Chev 350 Inboard

[kapnD]

Vacuum hoses tend to self seal under suction, you’ll seldom find them clamped unless they’re situated so that their weight will pull them loose from the barb.

 

[mikealston2428]

Great thanks for clarifying that

 

[Mr Efficiency]

I suspect the boat was laden down with Marlin, and couldn't get on plane !

 

[mikealston2428]

LOL

 

[brendan gardam]

Just a quick question
The small hose size of the carburetor vacuum today fuel pump is very small
Are there hose clamps this small.

no, vacuum hoses just push on friction fit. if you are worried you can use small cable ties for a clamp.

 

[mikealston2428]

Thanks Brendan,
I've ordered new filters and a marine mechanical pump
I've also decided to replace the spark plugs
Once it all done I'll drop the boat in the water and see if problem sovled and I'll let you all know
Thank You to all members that gave me advice
This forum is fantastic I greatly appreciate the help
Cheers
Mike

 

[missinginaction]

You're welcome Mike. Please let us know how you made out when you have time.

 

[mikealston2428]

I definitely will Missinginaction

 

[mikealston2428]

Hi All,
Just confirming clear tygon tubing is used for vacuum line from mechanical fuel pump to carburettor vacuum port
Also what is the diameter of this line
Cheers,
Mike

 

[Barry]

That vacuum port on the back of your Quadrajet (just be sure it's pulling full manifold vacuum) can take the line from your mechanical fuel pump. It's not exactly a return line. In the event that the diaphragm on your fuel pump fails, the leaking fuel will be contained inside the pump body. Engine vacuum will pull this fuel directly into the engine causing the engine to stall due to flooding. This keeps the fuel out of the bilge. You probably already know that but I just thought I'd clarify for anyone else reading. Good idea to get that automotive style pump out of there whether it's bad or not. 6-7 psi sounds about right for pressure any marine pump for a small block 5.7 liter Chevrolet engine will be fine. I'd change the filters while I was in there, they're cheap and it can't hurt. Good luck, MIA

Holley 712-327-11 110 GPH Mechanical Fuel Pump -Marine https://www.holley.com/products/fuel_systems/fuel_pumps_regulators_and_filters/fuel_pumps/marine_pumps/parts/712-327-11

If you hook it to the vacuum line, will not the diaphragm pulse the vacuum, or is the fuel pump, dry side of the diaphragm vented to the crank case. If not vented to the crank case, would the pulse of the diaphragm interfere with a
vacuum advance

Every one of the marine engines that we bought from engine upfitters, had the overflow line attached just under the flame arrestor on the arrestor itself

 

[missinginaction]

Barry, you're right! As soon as I read your post I remembered where this safety line from the fuel pump attaches to my carburetor. It's not drawing vacuum, it is up on top of the carburetor under the flame arrester exactly as you said.

I'm not sure if putting vacuum on that line would make any difference as far as fuel pump performance is concerned. My intuition tells me it wouldn't matter but I'd have to check it and see. Regardless, you're right that the line is attached on top of the carburetor so there isn't any vacuum on it.

Mikealston, I'll post a link to the carburetor that I use. It's a Holley marine carburetor so it's a bit different than a Q-jet. Look at the picture. Look at the top of the carburetor, where the flame arrester fits on. Look at the flange and next to the secondary bores on top of the silver fuel line that connects the primary and secondary float bowls you'll see it. There is a small port there with a black rubber boot on it. That's what Barry is talking about. So it's not really pulling vacuum but in the event of a fuel pump failure it will allow fuel to flow from the pump to the carb as a safety measure.

Holley 0-80364 450 CFM Marine Carburetor https://www.holley.com/products/fuel_systems/carburetors/marine_carburetors/parts/0-80364

Thanks for straightening me out on that Barry. My mistake.

Regards,

MIA

 

[mikealston2428]

Hi Barry And Missinginaction,

Thank you both for clearing that up for me
My flame arrester has the fitting on it above the secondary bores
So the fuel pump overflow fuel will drain into the secondaries

So I understand this would flood and stall the engine which in turn would let me know the first pump diaphragm has perforated

If I then ran the line from the fuel pump straight into a jerry can (which I always have onboard) I could then get the boat back to the boat ramp with the last pump diaphragm ? ?

Thank You Again Team,
Mike

 

[gonzo]

The small hose from the pump to the carburetor is clear vinyl to let you see if any fuel is leaking. It doesn't need hose clamps, zip ties work fine.

 

[missinginaction]

No problem, my apologies for forgetting where that line goes in the first place. I've never had a fuel pump fail, so I don't know exactly what would happen. In the automotive world we don't use mechanical pumps anymore since everything is fuel injected. In the old days a failed pump diaphragm would cause the pump to leak and you'd see/smell gas under the car. My understanding is that while a diaphragm can fail and flood out your engine, it is more likely to fail slowly. This is why the tubing running from the pump to the carburetor is clear. When you're checking oil/doing a pre-trip inspection just take a look at the line. If you see any liquid in it that's a red flag.

 

[mikealston2428]

Hi Guys,
Ive ordered some Tygon hose for pump to carb
Ill let you know if Ive solved the problem once I've put the boat in the water
Thanks,
Mike