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Old 20 April 2015, 14:17   #1
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Mariner 15 2-stroke carb and fuel pump overhaul.

Following on from the thread where I took the carb off my 2004 Mariner 15 2-stroke to investigate fuel "spitting" due to perished breather/balance hoses I thought as it was off I might as well get an overhaul kit.

Well actually at first thought I might as well just do the fuel pump diaphragm which should have cost about 6 looking at comparable ones for other outboard types online... but Mercury only supply them as part of a full carb gasket/overhaul kit for this model outboard... so that cost me about 55!!

Appreciated Max's referral to Black Dog Marine for parts... they and Pacer Marine on Ebay were close to the same price. However postage was free with Pacer Marine but Black Dog relate their postage to item price and there was no way I was paying over 7 postage for a small light Jiffy package that in reality would have been about 1 to send. Pacer Marine's service was first class with same day dispatch and quick postage. Sent the right part too which always helps!

So the gasket/overhaul kit arrived this morning...
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Old 20 April 2015, 14:22   #2
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You get all the gaskets for the carb and fuel pump plus the fuel pump diaphragm and the starting primer pump diaphragm on the blue rod with its top seal, bottom plug and small spring.

Annoyingly there were 2 gaskets and a light rubber diaphragm that don't seem to suit anywhere on my carb. Annoying as it seems 3 of the approx 10 items weren't for my model and I'd rather they were left out and a 17 discount applied!
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Old 20 April 2015, 14:28   #3
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So I got to it and took the fuel pump and very simple carb apart. I was really pleased to see the float bowl hadn't a spot of dirt or corrosion in the bottom (see image, before it was cleaned). The rest of the carb innards were just as clean.
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Old 20 April 2015, 16:10   #4
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Just a tip, but a common mistake, make sure that you fit the correct carb flange gasket when you refit the carb.
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Old 20 April 2015, 16:20   #5
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Mine's an odd one. There is a paper gasket in the set that matches the reed side of the main carb flange but there wasn't one fitted. Mine has a rubber straggly shaped O-ring thing that appears to be bonded to the carb side of the reed block where the carb bolts on. Thankfully that is in perfect condition.

There is also a second gasket in the set that 90% fits the carb flange but it fails to correctly allow for the offtake for the vac/balancing hoses and would cause an air leak if fitted.

I'll do some pics in a moment.

Just a few comments on what I found with the carb once stripped...

As mentioned above it was pleasingly clean but it will get a good squirt of carb cleaner in all the jets/orifices. The fuel pump diaphragm was not too bad but probably original so no harm in swapping it out after 11yrs. The starting primer diaphragm was hardened and would probably have split before too long... also its rubber at the top where the blue plunger comes out was hardened almost like plastic so not providing a proper seal (both of these parts were in the kit).

One big mistake I only just avoided. When you take the bottom plug out from the primer chamber there is a spring and tiny ball. You get a replacement spring in the kit but not the ball and it was only by chance I saw the ball as it rolled across the bench heading for workshop oblivion.

Slightly blurry pic of the ball...
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Old 20 April 2015, 17:01   #6
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Thanks Al for making me look at this again.

So here is a picture of that odd straggly O-ring type seal which looks bonded to the reed block flange and is the only seal I originally had between that and the carb flange.

Also a picture of a paper gasket in the set (one I thought was spare) put into that position and it does have all the required shape and cut-outs etc.

Also same gasket put against carb flange and it again would work fine.

But why didn't I have any paper gasket when I took it apart... and should the paper one be used in addition to the rubber one when you do a carb refit??
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Old 20 April 2015, 17:05   #7
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And here is another spare gasket that was in the set which initially looks a good match for the carb flange but note it would not seal all round the area where the small brass stub offtake is.

Might this be the "incorrect" gasket you might use by mistake??
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Old 21 April 2015, 00:34   #8
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Manufacturer gaskets are a licence to print money. Having said that - they're money well spent for resolving numerous issues with vacuum, pump, fuel, combustion, etc.

I'd have thought that paper gasket should be applied over the embedded rubber seal. Suspect who ever had the engine before didn't use it at strip down. They probably looked up the price of gaskets!
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Old 21 April 2015, 02:41   #9
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I've made my own (a set of different half a dozen mixed thickness gasket paper is only a few on eBay) for simple templates like the thermostat but that one is a bit tricky to cut at home...
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Old 21 April 2015, 03:28   #10
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>>>Manufacturer gaskets are a licence to print money. Having said that - they're money well spent for resolving numerous issues with vacuum, pump, fuel, combustion, etc.


Yes that's where they get you. Seems a lot of dosh so you think do I really need them... then you think of possible running issues in the middle of a 2wk holiday on the Scottish west coast so you can't not get the proper set.

At the moment I'm inclined to fit the paper carb-reed block gasket as it would add to the sealing if the carb flange isn't totally flat which can happen over time with bolted down alloy flanges.

Like you Max I always had gasket paper to hand for stat housings and similar, particularly as we spent some 20ys running 20-40yr old tractors. Everything was a good size on them and a scalpel plus hole punches for the stud holes sorted many gaskets to save buying.

Max when you get home tonight is your Mercury easy to access and have a look if you have that paper gasket between carb & reed block? It would be obvious if you have as it is slightly larger than the flanges in places and you would see the edges. Only if it's no trouble.
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