What’s the problem?

andy01842

andy01842

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I have a 4hp 4 stroke Mariner outboard brought it new 3 years ago, it has run for about 30 hours. This year it has started to give me grief. It always starts 1st pull 2 pulls max and ticks over perfectly. Drop it into gear open the throttle a bit and away we go great, smooth and quite no problem, however a bit more throttle and it starts to misfire a bit more throttle and it cuts out and stops, a gentle pull on the cord and it starts and ticks over lovely. A bit of jiggling with the choke and it will run up to flat out push the choke in and it stops. So it got to be a fuel problem, a blocked main jet. I stripped the carb and it is perfect checked the fuel filter etc all in very good condition. I have now fixed the problem but what do you think it was? And no it was not the tank vent. I will post the answer later.

Andy
 
points

if it has one, the fuel cut off

stop button vibration.

several more options to make life difficult.

I wont even suggest stale fuel
 
If the tank vent and carb jets and adjustment are ok then its a restriction in the fuel flow, muck in the tank, fuel line, sticky or blocked needle valve. Defective fuel pump. Or its an air leak in the fuel line or connection to the motor. Pumping the bulb would be a something to try.

If its an integral tank still could be muck in the tank, defective tap, air lock (unlikely) or again the float valve.

Really dont think its ignition as it still would not run on choke. Can't be points or condenser as it's bound to be electronic. Would always check/replace plug as a matter of course.

Big air leak between engine and carb possibly. (very doubtful)
 
[ QUOTE ]
read the post chaps :
------------------------
I stripped the carb and it is perfect checked the fuel filter etc all in very good condition.
------------------------
hint, it's nothing to do with the above !

[/ QUOTE ]

I'm waiting with baited breath - i wish you would stop pissing about and tell us what it is - It's 9 o'clock now, so plenty of time for guesswork /forums/images/graemlins/cool.gif
 
Apologies, missed that /forums/images/graemlins/blush.gif

if it can be coaxed to full revs with the choke on, then it's not fuel supply, or that wouldn't happen.

It sounds more like an Air leak in the induction system then, which the surplus of fuel supplied by the choke balances out.

Inlet manifold gasket perchance?
 
Big air leak between engine and carb possibly. (very doubtful)

.................................................................................

Check the carb is sitting on its stub correctly. If similar to a yamaha then it has to be pushed hard home up the stub before clamping otherwise there will be an airleak.
 
The answer!

It was the spark plug which was not very old.
I believe the insulator had a very small crack down inside the plug body. As the throttle was opened and the pressure inside the cylinder increases the voltage from the ignition coil increases to a point where a spark occurs through the crack deep inside the plug instead of at the tip. This spark does not ignite the fuel and the engine stops. A new spark plug fixed my problem. But the crack could be anywhere on the HT side of the ignition system.
Why pulling the choke would let the engine run up to full load I can only think that the extra fuel cooled the plug.
I also have a mercury 4hp 2stroke that is beginning to show the same problem. I will fit a new plug to that to see if that has the same problem.
A long time ago I brought a pair of new plugs for my motor bike. The plugs where the correct grade but a different make than I had used before. It would not start when fitted. I change one new for one of the old plugs, it ran on one cylinder. The new plugs must be duff I thought although a good spark was seen when tested. I gave them to a friend and he ran them for 20,000 miles no problem!
I will now always keep a spare plug and change it at the first sign of trouble. I did not think a plug with so little hours would be the problem. I hope this helps any one with a problem engine.

Andy
 
Re: The answer!

My Honda 4 stroke 2.3Hp will only run with the choke fully out, (would hardly run at all until I changed the spark plug) - which was why I was waiting with baited breath.

Cuts out in any of the following circumstances:

1) choke pushed in even slightly

2) throttle close down completely

3) throttle opened too far

I'm reasonably sure it's not the spark plug.

Cheers

Richard
 
Re: The answer!

That is very likely muck in a jet. Gummy petrol etc. I had exactly the same on the same engine. Strip, clean, change petrol, off you go. /forums/images/graemlins/smile.gif
 
Re: The answer!

I would agree with Gunfleet, also check the fuel filter and the tank vent. Dose the petrol smell off, if the petrol is old throw it and get fresh can make all the difference. Best way to clean jets is with an air line. Poking bits of wire down them can enlarge the hole.
 
Re: The answer!

I'm not that confident of taking it apart and messing with the carb... might be worth £100 or so to have it properly serviced by an official Honda centre in Malta.

havent dared mess with it during the trip as it works well enough, and i dont want to cock things up and lose our lifeline to the shore.
 
Re: The answer!

Blimey, is it still doing that, Richard? I'd take it to the appropriate high priest, who will change the oil, grease it, and mumble the right words over it. I took my Suzuki to one last winter and it came back hugely better.
 
Re: The answer!

Give it a whirl. As long as you don't lose any parts (work on a tarp), even if you get stuck you can still take it to the service engineer. Just tell him it let you down at sea and had to try to get it working.
On the other hand you should be able to fix it. It's not a highly technical job. Just remember to use the correct size screwdriver for the slot in the jet. Otherwise you can chew them up as they are only soft.
 
Re: The answer!

[ QUOTE ]
Blimey, is it still doing that, Richard?

[/ QUOTE ]

I know I like fiddling about with things until I understand them, fix them, or screw them up completely, but this was one of those "If it aint broke dont fix it", things.

I changed the spark plug in Mallorca, and it was immediately better than before. I've also run it to almost empty on a couple of accasions to majke sure there is no old fuel left.

It doesnt really matter that it wont do top speed - and I've got used to shutting it down just before ramming the pontoon or the boat <g>

It has actually got better as time has gone by - it will now run slowly enough for the clutch to cut in and out, which it wouldnt do before - but not with enough consistency to trust it at stopped.

As with a few other things, i'm going to get safe in Malta before risking unnecessary repairs.

Cheers

Richard
 
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