Fuel pump priming.

[sogood]

Not exactly engine related, so hopefully I'm in the right place. Just wondering if a mechanical fuel pump needs to be primed, when a tank has been totally emptied, with no fuel in the fuel line. Can the pump suck air until the fuel comes through? If it has to be primed, what's the best method to use? Thanks in advance.

 

[Chris1956]

Are you talking about a sterndrive, outboard, inboard or what?

 

[Alumarine]

My I/O with mechanical fuel pump primes itself quite quickly after running out of fuel and refilling.

 

[sogood]

Are you talking about a sterndrive, outboard, inboard or what?

​Sorry, Mercruiser inboard with a mechanical fuel pump. Thanks.

 

[sogood]

Thanks marc c. Just wondered if there was a particular procedure. So, just crank it until the fuel comes through?

 

[GA_Boater]

Cranking after running out of gas can take a while and wear the battery down. To speed things up, sometimes dropping a little gas in the carb helps. Not much and put the flame arrestor back on before cranking.

 

[SOG3]

Can you not choke it like the older cars and trucks ? It will still take a few times cranking it over.

 

[GA_Boater]

Using the choke doesn't draw gas out of the tank, only the fuel pump does.

 

[Maclin]

I try to get some fuel into the carb bowl itself, not always easy to do. On my Holley(s) I got it in thru the sight level plug. With fuel in the bowl it will idle for a lot longer than just in the butterflies, and the fuel pump gets a good strong stroke, vacuum pull is a lot stronger and priming happens quicker.

 

[QBhoy]

Like GA and maclin say...it takes a while. Also a real risk of overheatimg and melting battery cables etc if it takes too long.
If you don't fire some fuel down the carb....don't crank it for too long. It will eventually come through.

 

[Old Ironmaker]

Be patient. Depending on age I would be more concerned that I would fry the starter before I fried battery cables. Another good reason to carry a good battery booster. You'd think I sell the things.

 

[Lowlysubaruguy]

How long does it actually take to fire off, actually count the seconds. I battle complaints from customers on starting and transmission engagement a lot what may seem like an eternity may not be as long as you think. If its 20 seconds or less to start your fine live with it. If your cranking for 45 seconds or more thats a concern like others mentioned. Cranking an engine 15 to seconds after sitting long periods may actually better for the engine than it is bad for starter battery or wires as long as the battery and cables are in good condition. Cranking a boat engine thats sat for a period will or should build oil pressure and in the long run be better than one firing off at fast idle with a delay in oil pressure after it fires off. Things that prolong cranking time condition and location of fuel pump and lines and fuel filter. Older fuel supply lines may actually draw air but not leak fuel. And ethanol is killing fuel lines left and right. Theres no pressure in the suction line ( tank to pump) so often there will be no sines of fuel leaking but air being drawn in here will slow the priming process same with a weak pump diaphragm the rubber swells and cant produce the vacumm it needs to draw fuel but may still make pressure after it starts. Restricted fuel filter delays everything at cranking speeds carb fuel pressure is low and especially low when cranking.

 

[Old Ironmaker]

lowleysaburu guy, hey you sound just like my marine guy. I want to look at the key when I cold start her and I want the thing to fire, immediately. The boat sits for 3 weeks and I expect it to start in a few seconds, not happening son. Once it does start cold, maybe 3 or 4 cranks and less than 20 seconds with the choke on for cold start then I can just touch the key and she fires right up, the next AM too. Patience all.