Mercury 15hp 2 Stroke

[Lemonbonbon]

Is this worth a punt only £18

https://www.ebay.co.uk/itm/255352886...8AAOSwVQJhQa1O

[neil.mccrirrick]

Thanks ordered one really to see if the top gasket is deformed. Been reading more about this it seems it might be possible to put the float in incorrectly?

It seated ok and it does allow the fuel bulb to go hard but I’m not happy about all the fuel that sprays out before the bulb goes hard.

I’m wondering if this is where the leak is as the bowl empties its drawing air or too much fuel.

Think I’ll take it off again and see if the float can go in different positions. I definitely pushed it close before placing the bottom on snd screwing in the jet and it seated but maybe something there?

[The Gurnard]

Hi Neil.. Im not around much just now as too busy boating to get involved with forums...

It looks the same carb as I rebuilt last year and have cleaned several times on my Mariner 25HP two stroke. I had no issues but followed videos like this one to keep me right

https://www.youtube.com/watch?v=_skDBg4FALk

I kept the old parts and also have the full manual for the 25HP version so if you still have bother I can perhaps assist if you bring the OB to Maximus next time you are there and I will call round. Hope that helps.

Im getting rid of my 25HP two stroke today and collecting the new Yamaha 25HP 4 stroke..its now arrived ...yeah ...so have a few spares and some oil you may be able to use.

[neil.mccrirrick]

Thanks Donny very much appreciated I'll keep plugging away but I will let you know how it goes. Hope all is well speak soon

Best Neil

[TmMorris]

I think the fact that when you prime the fuel you're getting fuel washing into the Venturi isn't meant to happen. That looked like a lot of fuel that would simply flood the engine preventing it from starting.

[Fenlander]

This is all very weird.

My initial gut feeling was a simple but elusive blockage somewhere in the carb/fuel pump causing fuel starvation at anything much above idle. But the fuel spurting up in the video attached to post #33 does, as TM says, look as if the float is not closing properly. The float should shut off fuel before it spurts up like that. Also I'd not really taken in you commented a couple of times that pumping the fuel line bulb while running will stop it??

So could it be you have a sticky float that is both reluctant to close on initial priming and sticking closed in running causing fuel starvation??

As an aside in the past to help prove a fuel starvation issue I've rigged up a small amount of fuel in a container above the outboard piped directly to the carb so there is a gentle gravity feed. It cold be this would show up a float issue as without the fierce pulse of the primer bulb being pumped if the fuel just runs through into the carb throat without stopping it proves there is a problem with the float.

Just a final thought for now... have you checked the float height setting?

[TmMorris]

Those were the lines I was pondering the other day. On idle it's as if the float isn't closing the valve so flooding can happen but on wot it's as if it's not opening to let fuel through.

If it's one single issue then a sticky float might be the reason. But it's always possible that you've got more than one issue such as a float with insufficient buoyancy or not closing the valve while at the other end of the carb an imperfect air seal to the crank that's replicating fuel starvation on revs.

It could even be that the float issue, if there is one, wasn't part of the original issue but has materialised during a rebuild?

If I think back to my carb dismantling efforts would I be right in recalling that there is a vertical pin that can come out when removing the float? Is that pin the valve stem that is moved up and down by the float action to open and close the fuel feed to the carb? Is it plausible that the float is working perfectly but there is no valve being closed if that pin is missing?

[TmMorris]

Duplicate

[Fenlander]

This isn't a perfect video but does show quite well the float arrangement on these Mercury carb types. So yes the needle isn't attached to anything when the carb is dismantled but unlikely Neil has left it out and anyway had he done so the fuel would never stop gushing when the primer bulb was pumped.

I'm guessing this will be a rubber tipper needle. I usually replace them on a full carb overhaul and put a little Brasso on a cotton bud to polish the alloy or brass needle seat. The other thing to watch out for that is mentioned in the video is that the brass arms that rest on the float do not bottom out on the carb body before the float needle is able to firmly close.

Also with this round float type that is free riding up and down the alloy jet housing there is the potential for it to twist and bind particularly if there is wear on the "splines" on the inside of the float. The brass arms that operate the needle should be evenly set so when the needle has closed the float sits evenly on the central casting not twisted. I prefer the floats that hinge on a brass pin so are kept in mechanical alignment rather than freely bobbing around.

https://www.youtube.com/watch?v=FmRS9AhC5KI

[neil.mccrirrick]

Thanks chaps all good points. The metal piece is definitely in place but not replaced as I have no replacement. It does seal eventually when the bulb is hard so hopefully it’s ok it’s more the float isn’t coming up with the fuel quickly enough to seal it off ?

I’ll strip the carb again and check the float. I know the arms were level but perhaps the float isn’t seated well?

As far as I know you can’t adjust float height on this model?

We’ve family round now got two days so probably won’t be able to get back on it until they leave.

I’ve predate new fuel line and bulb,(the one on it is less than 12 months old but outside all the time)

I’ll change that out, check the float, and take off the paper gasket to the reed valves next to see if that resolves anything?

It’s very perplexing cleaned out two 6hp Suzuki systems last week all start first pull now, I say that just so you have some confidence I think I know what I’m doing [emoji1]

[neil.mccrirrick]

Sorry about the weird words. On my phone and predictive text is not helping [emoji1]

[Fenlander]

You set the float height by bending the brass arms that operate the needle.

[Locozodiac]

If the carb was spotless cleaned and well assembled, when the motor dies at wot after been running strong for some time, when it's restarted after has cooled down for some minutes, does the motor restarts immediately and runs strong till finally dies at wot after some minutes run ? f so could have an electrical component heating up. shorting till cools down. Install 2 new NGK B7HS / BR7HS spark plugs well gapped to 1.0 mm as a starter. BTW, how old is that motor ?

Happy Boating

[neil.mccrirrick]

Think I may have cracked it. The gasket that sits under the cover marked top is creating a problem.

If I take that gasket off and manually pump petrol no fuel comes up the Venturi from the bowl. In other words the float works as it should and seals the fuel off no leaks.

If I put the cover and gasket back on it leaks like a sieve.

It’s a new gasket but looked a little oversized to me when I put it on, it’s latex the old one was card but ripped coming off.

So I’ve cut a new one from the old fuel pump gasket while I wait for a new gasket set to turn up.

Raining again so I can’t fit the bodge yet to test this out.

Still confused as to why it will pump and not leak with no cover on but leaks with one on?

[neil.mccrirrick]

For clarity the gasket goes over the part of the carb in the first picture I posted here

[neil.mccrirrick]

The bodge is in. No fuel in the Venturi now snd the engine starts [emoji106]. Still won’t rev but I bent the bracket on the float slightly earlier thinking it may be float height as fenlander suggested

When the new gasket arrives I’ll take it off again and see if I can bend it back.

Progress at least. Thanks all for suggestions etc all helped not least with my sanity. I’ll update again when I’ve hopefully got it running properly

[neil.mccrirrick]

Nearly fixed now. Took the bodge off and cut a new gasket using card. Took the bowl off and as far as I can tell bent the float arms back to where they were

Starts first pull now. No leaking fuel and will rev in the tank. I’ll get it in the water this week to load test

Seems to me that the top part of the carb needs air in to allow the Venturi to work. If ut does not seal fuel will come up the sides of the Venturi and flood the carb and all the problems in this thread ensue

I suspect dying at wot is all linked. Once I test in the water I’ll update this again in the event someone else has the same issue.

Proper head scratcher [emoji1]

[neil.mccrirrick]

All good now starts first pull up to wot with no hesitation and ticking over nicely.

Summary is ………, bloody boats [emoji23][emoji106]

[TmMorris]

Excellent.

[The Gurnard]

Great you got it sorted Neil . Just be glad it wasn’t a big engine..this one was parked just up the road from you today and I bet you wouldn’t like to clean its carb out. Was quite bumpy south of Kerrera this morning, I almost called in to see you today