Can anyone diagnose my donk problem?

[Adamy]

I have a "strange" problem with my outboard and have no idea what it could be... maybe someone here has a clue - or even a suggested place to start looking??

The motor is a 80hp merc blueband and has been going great. So I'll describe the symptoms and see what you think...

I first noticed that it felt like I was pushing the boat uphill, it took more and more revs to get it to the speed I wanted - usually it will cruise fairly economically at 4200-4500 revs and go about 21-23mph on a fairly flat sea a little less in slightly rougher conditions which we experienced yesterday.

At 5000+ revs in a following sea - probably half metre of acceptable swell and chop - no whitecaps - I was going between 13-15 mph and slewing and digging in between the sets - despite having the nose lifted a bit by trimming the motor out. I really felt like we had a belly full of water and having a hard time pushing it uphill.

In fact it felt so much like we were full of water that I was concerned we had cracked the hull somehow and were taking water - but when we pulled it out and drained it - there was less than a cup in there.

Anyone have any idea as to what this could be?? There was no cavitation and no looseness or slap in the prop. Could it be a gearbox problem???

Thanks in advance!!

Adam

[blaze]

give ya boat a rock on the trailer just to double check the water thing, may have a semi sealed comparment under the floor that won't let the water drain. Just an early thought. You seem to be descibing extra load that is constantly moving.
cheers
blaze

[FNQCairns]

Prop hub bush, sometimes they go slowly yours sounds as if it is slipping when hot. Might not do it when cold but after some exhaust heats it up it starts to slip. pretty soon you will be going nowhere -if I guessed right that is.

cheers fnqs

[Roughasguts]

Hmm interesting me like these.

So if the hull under floor compartment ain't full of water. tapp under the hull feel for a dead thud to see if there may be water trapped in the floor.
But if the boat floats on a even keel and level, well it might not be.

other thing is you motor, what speed does it idle at nice and low or over 1000 Rpm, does she cough and sneeze, and take full throttle easily.

Could be a number of things at this stage.
Change the plugs.
Drain the carbs.

But i'm thinking your reed valves may be stuffed, them the little fingers of metal like feeler gauges behind your carbs. But any way if she won't idle at normal revs then I would suspect the reed valve.

[jimbo59]

You might have dropped a cylinder or2?

[triman]

Yep, reed valves are the first culprit

[impulse492f]

I had the same thing happen in Botany Bay yesterday. If your motor/boat works ok in smooth conditions. I don't think its your boat or motor but simply the following sea's.

How big is your boat? mines 16' and with a decent swell, wind chop and wave length the boat gets caught in the trough.

You can try different driving techniques to get ahead of the wave directly behind you and its best to ride the back of the wave in front, try not to power over it or let the one behind break as there is a change of broaching sideways which could cause problems.

[Spaniard_King]

FNQ is on the money... think about it..its doing 5000rpm.. so there aint an engine problem but more like a power transmiting problem... most likely a hub hs spun on the prop

Garry

[blaze]

when read the right way with increase revs and no speed it does point to prop.
cheers
blaze

[tigermullet]

After trying to think my way through the problem have come to the conclusion that FNQ, Spaniard and Blaze are probably right. With a punch mark either side of bush directly opposite each other - just a gentle tap should do it and then go for a run in the boat. You will soon see if they are out of alignment on inspection after the run.

[tigermullet]

Damn! forgot to add -- if out of alignment it means that prop is slipping and needs re bushing or replacement.

[finga]

I'll throw a spanner in the works fella's....
We've tried different props and one was my old one with a known good bush....sorry :(
I'm going to see Adam next week to have a gander at the motor setup ie motor heights etc and take some pictures (and so he can show me how to use these bloody mongrel plastics to get a fish maybe).
More info to be added to the mystery I'd say.
But please keep the theories coming. More the merrier. :)

[FNQCairns]

Well if 5000rpm can be believed, you have added weight, how did you fella's decide the sealed chambers are not full? If it has them. but the prop hub is still the most believable option, water in the hull is a wildcard without the ability to view it.

If 5000rpm cannot be believed check for tacho problem coinciding with an ignition problem.

One very important diagnostic tool is whether the engine still has the same WOT before as after the problem.

cheers fnq

cheers fnq

[bungie]

Just checking, umm, you did take the boat off the trailer ?? :)

[bungie]

slewing and digging in between the sets - despite having the nose lifted a bit by trimming the motor out.

Sounds like weight moving around in the boat, hence the hull holding water ?

[Roughasguts]

So does the motor feel like she's lacking torque, eg not holding rev's and not pushing out of the trough, but rev's freely at othertimes.

If so, well it's looking more likely the reeds.
Sorry those are exspensive on Mercs. But it's the reed valves them little fingers that gasses suck through the carbs, then close shut on compression so as not to lose any charge, eg: escape back through the carb before the power stroke. So if they have lost there tension they will no longer work and close off when required.

It is almost like having your intake valve on your four stroke not sealing.
The rev's will be there but not the power.

Just wondering if you can turn the reed valves over, that ought to put back the tension where it belongs, But it wouldn't work for long as they probably have metal fatigue, as these things flutter open and closed with every stroke, they get a work out.

Think reed valves, are a Yamaha Original invention.
Suzuki the oil injection.
Wish Kawasaki, would get in to outboards.

[tigermullet]

If slipping prop theory is blown out of the water then more information is needed. This is an interesting and challenging problem.

What sort of boat? It's beginning to sound as if it has a gutful of water.

[Adamy]

Geez... thanks for the input guys!!!! all this sounds interesting and quite technical - think its a bit above my head. I think the tacho is right because I can hear the motor and at 5000 it still sounds like 5000 - there did seem to be a lower hum though that I havent really heard before like a big power boat makes - in fact I kept looking back to see if a big cruiser was following us. does that help in the diagnosis??

re the prop - it isnt slipping at all - I'm sure about that - theres no cavitation noise my mate who was with me has spent his life at sea and on the water as a fisheries inspector - so he knows a thing or two but couldnt tell what this was but said there was no cavitation or slippage. The prop is a 17 pitch - I dont know about the bushes tho - if they slip wouldnt this cause caviation?? I had another prop one time where the bushes slipped and there was massive cavitation - this was totally different.

We did have 2 eskies - probably with an extra 70kg in them with about 3 or 4 buckets of water - but we had on a similar load the day before and not as much problem or actually no hint of the problem - I like the sound of the reed thingy idea - but have no idea what it means or how to go about it.

Roughasguts - yeh I think lacking torque would be a good way to describe it - increasing revs but not actually going anywhere. Hey scotty - have any idea what this reed thingy is all about?? can we look at that when you come over? and how can you tell just by looking?? Feeling a bit like a newby here.

oh to answer a question or two... its a 16.5 ft (5metre) cuddy cab in glass... I'll go tap the bottom to see if there are water pockets now...

Thanks for all your help and suggestions - very much appreciated!!!

Adam

[blaze]

if the engine is doing 5000 revs, then the prop has to do the correct revs in relation to the gearbox ratio. If the prop is not doing the correct revs then there has got to be a break in traansmission drive somehwhere, the most obvisous place is the bush in the prop. I believe if it was something like reed valves you would not achieve 5000 revs in the water as the torque would be lost, I think the only place 5000 revs could be achieved is on the muffs. If the full drive line is ok (prop bush etc) and you are indeed achieving 5000 revs then your theretical speed shoud not have altered. If you indeed have extra weight (such as overload or water in your hull), then the revs will not peak to the 5000 revs you mention because it will have the same effect as a cas going up hill and lugging (car up hill slows down and go down hill, increase speed and revs)
cheers
blaze

[jimbo59]

Has the boat got antifoul.

[Roughasguts]

Adam, this noise you talk about does it sound like the motor has dropped in pitch, Eg: a bit duller ? lower octive, Sorry not a sound man, Then pop out of it so to speak.

Could be a coil pack dropping in and out, and the noise is from induction, with out the gasses going bang.
Only talking on lung not all four.

[Adamy]

Adam, this noise you talk about does it sound like the motor has dropped in pitch, Eg: a bit duller ? lower octive, Sorry not a sound man, Then pop out of it so to speak.

Could be a coil pack dropping in and out, and the noise is from induction, with out the gasses going bang.
Only talking on lung not all four.

Now you got me roughas... I'd say yes - but the "normal" noise is still there - this was like an extra noise. It was constant at the higher revs.

Jimbo - sorry mate - I dont think shes got antifoul - I dont even know what it looks like

Blaze: I have a couple of 19 inch props here - we'll give those a go and see what happens - that should sort out whether its the bushes on the current 17??

At any rate - seems that finga is coming over on Wednesday - we'll have a look at everything everyone has mentioned - or may yet mention - take some notes and let you know what happens - his eye and ear may (probably definitely is) better than mine - so may be able to pin point it further.

So if there are any other suggestions - or places we should look - feel free to add to the discussion - we'll find it eventually!!

thanks all!!

Adam

[Angla]

Just a different angle

Were you in unfamiliar waters that were subject to strong currents or just in conditions you were familiar with?

Has the gearbox oil ever been checked?

Chris

[Roughasguts]

Adam, whatever it is your going to have to take the boat out again you won't be able to replicate it on the muffs.

But before you take her out drain the carby float bowls, see if there is any water or gunk in there, 5 min Job.

Drain the fuel water filter seperator, and clean the engine petrol filter, look for gunk.
If the engine filter is dirty there maybe a chance one of the carby jets is partially blocked.

And clean or replace the spark plugs, carby clean, is great for cleaning spark plugs.

But if it checks out fine, then all it was, was your over loaded esky's weighing the arse end of your boat down. So next time you fill them with beer and ice move them further forward, where you can reach them better.
Oh yeah the boat will plane better as well.

A 16 footer don't like being arse heavy.

[tigermullet]

If it is a stuffed prop bush you will not get cavitation.. For cavitation to occur air must be introduced to the propeller blade/water interface by having the motor at the incorrect height, something causing turbulence etc. Cavitation can be exacerbated by having the prop pitch too low but low pitch is not the primary cause of cavitation.

Therefore if the bush is stuffed and the propeller not rotating properly i.e., slipping it will be 'travelling' much slower than normal and cannot, of itself, cause cavitation. Bear in mind that the 'cavitation plate' is really mis- named. We would be better off remembering that it is an 'anti ventilation plate'.

This fascinating problem continues! It will be great to hear the solution.

[Roughasguts]

Adam I'm starting to think you haven't got a problem, only badly loaded with to much rearward weight.

My crystal ball is a bit foggy tonight.

Thinking The noise you hear is the motor almost lugging trying to get it's arse out the water and working bloody hard.

So a motor working hard is going to get high cylinder head temps, so how is the tell tail and water pump?, Plenty of oil getting in to the motor ?
Working okay cause if not.

Your going to get your wallet burnt.

Also wouldn't hurt if you touch test the cylinder head at some stage while the motor has been running, or idling after a run.
(Watch your fingers on whirly things if it ain't got covers)

Use a differant finger every time, just hold your finger on the cylinder head and count how many seconds until it's uncomfortable if up to 7 seconds it's okay. But if your skin sticks to it like a barbecue plate, then apart from going to the emergency burns unit, Your motor also has a cooling problem.

But don't worry your morning cup of coffe is hotter to touch than your out board motor.

But if the motor is getting bloody hot, and you have plenty of lube, then were looking at some form of seizure between piston and bore, slowing things down, and changing the engine note somewhat.

[gonefeedin]

hi
found this site it as been very good for me i have found some probs and they sorted them out http://forums.iboats.com/bbBoard.cgi

kev

[Spaniard_King]

Its possible that the tacho is not reading correctly and infact you are not achieving 5000 rpm

Garry

[Adamy]

This is great - more grist for the mill - I may even learn something at the end of the day!!

Regarding overloading - all the weight from the two eskies was in the middle of the boat - under out feet - although some of it did shift to the left while we were slewing about - so maybe that had something to do with it?? I'm about 65kgs wring wet and my son about 30kgs - my mate about 70 - 75kg was on the left side while one esky with about 30kg was in the middle and the other esky (80cm long) with maybe 40-50kg wasin the middle section - but half way toward the left hand side of the boat.

Could I have just had a weight issue?

At any rate - I think a sea test with an empty boat will tell us if that was the problem - if the problem still exists - then looks like we'll be working through the suggestions here one at a time till we find the solution.

Tacho problem... IF its a tacho problem - how do I tell? at WOT I achieve about 6500 - so if I achieve that then there shouldnt be a tacho problem correct??

What I really should do is throw a keg party and invite you bunch of brains over and we can discuss it (and fix the damn thing) over an ale or 7!!!:P How many contributors have we got from Brissie?? Blaze... Rough as... can you travel?;D

Thanks All!!

Adam

[Roughasguts]

Adam I think you where heavy add the fuel tank, battery and motor, following seas and I think that combo is the problem.

[gone_fishing]

interesting prob you got yourself
definatly sounds like a prop bush
but if youve tried different props already:-/
its going to be a bit of trail and error:(
exsess wieght as suggusted
motor postion has it moved??
bolts come loose transom damaged??
motor trim leaking down ??thinking you trimed the motor up to have it lower the nose again
all the best keep us posted;D

[finga]

There's going to be an update by Adam soon fellas.
Lots more information to try and get the problem sorted :)

[Mark-P]

Just a thought Adam . If the leg was letting water into the gear box, the combo of the two fluids mixing might be causing the prob . It would account for the excess noises & loss of speed ?????? Just a guess really !!

Mark

[gone_fishing]

hi adaamy how did you go ????
any answers yet?