Mariner 15 2-stroke spitting fuel near carb.

Fenlander · 13 April 2015, 09:38

My Mariner 15hp 2-stroke is a 2004 and was new to me last autumn so I've not used it much yet or done any work on it.... just given a plug change and lubed pivots etc.

The other day on the first outing of the year it started and ran OK but wasn't perfect at idle.... dying once when still not fully warm and idling at the pontoon. Took about 10 pulls to restart and needed holding well above idle revs for 30sec to "clear" it before we were happy to go off.

Was OK for the rest of the day but didn't ask it to idle for any period in case it happened again.

When flushing the next day at home in the tank it seemed OK but I noticed at idle it was spitting very small quantities of fuel from around the fuel pump side of the carb in the place shown in the image below. The source seemed to be down the back of the fuel pump or from the carb near its flange to the engine.

Unfortunately even with a torch it was impossible to pin down the exact place this was coming from due to the clutter of the throttle/gearchange pivots etc.

Going to get the carb off soon hoping it's obvious what's happening but any ideas much appreciated.

Note: The fuel wasn't spitting from right at the end of the arrow in my image but from somewhere behind that point.

Nos4r2 · 13 April 2015, 10:10

Was it a regular spitting?

Fenlander · 13 April 2015, 10:20

Hard to be precise as it was so windy and the tiny "jets" of fuel were so small. They appeared to come from (in my image) between the back of the fuel pump and the black plastic throttle/gearchange parts... and below the white plastic throttle cam.

Thinking about it there may have been some relationship between the engine pulses as it idled and the timing of this spitting. What are you thinking... fuel pump?

I'd say it was less than a jet but more defined than a mist... if that makes sense.

Nos4r2 · 13 April 2015, 10:44

I'm thinking fuel pump/diapragm or fuel line. Probably the seal between the pump and the crankcase as 1st goto.

Fenlander · 13 April 2015, 13:03

I'll get the carb off soon... front springs to do on car first! Hopefully it will be obvious what's wrong as once the carb/pump assy is off I can't replicate the spitting.

Luckily I have a Mercury spares/service outlet only 10mls away so I can get any individual parts I need. Seems in the UK it isn't easy to find a complete carb/pump gasket/overhaul kit online... well apart from some place in Soham that has one on Ebay!!

Max... · 13 April 2015, 13:21

Can highly recommend Black Dog Marine for help with Mercury/Mariner and obscure parts needed - may be worth a call to describe symptoms...

Fenlander · 13 April 2015, 14:12

Good call Max.

Seems they have a carb/pump overhaul kit for mine plus some individual bits.

I'll get the carb off once I've done the car then phone them.

Fenlander · 15 April 2015, 12:32

Carb off now... this Youtube guide was a help... not that it's that complicated but the method of removing the plastic choke/primer wasn't immediately obvious until I watched the video.

https://www.youtube.com/watch?v=rpcrTt5WMUE

Problem obvious once the carb was off... this pipe split at the end that should connect to the brass boss on the carb flange.

So new pipe and that'll sort it.

Max... · 15 April 2015, 12:39

Nice easy one - makes a change!

Fenlander · 15 April 2015, 12:39

Just thinking... what does that pipe do... some sort of breather or pressure balancer?

It comes from the carb flange to a tee then off to bosses on the very upper and lower crankcase areas (see pics).

At the carb flange end when the carb is bolted on it effectively connects with that brass port thing with the two holes on the engine flange side (see pic).

When I turned the engine over by hand a small amount of fuel was spat out from the split hose.

Fenlander · 15 April 2015, 12:44

And the other thing... do I just replace the pipe and assume all will be fine or do the full carb overhaul while it's off... or at the very least just replace the pump diaphragm??

I can see from the screw heads the fuel pump has been off before so may have a relatively recent diaphragm prior to my purchase.

I did just pop the jet out of the bottom of the float bowl that drains it and there wasn't a hint of debris in the jet or fuel that came out.

Would be nice to think it was all done with new gaskets but sometimes once you touch a carb on an outboard... superstition and all that!

Fenlander · 20 April 2015, 11:14

Just an update on the solution...

When I took off all the "balancing" pipes (that's what the local Mercury dealer called them, for crankcase pressure balancing he said) I found the bottom one was split too near the crankcase end.

Mercury dealer couldn't help with the pipe but I went to the garden machinery place in town and their very on the ball parts guy soon found exactly the od/id I needed, £1.50 for 50cm. It was fuel pipe for an Oregon chainsaw. Image attached.

Cheap repair for that part of the job then.

He commented they are supplying loads of fuel hose as the modern unleaded affects rubber hose on older machinery.

Probably worth any owner of similar model Mercury/Mariner outboards replacing this hose during a yearly service rather than waiting for it to split.

Decided to do the carb clean and overhaul while it was off.. will do a separate thread for that.