Mercruiser 160 carburetor

[gregg_a_g]

My "free boat" had a 165 Inline 6. The block was cracked. Removed and disassembled the engine. Most everything looked good except the block. The carburetor is a little
cruddy, but probably serviceable with a rebuild (Rochester 2GC).

I bought a 160 from a salvager that looks really good. The fuel pump has a line to the
bottom that goes to the front of the carburetor (also a Rochester 2GC, but in excellent condition). Achris says that if the diaphragm fails the carb will flood the engine and prevent fuel from getting into the oil pan. I don't quite understand...

If the line from the bottom of the fuel pump on the 160 is a safety in case of diaphragm rupture, why doesn't the 165 use one? If I use the valve cover from the 165 it doesn't have a fitting for the return line from the tee in the carburetor. Would it make sense to add a fitting to the 165 cover and use the 160 carburetor with the tee and extra line from the fuel pump? Or would it be better to use the fuel pump from the 165 without the extra line? I'm not quite understanding the situation... If the fuel pump diaphragm ruptured, wouldn't the fuel pump just stop pumping? I would like to use the 165 valve cover because it has a breather fitting that goes to the flame arrestor.

I'm getting an elbow to reconnect the cooling lines later this week. Then I just need to
install points and do a little wiring. The 160 is bolted to a pallet and I'm shooting for Sunday to try and fire it up (testing before lifting into boat).

 

[achris]

Post photos of the different set ups. Having trouble visualizing...

 

[Bt Doctur]

Auto pumps are vented to the atmosphere, marine [umps vent to the carb so you dont blow yourself up. All mechanical pumps must be vented to operate the diaphram.

 

[gregg_a_g]

Here is an annotated picture of the 160. The valve cover had a "breather style" cap (which I lost in transport), not a cap and a separate breather to the flame arrestor (like the 165).

 

[achris]

If the line from the bottom of the fuel pump on the 160 is a safety in case of diaphragm rupture, why doesn't the 165 use one?

Possibly because a) someone put an automotive fuel pump on or b) someone didn't know what that clear length of tygon tubing was for and just threw it out (hint hint, don't buy a tube from Mercury, just head to the local hardware shop and buy the right size tygon), or c) it's a dual diaphragm pump with a sight glass. See below.

If you see fuel in the sight glass, replace the pump. That sight glass is connected between the dual diaphrgams, and if the pumping diaphrgam ruptures, the sight glass will fill with petrol.

If the fuel pump diaphragm ruptured, wouldn't the fuel pump just stop pumping?

Eventually yes. But only after the engine has consumed all the fuel already in the float bowl, and by that time, you have either an engine sump full of petrol, or a bilge full of petrol. Neither of those scenarios end with 'and they lived happily ever after'!

I would like to use the 165 valve cover because it has a breather fitting that goes to the flame arrestor.

Good choice.

I'm getting an elbow to reconnect the cooling lines later this week. Then I just need to install points and do a little wiring. The 160 is bolted to a pallet and I'm shooting for Sunday to try and fire it up (testing before lifting into boat).

Good luck.

 

[gregg_a_g]

Ah, okay. I think I get most of it now. In the pre-1975 days, there wasn't a fuel vent safety line requirement, yes? And there were lots more fires, yes?

In the picture I posted above, you can see there is a "tee" at the airhorn connection on the carburetor. One line goes to the clear tube from the fuel pump vent, and the other makes a little loop and goes into the valve cover. What is the purpose of the line to the valve cover? As I mentioned, the 165 valve cover has a separate breather that connects to the flame arrestor on the 165. So I'm planning to use the valve cover and flame arrestor from the 165. Should I connect the "2nd" hose from the tee to the breather hose (with another tee), or should I drill a hole in the 165 valve cover and connect it there?

 

[kenny nunez]

The Tygon hose should only connect the rear of the air horn to the fuel pump vent. Use the 165 valve cover with the vent tube connected to the flame arrestor as you posted.
Engines with the plastic bowl connected to the fuel pump as in the picture Chris posted had the short hose that went between the rear of the air horn to the hole in the valve cover.

 

[gregg_a_g]

Ok, I'm a little confused. Do you mean use the 165 valve cover with the "breather vent tube" from the cover to the flame arrestor? And then remove the tee at the carburetor and only have one connection from the rear of the air horn to the fuel pump?

So only the dual diaphragm pumps with the sight glass had another connection from the air horn to the valve cover (with a tee)?

 

[kenny nunez]

The “T” that is on the 160 was something the previous owner added. Just remember all marine fuel pumps with the small male fitting for the Tygon hose must be routed to the carburetor’s air horn so that the fuel stays out of the bilge and into the carburetor only.
The style that Chris posted can also be converted by removing the bowl and adding a fitting to route a Tygon hose to the air horn.
Use the 165 valve cover with the vent hose routed to the flame arrestor and you will be in good shape.