Out Board engine problem.....HELP !!

Morning,

Im looking for a bit of help with regards to a 15hp 2stroke Mercury outboard. Year 1999/2000.
The engine was serviced before we bought it.

Engine starts no problem and will idle ok, once in gear the engine runs good at 50% trottle (no cutting out or missing).

Had the engine going for a couple of hours at 50% throttle no problems.
If you go lower than this the engine cuts out.
If you go higher than this it just misses constantly.

The plugs are new and are the correct serial number for the engine.
The engine is not overheating and is passing water throught it fine.
I cleaned out the petrol tank and put in new mix of petrol and 2stroke oil (50:1).

The problem is still occuring,

Can anyone shed some light on this?

P.S. Im not too clued up on marine engines !

Cheers

Check the gap on the plugs Danny, also check your leads are in good order and are fitting correctly.

Might not have any bearing but you might just try turning up your idle speed a small bit too and see if it runs any better.

I am no expert but from what you describe it sounds like you have a dirty carburetteur problem. When run at 50% the suction on the fuel is good. When it goes lower it splutters because the fuel/air mix is wrong. Like Pete says this could be miss timing on the plugs because the gaps are wrong or it could be the fuel/air mix. Most common source is dirt from dirty petrol or crystalised fuel. Try removing carbureteurs and blowing through them. I might still be wrong but its a good place to start :?

Hi Danny,

I'd also be looking at the carbs.. Fairly handy job as well. Just be very careful removing them aas they all have gaskets and if cracked you will need to replace them.

Finiky problems like that can be very difficult to sort. Keep us informed.

One thing I noticed. I think you should be running a 100:1 mix on that engine. I don't think that is your problem though.

Kev

Hey Danny,

I think it is your carb.....can be reset with a screw driver...do it as the engine is running and you will hear the engine adjust. Hand book should let you know what the setting is. Sounds like the fuel mix is fine. A good thing to do is clean the plugs completely...not sure if plugs for that engine have gaps.....run the engine and look at the plugs again. See what colour they are ...if they are wet etc. That will let youi know if you r mix is too rich etc....if yoiur carbs are set right?

Thanks for the replys lads.

Might not have any bearing but you might just try turning up your idle speed a small bit too and see if it runs any better.

I tried that with no effect.


Im going to have a go at it again this evening.
Il check the Gap on the plugs. I bought 2 new plugs to try out too.

If that fails il try and have a go at the carbs.

Il keep ye posted.

Danny you should not have to adjust the carb. What Hush is referring to is your air screw. The air screw adjusts the amount of air mixing with the fuel. This should be set for your carb as is. Adjusting this means the air/petrol mix is wrong. If it is wrong there is a reason it is wrong and this does not solve that problem. The tube on a carb is very small and only a speck of dirt can cause problems. if this is the source of your problem you need to clean it or it will only get worse over time. My very first engine was an old Chrysler 50hp and had this exact same problem among others :roll: But i used to mess around with the air screw to get it to start and run etc. A dirty carb was the source of the problem.

Update,

Meself and Carpets had a go at the engine this evening:
What we done was:
Change the plugs (new plugs had a smaller gap between the electrode)even though they are the same make and serial number. We didnt have a calipers to measure the gap.
Took out the Carb and cleaned it with carb clearner (it didnt appear to be dirty on the inside) including throttle plate and linkages.
Played around with the adjustment screw on the carb while running(no effect).
Sprayed all electriacal points with contact cleaner.

Unfortunately were still having the same problems.
I think its time we dropped it in to a professional to have a look at it!

Also I noticed the engine has no form of air filter (like cotton/paper gauze), you can see straight into the throttle plate when you take the plastic cover off the engine.

I presume there should be some form of filter here !

Hey Danny,

Have a look IN the lower unit. Check for oil or ooze like substance at the bottom of the engine block..... I hate to say it, but I'm thinking small crack in the head gasket, especially if she is loosing power & spluttering at high revs.

Hopefully not...... :cry:

Kev

Hi Danny,
I had an identical prob, with a 2/s 70hp. Symptoms were very same - constant missing on full throttle and calfing it on idle.
Turns out TINY bit of water in the fuel had got through the carbs and jammed the jets. Just wondering, did you blow out the jets?

Hi Danny,
I had an identical prob, with a 2/s 70hp. Symptoms were very same - constant missing on full throttle and calfing it on idle.
Turns out TINY bit of water in the fuel had got through the carbs and jammed the jets. Just wondering, did you blow out the jets?

No , but im gonna blow them out when I get home :D !

Failing that il check for water leaking into the cumbustion chamber as per MACs advice.
Cheers.

Good stuff Danny, let us know how you get on. If you HG is cracked it will be an ooze like substance. Not water coning from the head. It normally spills it's way down the inside of the lower unit.

Kev

Update,


The Engine was eventually handed to a Mercury specialist in wexford.

The engine was compression tested and both cylinders are way down on their numbers, basically the cylinders are buggered.
We could go down a re bore and oversize piston route, but it was recommended that we get a new engine for it to be on the safe side:cry:.



I wonder would Santa be kind enough to bring me a Yamaha 4stroke this year ?

Sh!te..... Pity.

Hopefully Santa will look after you. Cheers for letting us know.

Kev

I wonder would Santa be kind enough to bring me a Yamaha 4stroke this year ?

NO.
He's bringing it to ME instead.