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Discussion Starter · #1 ·
I started my outboard last night (mariner 75hp 4 stroke non-efi) after full service and servicing the water pump. There was no problem with the water pump and water flowed nicely.

There was however an occasional stumble by the motor. Its hard to describe, I dont know what a misfire sounds like and I dont think it was a misfire, it was just like a cough or a hiccup every so often - only at idle. She did not cut out though.

I am thinking a decent run might clear this and that it could be some old fuel gunged up in the carbs. We did run the outboard out of fuel at the end of the season though.

What can I do to further diagnose this? Or indeed fix it? I am bit loathed to wait until I get the boat back in the water as its a hassle to haul her in and out.

Could it be carb settings or timing that is out?

Thanks as per usual,
Ryan
 

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The problem here is the load/no load characteristics of an engine. Currently you are running it under no load and getting an intermitant mis-fire. Under load this could easily turn into a full blooded mis-fire and cut out. Or just as likely a cough and splutter clearing the tubes so to speak and then perfect running.

To be sure and certain return the boat/engine to the dealer and ask for a engine under load test. The dealer does this by unning the engine with a special device that replaces the prop but simulates full loading.

Or if you dont mind the effort of launch and recovery (which is the way I would go) launch the boat and go for a sea trial but stay within range of easy help if the engine does cut out.

IMHO the second way will turn out fine but do all the obvious things like checking the plug lead seatings and getting rid of any damp under the hood (WD40).

Afishionado
 

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Discussion Starter · #5 ·
When I increased the revs it seemed to run fine - admittedly it was indeed not under load. It would seem to be a fuel issue though.

Ryan
 

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Hi MarieK,
You mentioned that you let the carbs run dry when the engine was last run. It is probably condensation or fuel residue left in the bowl of the carbs. Slacken off the fuel drain screws-nuts and let any fluid run onto a clean rag. Then get some carb cleaner from Motor factors, spray in the venturi with the throttle in the full open position. leave for 5 minutes. re prime the fuel system using the bulb.Try and run the engine up in a tank at the normal running depth. That should hopefully sort out the problem.

Cheers
Steve
 

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I
did the full service!
Today 14:41
Did you replace the spark plugs????

If you did , check that you hav'nt by accident cracked one, its dead easy to do without realising

IMHO

Cheers Ian
 

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Discussion Starter · #8 ·
Ok I will have a look at the plugs - I did replace them with new ones but I will check the spacing and look for cracks. Also will drain the carbs and see what crap comes out.

Ryan
 

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Hi Ryan,

Did you gap the plugs?
Does it have an inline fuel filter?
Different grade plugs can cause a lower tickover too.


Terry
 

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At the bottom of each carb is a slotted brass 10mm nut. Undo the bottom one a full turn and pump the fuel bulb. Look at the fuel that comes out of the nut, is it clean stuff, is there water in it. Pump the bulb until it runs clean. Close the nut up and nip it tight.

Repeat on the next carb up in the stack up to the top one. Try it again on the muffs. I would think this will clear the missfire. I am not a big fan of running a carb dry, it leaves a lot of air and a drop of fuel, that fuel evaporates relatively quickly and leaves a gum behind which can block up the carb. If you leave the carb full there is far more fuel in there and much less air so it will take a lot longer to dry out and leave the muck behind. With you now having run the engine the fuel in the carbs will be disolving the gum in there and the missfires can be bits of crud blocking the jets momentarly. Flushing out the carbs as I have described should clean them out if there is crud in there and stop it blocking the jets. If you can collect the fuel that comes out of the carbs you can ofter see pinkish coloured bits in it, this is the muck you need to get rid of.
 

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Discussion Starter · #11 ·
Drained the carbs as suggested and she is running sweet as a nut. There wasnt any water or pink stuff but there was a few bits of crud!!

So in future should I leave the carbs full of fuel over the winter?

I suppose starting her every so often will help with issues like this.

Thanks fellas,

Ryan
 

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Drained the carbs as suggested and she is running sweet as a nut. There wasnt any water or pink stuff but there was a few bits of crud!!

So in future should I leave the carbs full of fuel over the winter?

I suppose starting her every so often will help with issues like this.

Thanks fellas,

Ryan
I have got into the habit of running both main motor and aux on muffs for 5 mins every week. I trickle charge the batteries overnight every 2 weeks too.
 
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