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Old 28 February 2016, 06:38   #1
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mercury 15hp stalling help please

dragged my 2005 mercury 15hp 2 stroke out of hibernation yesterday and put it in a barrel of water .it started after about 5 pulls not bad as its been stood for a year nearly. anyway it runs good and after about a couple of mins the stat opens and has a good water jet. but let it idle for more than a couple of mins and the revs start dropping until it cuts out .I tried giving it a little throttle but it just baulks and dies one pump on the primer bulb and the revs pick back up to normal tickover and is good for quite a while but if I give it a rev as its dropping back down to idle it starts to die again once more 1 pump of the bulb sorts it .it had a new fuel pump diaphragm the beginning of the last season it was used .I'm thinking it can only be that or drawing air somewhere on the fuel line (though when I prime it before starting it goes nice and hard if it had a fuel line/primer bulb problem would it still do this) anyone come across this before.any help appreciated
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Old 28 February 2016, 08:37   #2
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Fuel pump diaphragm I would say happened to me with a 25 Suzuki if you have an air leak you will struggle to get a solid build bearbelly
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Old 28 February 2016, 10:33   #3
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The thing I've had on this model is a split in the very small vacuum/balancing hoses that go off the bottom of the carb/manifold area allowing a variable air leak and poor slow speed running/stalling. They often split right where they go to the head/carb interface which is hard to see without a small mirror.
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Old 28 February 2016, 11:08   #4
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I would say because the pumping of the bulb makes it ok again then the pump is not maintaining pressure if you lift the fuel tank higher than the engine to maintain a head you probably will run ok, if you have a hole in the bulb below the non return valve in the bulb fuel might fall back into the tank as another possibility.

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Old 28 February 2016, 11:34   #5
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Agree re pumping Jeff. I've had motors in the past where they would run fine with the tank in the boat and outboard on the transom but with the outboard in a high test bin and the tank on the floor (i.e. a far larger head to pump up) they would not idle well.
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Old 28 February 2016, 11:34   #6
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cheers folks a few things to look into. is there a how to guide anywhere if I have to change the fuel pump diaphragm I haven't done one before. oh and it did this once before in the boat but just a one off now on the trolley in the water bin and the tank on the floor its doing it all the time so that fits with one theory
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Old 28 February 2016, 12:24   #7
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Quote:
Originally Posted by beerbelly View Post
cheers folks a few things to look into. is there a how to guide anywhere if I have to change the fuel pump diaphragm I haven't done one before. oh and it did this once before in the boat but just a one off now on the trolley in the water bin and the tank on the floor its doing it all the time so that fits with one theory
There pretty simple beer belly just strip the old laying the bits in order and the way round they came off when done set the new bits up the same way to check and fit in reverse when you buy the kit it might have a drawing with it.
If you look on eBay you will pick up a service manual for a few quid if stuck.
Cheers
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Old 28 February 2016, 15:56   #8
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Look for Lsailer1 on YouTube Mercury 40 fuel pump refurbish it will probably be the same pump step by step strip down real helpful.
One thing to look for is bits if the diaphragm has perished possibly gone to the carbs
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Old 28 February 2016, 17:34   #9
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OK so not a step by step but there might be something of interest in the images from when I did my carb and fuel pump together. Particularly the left hand image on post #3.

Mariner 15 2-stroke carb and fuel pump overhaul.
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Old 29 February 2016, 16:36   #10
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cheers lads ordered a fuel pump rebuild kit from pacer marine so hopefully by the weekend all will be good .I'm hoping to sell it soon and don't want the new owner to have any problems
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