Mercury 15hp 2 Stroke

[neil.mccrirrick]

Thanks. I’ll have a read. I’ll photo the part when I get back to the harbour. Blowing up now so may be tomorrow

[neil.mccrirrick]

Hmm I had the same thoughts re the paper gasket over the rubber gasket on the carb body. I did check it to make sure it didn’t block anything and fit it although there wasn’t one there before.

Did you fit yours in the end? Maybe I need to take it off and not use that?

[TmMorris]

Is it dying in the same way it does when you disconnect the fuel tank and run it dry?

Does it then restart and run on idle but not rev or is there a wait before it will restart at all?

Does pulling the choke as it starts to die make any difference?

[Fenlander]

How frustrating. Yes in the end I decided to fit the paper gasket.

[Fenlander]

>>>The only place I had doubt is the cover that is marked top. There is a cut out here which matches with the gasket however when the the cover is tight there is a gap between the cover and carb body by design. Seems to me this will let air in?

The top plate should be flat and seal against the carb body except for that channel that's cast into the carb body to allow air in by design. Is this the gap you refer to or doesn't the top plate sit flat to the carb and are there further gaps?

[neil.mccrirrick]

It does sit flat but I wondered if the new gasket covered all parts of the channel it should. The old one was torn when I took it off so I couldn’t compare

[neil.mccrirrick]

It dies quickly and requires a wait to restart. Find get a great deal of time to check things before the heavens opened. It was fine in the tank at home but obviously I can’t put it under load there.

Raining a lot now so can’t really get back to it. Just ordered a new fuel line and bulb. I dint think it’s that but having a spare is no bad thing. I’ll disconnect to fuel as soon as I can snd see if that changes anything.

I’ll also check the fuel filter to see if it’s full of fuel when it dies as well [emoji106]

[TmMorris]

It sounds like fuel starvation one way or another. It's just working out whether the mix going lean on throttle is due to insufficient fuel flow or excess air being sucked in through a leak as the vacuum increases.

If the latter you might be able to hear it by using a short length of hose and moving it around to note if you can pick up a hiss?

The fact that you have to wait to restart after the stall does suggest a fuel feed issue

[neil.mccrirrick]

On it now briefly as the rain is back. Started first pull then died now won’t start at all. Fuel filter is full. I can pump the bulb hard and see fuel enter the carb until the bulb goes hard. Fuel pump feels like it’s adding fuel when I press the button.

Think I need to take the carb off again. Very frustrating as it was running. I’ll strip and rebuild again and this time try without the gasket between the carburettor and engine

[TmMorris]

Are the plugs wet or mucky?

I'm guessing you have a plastic float pot on the carb and can see the fuel in there and the float working?

If you can see the fuel in the float chamber then that suggests you have fuel supply to that point which would narrow it down to fuel supply around the needle area or excess air from a leak around that point.

If it's not starting now then could that just be flooding and the plugs fouled?

[neil.mccrirrick]

Plugs are wet and about the right colour at light tan. I’d Exocet then to be wet though as I’ve choked it a few times trying to start.

I’ll dry the plugs and strip the carb and fuel pump again as soon as I get chance.

I’ll be back with an update [emoji106]. Thanks

[TmMorris]

https://youtu.be/SshXK8Ehm74

I found this video when trying to get a strimmer running. It's based on those little garden tool carbs but is a really good list of starting points.

[neil.mccrirrick]

Thanks for this I’ll watch it for clues. Just took a video of the carburettor. When I pump the bulb fuel will appear as per the clip until it’s shut off by the float.

Is this normal or is the body worn? Seems odd it will allow fuel into the carb body

https://youtube.com/shorts/BWvgKGfFT9k?feature=share

[TmMorris]

Good question.

The system is designed so that priming the fuel line bulb will fill the float pot so fuel should be able to be manually pumped from tank through the diaphragm pump into the float pot and I guess that until the float rises to close the valve into the jets then fuel can flow through to the venturi.

What you're seeing is what I think you'd expect to see if the float or valve weren't there. What I don't know is whether the float should be closing that valve quicker so that you don't get that flood of fuel.

It's quite a lot of fuel, looks enough to flood the engine to hamper starting. Possibly the float not floating enough.

But, I can't quite compute why that would cause the engine to bog down on throttle. A sticky float often gives a bad idle and leads to flooding on throttle if stuck open or bogging down on throttle if stuck closed.

When you cleaned the carb did you test the float for floatiness? Or smooth action in situe and that the valve was being opened and closed?

[TmMorris]

Also, the guy who did the video I linked to above has a range of videos that I've found really useful as he uses simple English and pretty pictures. They're great idiots guides.

[neil.mccrirrick]

No did a visual check of the float no imperfections and I shook it no fluid inside. The valve moved freely. Nothing there to make me think anything was amiss. Raining again and I’ve no garage here. As soon as I get chance I’ll strip it down again and hopefully something will pop out

All that petrol does explain what I would see in the sea from time to time. Not a great design for the environment but it’s old and I guess wasn’t an issue then

[TmMorris]

At least we can see that the main jet looks clear.

A random thought is how lean you have set the idle? That jet still has an impact on high Rev running but am I right in recalling that the engine doesn't bog down immediately on throttle but after a short while, as if the fuel in the carb is getting used but then not replenished appropriately?

[Lemonbonbon]

Is air getting in at the junction between the float chamber and the main body. ie is that seal good with a new gasket

[neil.mccrirrick]

Carb and fuel pump stripped and rebuilt. It won’t start unless the mixture screw is out 2 and a half turns. I have put the paper gasket between the carb and reed throat back on.

I think I might take that off and see if there is any change.

It will start now with some reluctance but cuts out almost straightaway

[neil.mccrirrick]

In the first picture this is the part of the carb that allows air in. The new gasket doesn’t seem like a good fit so I wonder if too much air is getting on there? The cut out has to go over the channel but it’s a little oversized.

Could well be a complete red herring that though