3.0 mercruiser i/o

[Pdevito]

I have installed a shut off valve on the gas line to stop carb clogging when not used for a while. Carb is rebuilt. My question is should I install a bulb or is it fine to just start up. Don't want to damage fuel pump. Any advice is welcome.

 

[Bondo]

Ayuh,..... Welcome Aboard,..... Where'd ya put the valve,..??

Doubt it'll hurt anything,.....

 

[Scott Danforth]

I have installed a shut off valve on the gas line to stop carb clogging when not used for a while. Carb is rebuilt. My question is should I install a bulb or is it fine to just start up. Don't want to damage fuel pump. Any advice is welcome.

the valve is not needed
do not install a bulb
the crud in your tank (water, etc) is what will clog up your carb. not using it often just lets the fuel in the carb evaporate which accelerates the debris in your carb to harden in the passages.

 

[Pdevito]

Ayuh,..... Welcome Aboard,..... Where'd ya put the valve,..??

Doubt it'll hurt anything,.....

Near the tank. My question do I need a bulb for start up as I run it out of gas when not being used for a while so varnish dosent build up.

 

[Scott Danforth]

Near the tank. My question do I need a bulb for start up as I run it out of gas when not being used for a while so varnish dosent build up.

using a shut-off valve and trying to run it out of fuel will kill your fuel pump unless its an electric pump and you simply turn off the power to it. however trying to run an engine driven mechanical pump against a closed inlet will result in a torn diaphragm

 

[Pdevito]

That's what I thought thanks

 

[Pdevito]

That's why I wanted to install a primer bulb. Will that solve?

 

[CaptnKingfisher]

That's why I wanted to install a primer bulb. Will that solve?

No.

Because everytime you shut off the fuel valve, the fuel pump is running and sucking on a vacuum and putting a strain on your pump. A primer bulb wouldn't do anything to stop the damage that occurs when youre shutting down the engine by shutting off fuel.

 

[achris]

A) If you want to run the engine until it stalls out due to too low fuel level in the carb, put the shut-off valve between the pump and the carb. The pumps are designed to hold pressure against a closure (think full carb fuel chamber, needle valve closed), not pull a hard vacuum, like @Scott Danforth said.
B) Closing off the fuel (either way, before or after the pump) and running the engine until it stops does not completely drain the carb of fuel, it just drains enough out of the float chamber to make the mixture too lean to fire. You'll still have 'plenty' of fuel in the carb...

I've just posted a reply to a thread man-splaining exactly this point... Click HERE to read it.

Chris......

 

[Scott Danforth]

the main question is why would anyone want to add a leak point or the potential to take out a pump such as a shut-off valve to a fuel system? simply using the boat once a month will keep the carb full of fuel and keep varnish at bay. the anti-siphon valve prevents any fuel from continuing to run to the carb

 

[achris]

the main question is why would anyone want to add a leak point or the potential to take out a pump such as a shut-off valve to a fuel system? simply using the boat once a month will keep the carb full of fuel and keep varnish at bay. the anti-siphon valve prevents any fuel from continuing to run to the carb

While I am in complete agreement with you on all points, I have in the past been forced to put shut-off valves in boats. Most of the yacht clubs locally have it in their regulations that power boats must have a fuel shut-off valve. There's no point trying to explain to them all the negatives... "It's in the rules" is the only answer you get...

Chris...

 

[Pdevito]

I have installed a shut off valve on the gas line to stop carb clogging when not used for a while. Carb is rebuilt. My question is should I install a bulb or is it fine to just start up. Don't want to damage fuel pump. Any advice is welcome.

BZ ZZZ

 

[Pdevito]

Fuel injection disent have the same issue as th 2bbl mercarb with accelerater pump

 

[Scott Danforth]

Fuel injection disent have the same issue as th 2bbl mercarb with accelerater pump

And oranges are not apples

Your point is what?

Fiel injection relies on a high pressure pump, a throttle position sensor, a map sensor, a bunch of data tables and an ecm to enrich the mix during a throttle open event

A carb relies on a small diaphragm in the fuel bowl connected to the throttle linkage and an orifice to meter its delivery during a throttle open event

However both systems would suffer a fuel pump failure if you put a shut-off valve before the pump

So, please clarify your comment

 

[Pdevito]

Thanks for that update someone told me that fuel injection didn't have the same issue cause it was an electric pump Sounds like you have really good advice there thank you

 

[achris]

Thanks for that update someone told me that fuel injection didn't have the same issue cause it was an electric pump Sounds like you have really good advice there thank you

Later carbed engines also have electric fuel pumps, but still have the issues that carbs have. It's not about the pump, it's about the metering and delivery system (carb vs Injection)...

 

[Lou C]

The difference is that an EFI or throttle body system stays full of fuel that is not exposed to air between the fuel pump & the injectors. A carb bowl has to be vented so the fuel in the bowl is exposed to air and it oxidizes and evaporates leaving deposits behind. With small engines used on yard equipment they have fuel shut offs and drain valves on the carb, as do some outboards (like our Suzuki DF 2.5). But on an inboard a fuel drain on the carb could be a safety risk (yet if your think of it, you can use a Racor filter with a metal bowl & drain on an inboard).
I guess if someone knew they were not going to use the boat for more than a year they could get the tank pumped out, & remove the carb & dump all the fuel out of it & reinstall the carb.
After being stored for 6 months with stabilized E10 gas (all we can get here) after cranking it over 3 times my carbed engine has started every season.

 

[achris]

... a safety risk (yet if your think of it, you can use a Racor filter with a metal bowl & drain on an inboard)...

Yes but by USCG regs, that style of filter is NOT allowed to be in the engine compartment. (And yes I know, most people mount the damn thing right next to the engine!)

 

[Lou C]

I knew that the plastic bowl was not allowed on inboards but I thought the metal bowl was allowed….

 

[j cat]

I have installed a shut off valve on the gas line to stop carb clogging when not used for a while. Carb is rebuilt. My question is should I install a bulb or is it fine to just start up. Don't want to damage fuel pump. Any advice is welcome.

I use the gas valve shut off valve in the fall ...merc 470 . carb ...run it and then the fuel pump and carb stops the gas runs at idle and then the engine stops.
then I remove the carb filter and the fuel pump filter and I clean it and I is no fuel in it..
then I remove the fuel tank gasoline ... put it in my truck...