Help: Replace primer bulb with electric pump on 2stroke Merc 135 V6

kwik_uk

Petty Officer 2nd Class
Joined
May 25, 2011
Messages
155
Hi guys,

Some of you might remember me from my bare shell Dateline Bikini (Sidewinder clone) full rebuild and re-power from 2012.

I’d like to add an electric primer pump in line with my primer bulb. So I’d keep the bulb for emergency starting, but on a day to day basis I’d like to prime the outboard using an electric pump, with a “push to prime” button. When the button isn’t pushed I’d obviously need the pump to allow fuel to flow through it unhindered.

Has anyone done this? And if so can you provide me with some info on how it can be done please?

So far I’d considered a 12v gasoline in-line low pressure pump before the primer bulb, and a push-to-make switch or rocker switch on the dash. See the items I’ve found below on eBay as rough examples:

Fuel pump: https://www.ebay.co.uk/itm/323857045463

Fuel primer switch: https://www.ebay.co.uk/itm/362740514211


Would very much appreciate any insight or ideas you guys might have :)
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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47,309
Why not fix rhe mechanical pump, adding an electric pump is a good way to make a bomb
 

kwik_uk

Petty Officer 2nd Class
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May 25, 2011
Messages
155
Why not fix rhe mechanical pump, adding an electric pump is a good way to make a bomb

Hi Scott,

Sorry, I don’t quite follow? There’s nothing wrong with my setup at the moment (other than the bulb can be a bit hard on very cold days).

I wanted to add an electric priming pump for no other reason than convenience.

What you said about it being dangerous - how so? Did you mean that pump I listed in particular, or the concept itself?

Like I say, I was only going to do this for convenience, however if it’s going to be dangerous, then I’d rather leave the status quo well alone!
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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any time you add an electric fuel pump to a motor, you need to wire in safety relays so it only runs when the motor is running or cranking.

on an I/O, normally there is an oil pressure switch, or the fuel pump only gets power from the alternator prior to a diode so that it only provides power when the motor runs. during cranking, the fuel pump also gets a priming signal from the starter R terminal.

othewise the fuel pump can potentially keep running and you would have fuel in areas where you dont want fuel making a bomb.

the other issue you have, is your needle and seat on outboards are not intended to withstand the pressure of an electric fuel pump, so you will be forcing fuel out of the carbs into areas you dont want.

while you are thinking convenience, you are actually creating a hazardous set of circumstances.

also, the fuel pump you chosen is not marine rated. if it leaks in a car, the bottom of a car is open and the car is usually moving so no fuel vapors build up. when it sparks, there would not be a dangerous build up of fuel vapor.

however a boat is not an open bottom automobile. its a floating catch pan for fuel that will hold dangerous levels of fuel vapor. so the non-marine fuel pump which has now pushed fuel out your carbs and boom.....

have you ever wondered why OEM's never put an electric fuel pump on an outboard with carbs?
 

JimS123

Fleet Admiral
Joined
Jul 27, 2007
Messages
7,952
I prime in Spring and never have to do it again ALLLLLL Summer long.

If you need to prime more often, somting is wong.

If your primer bulb is hard, you need a new bulb. With age and UV they only last a few years at best.

Your plan is asking for a monumental explosion.

(sounds like the replies are unanimous.)
 

GA_Boater

Honorary Moderator Emeritus
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May 24, 2011
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49,038
I think Kwik is planning on using a momentary switch or should be, so he pushes it to run the e-pump until the carb bowls are filled and releases the switch. A constantly running e-pump is asking for trouble

BTW - The switch you linked to is the wrong type of switch. It's on until you push it to off. Some of these would work, push to turn on and release for off - Like a horn switch. https://www.ebay.co.uk/sch/i.html?_...tary.TRS0&_nkw=momentary+switch&_sacat=107059

But why do you need an e-pump? Is the bulb too hard, takes too long or something else?
 

kwik_uk

Petty Officer 2nd Class
Joined
May 25, 2011
Messages
155
I prime in Spring and never have to do it again ALLLLLL Summer long.

If you need to prime more often, somting is wong.

If your primer bulb is hard, you need a new bulb. With age and UV they only last a few years at best.

Your plan is asking for a monumental explosion.

(sounds like the replies are unanimous.)

I have arthritis (bit crap as I’ve had it 10 years). It makes priming hard even on a new bulb, and I’ve tried many.

I’d use a marine pump, and a push-to make switch. The other pics were for example only. So a 1-2 sec “toot” on a low pressure pump should be fine? It would be isolated using a heat sensing cutoff in line.

sound plausible?
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,590
This will not work as the fuel pump on engine is not strong enough to pull thru the electric one when its off. You have to use a bypass with check valve to do want you want...
 

Fed

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Apr 1, 2010
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I've found OMC bulbs are much softer than old Merc/Mariner ones.
 

JimS123

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Jul 27, 2007
Messages
7,952
I have arthritis

sound plausible?

No. If it were a good idea someone would be marketing a "kit" to do just that.

Buy a soft OMC bulb, add a few extra feet to the fuel line so it can be located on a flat surface, and then simply put your knee on it to pump it up.
 
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