[robuchanan]

2002 Carburetted 4 cycle 60hp. OT439784 (AUS).At about 600 hours running time, warning buzzer sounded. Reduced to low revs, 10 minute run to dock.Water OK. Oil little bit down, topped up.Normal running for about 4-5 hours. No more buzzer.But starts to sound like clattery sewing machine.Then sudden loss of power, under load. No buzzer.Revs out neutral OK. Low power and backfires 4000+ rpm. Limp home unhappily at 1500rpm.Carbys OK.Spark OK.Timing light says 5 and 15 and 28 btdc = OK.Compression 1&2 OK. 3&4= zilch.Remove Tappet (?poppers?) cover. Bottom 3 Rocker shaft to Head hold down brackets fractured and Rocker shaft bent.Purchased complete Head with valves etc, 2nd hand.Assured by wrecker, will bolt straight on OK.New head gasket, align timing marks, check valve clearances, all as per Merc workshop manual.Starts ok then dies. Jiggle carby throttle, will go, but not happy. Timing light says 10 and 20 btdc.?????????Pull flywheel, check timing marks, (several times by different people) appear to be lined up as per book. Valve clearances ditto.Oil and water sensors disconnected. No change.Could be ECM, but was ok before head replaced.Drive gear key OK. Driven gear dowel OK. Belt little bit slack but within limits.Live in small community with several experienced small outboard mechanics, but all are stumped.

[MercFan]

Sorry I don't know your engine at all. But for what it's worth. Is your ignition timing/trigger perhaps driven by the cam gear or cam belt?That's all I can think of that would change your timing when replacing a head on a four stroke. If it's a push rod engine the valve cam shaft sits deep in the engine and the timing can be driven from it aswell.Or if it has a over-head camshaft the timing could be driven from the crank via a cam chain or belt?

[robuchanan]

Thanks for the prompt reply.The timing is set with a timing mark on the external drive gear attached to;1.crankshaft under the flywheel.2.camshaft on top of the Head.Connected by a toothed rubber drive belt. When their marks are correctly lined up the timing should be correct, and No 1 cylinder valves are fully closed enabling the valve clearance to be set. Done all of that several times and checked by others.A sensor adjacent to the flywheel sends an appropriate signal to the ECM (electronic control module or Computer, Black box) mounted on the front of the Powerhead.This signal informs the ECM of the position of the flywheel at any given time and controls the timing advance/retard.The ECM also takes in information from the oil and water sensors and can reduce the engine speed to less than 2000rpm. I believe it does this limiting by retarding the spark.IÂ’m told by another 4 stroke mariner owner that disconnecting the oil and water sensors disables the limiting function, and IÂ’ve tried that to no avail.I am working from a Mercury manual published 2001, and they do say they will release updated bulletins which are not available to me.I feel that IÂ’m doing something wrong that will probably be obvious once itÂ’s pointed out by someone who has been here before me.Having already spent $2000.00+ so far my only alternative is to pack it up in a box, put it on a barge and send it 600 km to whence it came from, which I would rather not do, since it would mean my wife continuing a 3 times a week 38 km commute in my 4.3 mt Savage Gannet. And she feels much safer in the 5.9 mt UB Southwind. Luckily the Cyclone season is almost over and we have a few weeks (fingers crossed) of Doldrums before the SE Trades start to blow.

[WillyBWright]

Fuel problem. When it starves for fuel, the mechanical fuel pump sounds like it's going to hammer itself apart. You're sucking air or there's a clog. I've repaired a few tanks where the pick-up tube cracked near the top, one broke off entirely. That may be a good place to look.

[LubeDude]

Not to add insult, I honestly hope you get it fixed!But people wonder why we like out two strokes!

[robuchanan]

Thanks for the replies.On my way down to check fuel pump and filter now.This is my 2nd 4 stroke the first being a 1998 50hp Yamaha. Before that the dealer sold me the rig with a 1995 40hp 3cyl Yamaha 2 stroke. Which went fairly good till it was borrowed, and they put a drum of raw fuel thru it!!!!!!The only thing that has impressed me about the 4 strokes, apart from their lack of power, is the fact that I am no longer pouring 20 litres of oil into the water every six months.When this problem is resolved, IÂ’m thinking seriously of an Evinrude 60 Etec.

[robuchanan]

Happy Easter to all.Fuel pump seems to be moving fuel ok. primer bulb will be replaced, as one way valve is u/s.Decided time to get 50 yamaha out of storage. While transfering from dolly to workshop lift with aid of wife, she fell back lifting engine enough to fall back on my left big toe chopping off the end of nail and toe with the sharp end of the skeg. I know, I know, where were the steel cap boots? Still in the cupboard where they've been for the last ten years. I'll never ****ing learn. Did same with the right toe 20 years ago loading 44gal drums onto back of truck, thought i was doing so well rolling them on their edges till the last one rolled straight over the toe ********!So the saga continues.I'm out of it on rum and codeine till tomorrow.

[AMD Rules]

-OUCH-Just reading that made me wince in pain.Sorry to hear about your toe.