Mariner 135 running rough !

paddlers · 15 August 2014, 19:53

My 90's Mariner 135 V6 is running rough. Put in 6 new plugs and run some Redex through the petrol. Tickover not too bad but pick-up and top end not quite there. Max revs appear to be @4500 rpm under load but revs easily to 5500 using just the fast idle lever.......
Starting a bit hit & miss sometimes needing choke but not guaranteed..

Any clues where to look next. I'm not keen to strip the carbs down as the river is tidal and I'll probably lose something.

camarine2009 · 15 August 2014, 20:41

Don't bother running any cleaners through with the fuel especially Redex as they don't work. The only way to clean carbs is to remove and strip them down. Not an easy task if the boat is on the water but can be done if your careful. I always diagnose running issues with a compression test in the first instance to make sure all cylinders are within 10% of each other. I then quick check the stator/pack output using a DVA meter and finally gap test the spark output. If you have a timing light you can quickly check the timing at cranking speed which will rule out a sheared woodruff key (very unlikely but have seen it) if all ok you gotta pull the carbs. Don't worry about stripping them just take your time and be methodical and refer to the manual if you need to. Good luck and I hope you resolve the issue.

paddlers · 15 August 2014, 21:22

Found a corner chunk of magnet @15mm each straight side lodged below the flywheel tonight....... Will that be the problem?

camarine2009 · 15 August 2014, 21:35

Yes could well be If the flywheel magnets have come loose. This will without a doubt cause a running issue. You will need the correct puller to remove the flywheel don't think you can remove the nut and hammer it loose as so many people try to do. You can re glue the magnets back in as a cheap fix but ideally a replacement flywheel is the answer. At least you may have a lead to the problem.

paddlers · 15 August 2014, 21:43

I was REALLY hoping that you weren't going to say that..

Thanks for your help with it. I'm still able to get out fishing & pull a skier out so the work hopefully will wait until the holiday's over next week. The rest of the magnet seems to be firmly stuck on so a bit of a mystery why a corner should break off !

camarine2009 · 15 August 2014, 21:50

They usually fracture just due to old age nothing else apart from the flywheel being whacked with a hammer. The Merc/Mariner v6 is good engine and looked after seem to run for ever. Good luck and hope it doesn't end up being too costly.