Mercury 60 2 stroke

xr770a · 11 November 2019, 15:46

Hi all,

My Mercury 60 stroke (3 cyl circa 1994) starts fine, but when I give WOT it does not rev up (only 2k), I shift my weight about the boat starts to come on the the plane (revs start to rise slowly), then the revs rapidly rise like no tomorrow a real "turbo rush " of power up to 4.8K..its a nothing nothing nothing bang ! It always does this now from low revs, hot or cold. I have fitted new fuel filter and drained the carbs, new battery, top tesco 99 fuel.This appears to have happened in between outings.. sounds like something sticking ??

Help please

neil.mccrirrick · 11 November 2019, 17:02

It sounds like there is a lot of weight in the boat that is then more evenly balanced when you are on the plane. I’d check for water in the hull as a start before anything else

Pikey Dave · 11 November 2019, 19:35

Quote:

Originally Posted by xr770a

Hi all,

My Mercury 60 stroke (3 cyl circa 1994) starts fine, but when I give WOT it does not rev up (only 2k), I shift my weight about the boat starts to come on the the plane (revs start to rise slowly), then the revs rapidly rise like no tomorrow a real "turbo rush " of power up to 4.8K..its a nothing nothing nothing bang ! It always does this now from low revs, hot or cold. I have fitted new fuel filter and drained the carbs, new battery, top tesco 99 fuel.This appears to have happened in between outings.. sounds like something sticking ??

Help please

Is it topping out at 4800 rpm or does it go higher? If so what’s your WOT rpm?

jeffstevens763@g · 11 November 2019, 20:58

Yep I'd go water if nothing's changed are you propped correctly 4800 sounds low at WOT maybe water stopping you achieving a smooth displacement to planing speed with too high a pitched prop. Not familiar with mercs re RPM optimum window but moving weight is helping it to overcome the extra weight.

xr770a · 12 November 2019, 08:07

Hi All

Weight or the prop is not an issue, as it was perfect 2 weeks before this and always has been, this is a new problem, a 60 on a 4m rib should get it up quick, I have towed 2 biscuits before easily, now no chance, something has changed in the motor. There is no water in the hull. Its as if something is sticking in the motor which suddenly frees is self when the revs start to rise, you could not get it to go suddenly to full power like that yourself.

Fenlander · 12 November 2019, 12:59

I don't know this outboard so just generic advice...

I see PD above asks if your revs usually top out at 4800 WOT. Because if so it sounds as if you are a bit over propped and that could mean the slightest problem with the OB being below par and immediately getting on the plane is an issue and it does sound, as folks are saying above, like a classic getting over the hump situation.

Have you checked the throttle lever is still getting all the carbs fully open? Is there any way the cable system could have intermittent lost motion so you weren't getting fully open at the carbs all the time?

Some very basic checks after that... fit new plugs regardless of how the old ones look (are there any clues from look/differences of old ones?)... check ign system all looks clean (start in dark if you can and look for tracking)… strip and clean carbs... test cyl compressions.

davej · 12 November 2019, 16:44

4800 rpm is certainly low for wot as I have one of these on my tornado 5 mtr. I think my diving prop is a 13 inch pitch. This seems perfect as it goes well with 4 divers on board and will easily rev to its limit of 5500.

However, go to a 14 prop and is rubbish with some weight in and wouldn’t get on the plane with any divers onboard.

Sounds like you are overpropped

jeffstevens763@g · 12 November 2019, 18:29

Throttle cable corroded and sticking?
Does it run rough at all through the Rev range and will it stay at 4800 for long

neil.mccrirrick · 12 November 2019, 18:50

If the revs increase as you come into the plane then it’s failing under load. That would indicate too much weight, or bad compression, or poor spark. That could be an arcing HT lead, drag on the hull from something or worn piston rings. Something to think about anyway

phantom 19 · 13 November 2019, 06:07

Quote:

Originally Posted by jeffstevens763@g

Throttle cable corroded and sticking?
Does it run rough at all through the Rev range and will it stay at 4800 for long

More likely to be a problem with the advance / retard mechanism sticking

xr770a · 13 November 2019, 08:22

Hi all,

Thanks for all the help so far, I think Phantom 19 may have the answer, I spoke to a boat mechanic he said coils...nah ?. I have owned a 3 cylinder 2 stroke Kawasaki motorbike for years and know all about keeping it in fine working order.
Cannot see that, as it starts and runs at top end fine ( when there is the most demand for a quality spark), what ever it is affects all 3 cylinders, I cannot imagine all 3 carbs get blocked or all 3 coils to fail, the engine is as smooth as silk (for a 3cyl).
Brand new cables fitted last year (by dealer) giving full throttle (had intake off and checked that ) Plugs are perfect colour, perfect compression on all 3 cyls (within 3psi of each other) It will stay at 4800 all day smooth as.
No tracking, new plugs and a massive fat healthy spark. Carbs drained no water or sediment from them.
Time to soak all joints on motor with wd40 to clean them, then a good dose of ACF50 (amazing gear, used on my motorcycles for years, you all need to try it)
Will keep you all posted on outcome.

Ribtecer · 13 November 2019, 16:33

I think its a fuel problem myself. Whatever it is it's very annoying. Good luck finding it

xr770a · 21 November 2019, 11:40

Still a mystery, looking at advance retard mechanism...

xr770a · 02 December 2019, 14:18

On close inspection when the throttle is opened I notice the section going up to the advance / retard mechanism under the flywheel was not opening fully ( about 10 mm short of its stop) plenty of lube and manual intervention it now opens fully on its own.....cannot tell if it works until the next time im on the water