Faultfinding on mariner 2.5 outboard

conolan

conolan

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My Mariner 2.5hp outboard, 4 years old has stopped working. Won't fire, but it was firing happily a few weeks ago. I've done the following.

1. Checked that fuel is coming from the tank to the carb
2. Checked that the kill cord switch works (used multimeter)
3. Checked and cleaned the spark plug.

How can I tell if spark plug is getting voltage
Any other things I can check.
 
With the ignition lead connected to the spark plug, short the screw on the plug to any ground point on the engine, pull the cord and look for a spark, hold it with insulated dry pliers if you dont want a shock :)
 
arthurbeer said:
With the ignition lead connected to the spark plug, short the screw on the plug to any ground point on the engine, pull the cord and look for a spark, hold it with insulated dry pliers if you dont want a shock :)
Click to expand...

That worked, wife saw the spark. Now what?
The spark plug is wet, so fuel must be reaching it. Plug is clean also, and I narrowed the gap a little in case that was a problem.
 
Once it has failed to fire and the plug is "wet", you need to clean the plug and dry it off. Try to start again. If you have another, suitable plug available I would try that. Two strokes are very sensitive to the condition of the plug. A motor-bike trick that used to work for me was to remove the plug, pop it into a hot oven and after a few minutes put it back quickly into the head and try to start the engine. Before doing anything more drastic, I would then buy a new plug and try that.
Good luck.
Morgan
 
Hmm... Im not a mechanic and dont know specifics about outboards, im sure someone will, what I know is only generic engine knowlegde, but considering a lawnmower engine is not all that different...

If the spark plug is wet, sounds like the engine is flooded. Let it drain out then retry the engine.

If not check the throttle isnt stuck open allowing to much fuel in.

If you have a compression tester get that on it but im unsure how likely it'll be that.

Other than that lets hope someone will be along soon with the answer
 
You dont say what the spark was like. You should be able to get a good bright blue spark that will jump 3/8" from the lead when disconnected from the plug.

Replace the plug with a correctly gapped new one.

But pull the engine over several times on the starter to expel excess fuel before fitting the new plug.

The professionals would do a compression test.

Any chance that the carb is flooding due to a defective float or needle valve?
I assume it has an integral tank therefore might try allowing the carb to fill and then shutting the fuel tap again.
 
I have a mariner 2.5 I'm guessing yours is similar to mine. (left slider for throttle, right slider for choke.. Instant drive with no reverse gear)

I'd certainly go along with VICS advice and change the plug for a new one with the correct gap. (They are peanuts and a good starting point)

Also, are you trying to start it full choke? Sometimes mine doesn't need full choke and only floods it if I do.

With the new plug, i'd try starting with no choke then gradually increasing the choke and trying again.

If you flood it, you need to leave the motor for 30 seconds or so before retrying.
 
If you're getting a good spark then look at your carb. I had problems with mine this year after leaving it on the pushpit all winter, with the fuel tap off. the fuel evaporated and salt water got in. The needle valve became corroded and kept getting stuck either open (flooding) or closed (starvation). Both meant the damn thing wouldn't fire. Luckily Cap'n Slarty (once of this parish) had a spare carb from a 3.5hp that I was able to fit and it now starts at a half-pull. more power too.......

So give you carb a good clean and check that the needle valve is working correctly.

Cheers,

C.
 
People will throw their hands up in horror, but the way to decide if it's carb or sparks is to remove the covers, pour a tad of fuel in the carb throat and start it. If it runs the carb is the problem, if it doesn't it's probably the spark.
As others have said, use a new or heated plug to do this.
It's only the same as you do when when you start your lawnmover or leaf blower. That little bulb you press squirts neat fuel into the carb throat. These are simple little motors, give them fuel and a spark and they'll run.

tohatsurepaired1.jpg
 
People will throw their hands up in horror, .
Click to expand...
Standard recommended practice. Preferred to using starting fluid in a 2 stroke.

In this instance though, since the plug comes out wet with fuel i wonder if there is anything to be gained ... worth a try though I suppose
 
Age of petrol

usual thing if engine been standing over winter, fuel looses its umph. Try some new petrol. Having said that, just ran my suzuki 3.5 for 20 minutes in the tub, then when I got down to the boat, engine fired for about 20 secs then stopped - and then refused to start again - 1 mile row, fortunately with the wind!!
 
firstly, get a new plug, they can often appear to be sparking when in the open air, but do not spark correctly when under compression (spark leaks round the side)

secondly, empty all the fuel and get some new fuel.

if that doesnt work, try starting it on low throttle and no choke, using a squirt of some "easy start" from a can from halfords if it runs on that but not for long, then your carb is clogged with old 2 stroke oil, easy, take it off, clean in neat fuel.
 
Check whether you have been turning on the fuel tap before opening the vent cap. You need to open the vent first, then the fuel tap. A build up of pressure in the tank can cause the fuel to flood the carb if you turn on the fuel first.

I had the same problem with a Tohatsu 3.5hp, but this simple routine + minimal throttle and zero choke make for easy starting.

Also spiced up the fule last year by going for a high octane fuel.

Good luck!
 
Sy-Revolution said:
Easy Start - AKA Car smack, watch out, they get addicted to it!
Click to expand...
Ok someone has to take the bait. How can a lump of mechanical gubbins get addicted to anything?

It's bad for two strokes because it contains no oil.
It's bad for diesels too because you have no control over the ignition timing.
It's dangerous on (diesel) engines with manifold heaters.
 
On a slightly optimistic note, once you get it running ok, it shouldn't be too fussy about starting techniques other than not too much choke.

After giving the carb a good clean out and new fuel in the tank plus a new plug, mine starts between one and half a dozen pulls regularly. Regardless of the order of opening vents / fuel tap etc.

Only thing to be careful is not to go too mad on the choke. At the moment I try a couple of pulls on mid choke before increasing. In mid summer, I try with no choke first.

Rarely, outside the depths of winter, does my outboard require full choke to start.
 
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