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Old 23 June 2013, 16:23   #1
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Tohatsu running rough

Was out earlier today at Cruden Bay, and the engine (Tohatsu M60C) sounded like it was running on 2 cylinders. Carried on to our fishing spot a couple of miles out. I pulled the plugs. The top one was wet and oiled-up, the middle and bottom one were dry. There was also a tell-tale petrol film in the water - so I'm assuming its running rich and not igniting properly?

I cleaned the spark plugs. Still didn't sort it, so I renewed the top spark plug with a brand new one, and then fitted older sparks I had on board for the other two. Engine ran fine after that, but I get the feeling its still idling slow. On the tachometer it looks like 850rpm or so?

I service the engine myself, stripped the carbs a few weeks ago (no adjustment to idle screws), replaced impeller, gear oil, new thermostat and fuel pump gasket kit. Sparks were new at the start of the year. I also renewed the water/fuel separator filter in the console and fuel bowl on side of engine.

Heading back, after we idled a little near the Bullers of Buchan it felt bogged down again. Rather than pull the plugs we carried on, but full speed was down as before. The fuel primer seems okay, and goes hard when priming. Tank was vented too. Tried switching tanks - no difference.

Pulled the plugs at home, dried them off and it idled fine when on muffs. Fuel was new this weekend.

A few weeks ago the buzzer sounded. I assumed it was a possible low oil warning. It's an autolube, so rather than risking a seized engine, I added some 2-stroke oil to the fuel tank. Think it was possibly a overheat warning, as it was idling before the buzzer sounded (retrieving anchor). I replaced the thermostat with a genuine Tohatsu part and renewed the gasket. That fuel (with extra oil) will have already gone through the system, and there was no ill effects. Tell-tale is strong, and impeller was renewed earlier in year, so no concerns here.

I can strip the carbs, but think they need balanced? Any suggestions greatly appreciated.
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Old 24 June 2013, 15:00   #2
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Spartacus,

It's a waist of time and effort guessing by fingering parts to find the culprit. That symptom works mostly on engines which have been long time grounded without running fuel dry on carb bowl untill engine dies of fuel starvation, specially on 2 stroker engines. Fuel evaporates leaving 2 stroke oil residues that gums internal carb parts producing miss behaving performances when giving jnuice to engine.

You seem to be experimenting ignition coil internal issues on the one that's producing wet tip excess. Don't know how old is the engine, electric parts are not eternal, will fail with use and time. Buy a new small ignition coil and test...

If striping carbs, but don't play with fuel/air screws unless you have a multi wacuum tester to adjust all 3 carbs at same time, or a philarmonic ear to adjust carbs by ear..

Usually measure with a vernier tool the height of the upper screw tip with respect to base when engine is new & out of the box, That way will be adjusted as factory delivered in the event wanting to pull screw off to clean all carb related parts.

Happy Boating
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Old 26 June 2013, 02:28   #3
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Thanks Loco.

Engine is 2006 M60C 3 cylinder.

I agree about not messing with the fuel/air screws. It's been running fine, but the top cylinder plug is usually fouled. That one at least could be adjusted so it runs a little leaner - don't you think? I checked the engine before a couple of months ago (had sticking butterfly valve) and there is spark on all three plugs. Sure the HT leads could be possible culprit? The fuel air screw from lightly seated turned out by 1 + 1/2 turns? I'll establish its current position first.

In addition, I can up the rpm at little, as it feels slow at tick-over. I'll check the manual for idle speed (operating manual, not workshop manual) and adjust. As discussed - it controls all three carbs.
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Old 26 June 2013, 06:22   #4
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If you added oil to the fuel and there was still some dregs in the tank, it may be fitted with a rev limiter type arrnangement like my old Suz - when it hit "low" it rev limited, when it hit "empty it essentially pulled the deadman on you to prevent it siezing.


Other thought - (I had this at Easdale this year) - if you had the plufgs out are you absolutely sure al lthe HT leads are back on? I thought I had properly replaced mine, but the top wasn't quite pushed home and needed an extra heavy shove to get it to "click" into place.... I had had a concern they may be loose so had pulled them off to squeeze the terminal in a little on each cap. Bottom two had clicked back on - top (probably due to the angle / height etc as I stood behind the trailer) had gone on "solidly" but not quite clicked in properly electrically......
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Old 26 June 2013, 10:57   #5
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Spartacus,

It's normal to find one out of 3, 1 out of 2 more fouled plugs, think it's always the upper one which fouls more than lower ones. So all small Ignition Coils are working ok ? Sometime ago had a bit power loss on a 40C Tohatsu, the metal contact inside cap plug was found bit corroded, cleaned it, bettered performance just a bit, unscrewed the cap and found cable wire end being dark in color, cut 3 mm in lenght, wire color was completely shinny, screwed back cap, turn engine on, made all the difference.

Sometimes electrical hidden issues will give you trouble, specially the ones which are difficult to troubleshoot as in this case, same as when having issues with electrical components overheating when under load. Adjust main rpm screw, which controls all 3 carbs to at least 950/1000 rpm, 750 is bit low, could stall engine when engaging.

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Old 26 June 2013, 11:25   #6
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could it be the plug cap itself rather than the lead ,
on some of the rubber caps
ive had a couple where the metal spike inside hasent gone right through into the conductive wire part of the lead or its corroded/burned away or just come off inside even by just pulling plug cap off the plug thats caused a bad spark .
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Old 26 June 2013, 13:02   #7
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Quote:
Originally Posted by 9D280 View Post
If you added oil to the fuel and there was still some dregs in the tank, it may be fitted with a rev limiter type arrangement like my old Suz - when it hit "low" it rev limited, when it hit "empty it essentially pulled the deadman on you to prevent it siezing.
I confused what was probably a temperature sensor buzzer fault for low oil. It's an Autolube, so I added a glug of 2-stroke straight to the 25 litre tank. That was a couple of trips ago, so there has been fresh fuel through that fuel tank without oil. I topped up the Autolube tank on the engine - but never let it go anywhere near empty. I also replaced the water-pump impeller (start of the season) and thermostat (before the last trip out). I don't know if the M60C has a rev-limiter function or not?

Quote:
Other thought - (I had this at Easdale this year) - if you had the plugs out are you absolutely sure all the HT leads are back on? I thought I had properly replaced mine, but the top wasn't quite pushed home and needed an extra heavy shove to get it to "click" into place.... I had had a concern they may be loose so had pulled them off to squeeze the terminal in a little on each cap. Bottom two had clicked back on - top (probably due to the angle / height etc as I stood behind the trailer) had gone on "solidly" but not quite clicked in properly electrically......
Yes, definitely on, and tell-tale 'click' as the HT rubber insert connects with the spark-plug. However I will take a closer look at the coil/HT leads. They look fine, but I may need to replace that top one if problem persists.
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Old 26 June 2013, 13:08   #8
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Quote:
Originally Posted by Locozodiac View Post
Sometimes electrical hidden issues will give you trouble, specially the ones which are difficult to troubleshoot as in this case, same as when having issues with electrical components overheating when under load. Adjust main rpm screw, which controls all 3 carbs to at least 950/1000 rpm, 750 is bit low, could stall engine when engaging.
I will check out plugs. Haven't tested them yet.

I'll also up the rpm to 950 rpm (but leave fuel air mixture screw setting) and see how it feels. When I was running it on muffs after our last trip at the weekend, it was purring like a kitten at idle. Tell-tale was like a Clydesdale horse having a pee!
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Old 26 June 2013, 16:29   #9
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One thing is running engine on muffs, other on water. If adjusting rpm on muffs, surely engine will die once on water, need more rpm to compensate exhaust being near blocked under water rather than out of water when with muffs. It's better to adjust rpm once on water and well warmed engine.

When rpm is adjusted on water, propably will achieve slight more rpm readings when on testing/flushing on muffs, but that's ok. The times that have lowered rpm on muffs, engine has stalled once on water. 2 strokes horses are sometimes unpredictable running at low idle rpm.

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Old 27 June 2013, 04:39   #10
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+1 for loco's in water / on muffs.

As Mchappelow says, it doesn't take much wrong with an HT lead to kill a spark. Do you have a spark tester? Use it o mnthe lead and you might be surprised. Oprtion 2 is if you have or have friendly spark with as megger do an insulation test - your multimeter will say "insulated" but 1.5V DC might reckon it;s fine, but throw a couple of KV at high frequency at the leads and suddenly they donlt insulate so well.....

Same goes with the spark plugs - which is why they should be changed reasonably frequently.
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