Odd outboard problem - Mariner 4 stroke 2.5 hp

Shuggy

Shuggy

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I have an odd outboard problem that I can't cure and I suppose I'm looking for hints and tips before I throw the towel in and take it to a professional...

It's a two year old Mariner 2.5 hp 4 stroke in VGC (i.e., no corrosion, always stored indoors, flushed through regularly).

I put it in storage in October. Storage is inside the house, so warmish and dry. To prep, I did the following:

> Flushed it through in a dustbin
> Emptied the petrol tank
> Ran it until the carburettor was empty and it stopped
> Cleaned off any salt water with a damp sponge
> Dried it and put it away

At the start of the season I put in fresh fuel. It started after about four pulls and run perfectly for about two minutes ferrying various kit from the pontoon to the boat, and then it cut out. It started again after a couple of pulls but died again quite quickly. It could be persuaded to keep coughing on by rapid moving of the throttle (up and down) but would die again.

I took it home and I've done the following:

> Filled with different fresh fuel (just in case)
> Taken off the carburettor and checked that there's no gunk/dirt/gummed-up fuel in it, cleaning off all parts
> Taken off the in-line internal pipe filter
> Checked the float will, when dropped, allow for a clean flow of fuel from the tank to the bowl (it will)
> Checked that the tank vent is working by blowing back through the fuel pipe (it is)
> Checked that the engine oil level is correct (it is - I don't know if there's a cut-out on this model if there's low oil)

I've still got exactly the same problem. So I've ordered a new spark plug although the existing one looks just fine.

Any ideas? Could it be something electrical overheating? I'm not sure how the ignition works - could a coil pack be faulty?

Thanks...
 
I agree that it does sound like a fuel starvation problem. If it was ignition I think you would smell unburnt fuel.

I think the most likely explanations are that there is still a small grain of sand intermittently blocking the jet or that there is an air lock in the fuel pipe / filter. Have you opened the carb drain and just let fuel flow through from the tank for a while. I sometimes blow hard into the fuel filler to push the fuel through and check it flows freely with no air locks.

No harm in changing the plug as it's a cheap way to rule it out and it's good to have a spare anyway.

Richard
 
the fact of wobbling the throttle enables it to continue running suggests to me fuel blockage in the jets.

did you remove them and clean them and the body with carb cleaner. small engines have v small jet holes so are liable to blockage.

modern petrols have ethanol in them which encourages the shifting of previously stuck dirt, only one place it goes ..... to the jet, along with corroding some aluminum alloys, namely old carburettors.
 
david_bagshaw said:
the fact of wobbling the throttle enables it to continue running suggests to me fuel blockage in the jets.

did you remove them and clean them and the body with carb cleaner. small engines have v small jet holes so are liable to blockage.
Click to expand...

No - I just cleaned them by pushing the wire from a wire brush through all holes. I should buy some carb cleaner and give it all a good soak.
 
Shuggy said:
No - I just cleaned them by pushing the wire from a wire brush through all holes. I should buy some carb cleaner and give it all a good soak.
Click to expand...

Bad way of cleaning jets. They're soft brass, so nothing hard should be shoved up them. Best method is to blow through with an air-line. If you hold them up to the light it should be apparent whether they're blocked.
 
macd said:
Bad way of cleaning jets. They're soft brass, so nothing hard should be shoved up them. Best method is to blow through with an air-line. If you hold them up to the light it should be apparent whether they're blocked.
Click to expand...

As long as the diameter of the wire is smaller than the bore of the jet and an easy sliding fit, it would be OK. Jet cleaning wire easily available. I use guitar strings quite successfully ;)
 
Sounds like a classic 'droplet of water' case.
These small engines have very small jets, which will trap a droplet of water.
Or it could be dirt.
I strip carbs on a clean sheet of white paper, it's amazing what other mechanics leave in there....

A new plug may help. I prefer NGK plugs.
A new plug may just keep the thing alive on a weaker mixture.

A trick that sometimes works on some carbs is to crank the motor with the throttle open but the intake blocked. It can drag water droplets through the jets.
Possibly best done with the plug out.
 
I have recently fixed a similar issue on a Mariner 6hp engine on my Father in Law's boat that would only run with the choke out. I had previously stripped and cleaned the jets with Carb cleaner last year without curing the problem. On the previous occasion I didn't have anything to probe at the jets with. I had another go at it again a few weeks ago. Holding up the main jet to the light I could see through it as previously but noticed it wasn't quite round. I gave it a soaking in carb cleaner again and then gave it a probe with a fine sewing needle. Initially the needle wouldn't go through, but after a bit of prodding it cleared. I re-assembled the engine and it now runs fine. I can only assume the jet was gummed up or something had been dragged into the jet partially blocking it.

A new spark plug may help, they do break down. My past experience of outboard ignition coils is that they either work or they don't. I have never known one to go intermittent.
 
bikerbill said:
As long as the diameter of the wire is smaller than the bore of the jet and an easy sliding fit, it would be OK. Jet cleaning wire easily available. I use guitar strings quite successfully ;)
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Plus one for a piece of wire pulled from a wire brush. Been doing it since I had my first Bantam 50 years ago! No probs!
S
 
Had a prob with a Mercury 3.5 (aka Tohatsu) and the filter in the tube to the carb was not properly located on the fuel tap. And, there was some fibrous stuff that was causing the float valve to stick open. New engine, so this came from the factory.
 
Well, here's the answer. I ordered a new spark plug and fitted it today.

All ills are now cured, so I guess the insulation was breaking down after a couple of mins on high load?

It's running beautifully with no hint of hesitation or cut-out.

Bizarre!
 
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similar problem, removed leg, stripped engine, renewed both seals, whilst out new ring,desalt, new head joint, although 14 she now runs like a 2 year old.

Last use was to get water about 10 minutes, back to boat dropped off H20, 2 minutes to beach for dog and never ran again, did most of the things mentioned as other posts suggest, no go. so bit the bullet and now have a nice little engine again
 
Shuggy said:
Well, here's the answer. I ordered a new spark plug and fitted it today.

All ills are now cured, so I guess the insulation was breaking down after a couple of mins on high load?

It's running beautifully with no hint of hesitation or cut-out.

Bizarre!
Click to expand...

so common.... no logic ..... all the evidence points to carb/ fuel problem but a new plug sorts it.
 
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