Old vs new design fuel pump? Merc 120 supplier that wont break the bank?

[ianbword]

Im in the market for a fuel pump for my 86 Merc 120 =. Ive noticed an old style and new style. There seems to be roughly $100 difference between the two. Im not brave enough to rebuild a fuel pump lol.

This one is mine...any advice on a trustworthy reasonably priced supplier?

 

[Bt Doctur]

Doubtful you will even find a kit

 

[Scott06]

I think this is it https://www.iboats.com/shop/sierra-fuel-pump-18-7278.html

 

[ianbword]

Thanks for the link...do these pumps have a internal filter that you should change regularly??

http://www.mercruiserparts.com/bam/subassembly/30885/963/110

1	86234A4	PUMP ASSEMBLY, Fuel		NLA		$0.00	$0.00	1
2	49089A1	--DIAPHRAGM KIT, FUEL PUMP		ACT		$60.00	$55.51	1
3	35-49088Q2	--FILTER, FUEL - FUEL PUMP	49088	SS/ACT		$13.58	$13.34	1

 

[thumpar]

There is a filter in the top portion on the pump you pictured.

 

[ianbword]

There is a filter in the top portion on the pump you pictured.

Ahhh okay had no idea this pump is serviceable. Im gonna check on mine before replacing the entire pump, fingers crossed.

If anyone else needs to know how to change the filter even though it seems pretty straight forward heres a link...
https://www.youtube.com/watch?v=x9x9S72qXlo

Luckily mine is facing up so it should be really easy.

 

[Bondo]

Luckily mine is facing up so it should be really easy.

Ayuh,.... Welcome Aboard,...... I prefer the opposite myself,....

You can change it without dumpin' it's gas into the bilge,.....
The bowel acts as a water separator, 'n you can inspect the ounce of gas, 'n debris in it,....

 

[biggjimm]

Agree with Bondo. That looks like the same pump as my old 140 & it was not a serviceable part. I replaced it with the one that has the bowl on the bottom. No more fuel dumping in the bilge when inspecting or replacing filter.

 

[ianbword]

Agree with Bondo. That looks like the same pump as my old 140 & it was not a serviceable part. I replaced it with the one that has the bowl on the bottom. No more fuel dumping in the bilge when inspecting or replacing filter.

So you can interchange between the two? You have any issues with the hard line or the arm being different?

 

[ianbword]

Ayuh,.... Welcome Aboard,...... I prefer the opposite myself,....

You can change it without dumpin' it's gas into the bilge,.....
The bowel acts as a water separator, 'n you can inspect the ounce of gas, 'n debris in it,....

Very good point. Im gonna take mine apart for the hell of it as im not getting fuel out of the pump, and maybe try changing the filter if its dirty. Worst case ill order the other style as I didnt know you could switch between the two.

 

[BudL1te]

I have a Mercruiser 120, it is a 1972. I just ordered a mechanical fuel pump for a 72 Chevy II . A couple of hose clamps, and some fuel line, an inline fuel filter, and I was back in business. I also added a shut off valve two. So I can run the gas out of the carburetor at the end of the season.

 

[Bondo]

I have a Mercruiser 120, it is a 1972. I just ordered a mechanical fuel pump for a 72 Chevy II . A couple of hose clamps, and some fuel line, an inline fuel filter, and I was back in business. I also added a shut off valve two. So I can run the gas out of the carburetor at the end of the season.

Ayuh,.... 'n you created a Bomb, by usin' an automotive fuel pump on a boat motor, in an enclosed motorbox,.....

 

[thumpar]

I have a Mercruiser 120, it is a 1972. I just ordered a mechanical fuel pump for a 72 Chevy II . A couple of hose clamps, and some fuel line, an inline fuel filter, and I was back in business. I also added a shut off valve two. So I can run the gas out of the carburetor at the end of the season.

That pump you put on has none of the safety features of a marine fuel pump. There are some parts that you can use auto parts on. The fuel pump is not one of them. Was the fuel line you added even A1?

 

[BudL1te]

I used good fuel line. Might not be a "Marine" fuel pump, but it is working well and has for the last 3 years. There was not a whole lot of "Safety features" in 1972. A Mechanical pump is a pump and works in the same manner for marine or vehicle. Granted, the marine pump had the filter and at one point in it's life I am sure my old one had screw in lines vs clamps. For my budget, and parts availability in my area, it works well for me. As they are difficult to procure, someone on this site recommended It to me and enabled me to get out on the water. It was that or an electric fuel pump but because of the age of the carbs, pressure output etc, I opted for mechanical and used what was at hand.

Of course, you are correct, it is not the same and should not be considered as such.

 

[hoowahfun]

I used good fuel line. Might not be a "Marine" fuel pump, but it is working well and has for the last 3 years. There was not a whole lot of "Safety features" in 1972. A Mechanical pump is a pump and works in the same manner for marine or vehicle. Granted, the marine pump had the filter and at one point in it's life I am sure my old one had screw in lines vs clamps. For my budget, and parts availability in my area, it works well for me. As they are difficult to procure, someone on this site recommended It to me and enabled me to get out on the water. It was that or an electric fuel pump but because of the age of the carbs, pressure output etc, I opted for mechanical and used what was at hand.

Of course, you are correct, it is not the same and should not be considered as such.

They are constructed differently for a reason. The marine pump has an extra diaphragm to keep fuel from dumping into the bilge when the first one fails. An auto one doesn't so the gas/fumes have a chance to flow out into the bilge and ignite and blow up your boat and kill everyone on board. When a marine pump fails, the gas is siphoned up through the carb and floods the engine so you can't continue to run it like that.

This is a serious life and safety issue that no amount of cost saving is worth.

 

[Scott06]

X2 in the photo in first post you can see a tug on tube coming off the pump. If the diaphragm ruptures this dumps the fuel into the carb vs in the bilge. In an automotive application the gas can drip on the ground no issue. Bulge being enclosed there no where for the vapors to go

 

[BudL1te]

Oddly enough, My old original one was leaking from the filter to pump housing, into the bilge. The one I replaced it with was a sealed unit so I am not sure how a blown diaphragm will cause it to leak gas externally as it does not even do that with an automobile when they go bad???? (Unless defective)

As the carb has a float that controls the amount of fuel in the bowl, and the jets control the amount of fuel into the throttle body I am having trouble picturing how a second diaphragm would work the same as the first in it's delivery yet flood the engine. This in itself would cause dangerous fumes in the engine compartment I would think..

I am not a marine mechanic obviously but I don't follow the description you gave with how a carb works.

Perhaps the "Second" diaphragm just keeps the fumes from the tank, should it be under pressure from being forced through the throttle body and accumulating in the compartment?

I am not arguing the benefits of Marine/vs Auto as your safety point are very valid. At the time I was looking, and the choices available to me I preferred the auto mechanical over the Electrical.

 

[BudL1te]

Thank you for letting me know the specifics. I am in the market for a new Mechanical fuel pump for my 5.7 and I believe I will spring for the Marine one now.

 

[Bondo]

Oddly enough, My old original one was leaking from the filter to pump housing, into the bilge. The one I replaced it with was a sealed unit so I am not sure how a blown diaphragm will cause it to leak gas externally as it does not even do that with an automobile when they go bad???? (Unless defective)

Ayuh,...... A diaphragm pump, can't pump unless the backside of the diaphragm is Vented,.....

If you look on the sealed unit you bought, you'll see a vent hole in it,.....
If the diaphragm fails,.... gas is dumped on the ground in a car,..... or the bilge in a boat,.....

A Marine pump has a fittin' in that vent hole, with tygon tubin' runnin' up to the top of the carb, or the flame arrester,....
If the diaphragm fails, gas is pushed up the tygon tubin', down the throat of the carb, causin' a rich condition,....
Nothin' to do with the needle valve, nor float,....

As I said, you've built a Bomb,....

 

[thumpar]

Even in 1972 then knew a few simple things like fuel and vapor in the bilge makes for a bomb. It has the features like talked about. The fuel line is also supposed to be a solid line on those. They now use A1 on some newer stuff. When the sheriff has inspected me they have mentioned why they check for things and that they have seen them blow before.