going back in with barely more than finger pressure. I have had to replace the cylinder head and the exhaust elbow due to rusting through, so now I suppose it's time for the exhaust manifold. How is that to do? Will I need any special tools? I've got a lot of sockets, ratchets, and extensions, but no tricky ones and no torque wrench. If I try it, will I wish I hadn't?

Thanks,

--FatBear

 

[achris]

Re: What's this little fitting for on my new fuel pump?

Replacing the manifold is easy as. No special tools required, just a PROPER (not seloc or clymer) service manual.

Remove carb.
remove exhaust elbow.
remove alternator bracket
remove water hose
remove manifold
replace gasket and re-assemble in reverse order

Chris.........

 

[MarkySparky]

Re: What's this little fitting for on my new fuel pump?

Ya I agree on "PROPER" manual comment! I recently picked up the SELOC manual from local boat dealer. It's one of the worst service manuals I have ever seen, though better than nothing(sorta!). Google is your friend especially if you are stuck with less than optimal manuals. BTW, about that torque wrench- check your local auto parts store and see if they have a tool loan or rental program. You basically put down deposit equal to tool purchase price and bring tool back a few days later and get money back. I've done that several times with tools I know I'll rarely use.