Evinrude 70hp problem

[Historicalgasman]

Hi all, firstly I will apologise for my total lack of understanding, but this is my first rhib and outboard so I'm on a learning curve.
Right, my problem, ran the engine yesterday on Loch Fyne and at first it was running sweet, we did a run out and back opened it up to see what she would do, 25 knots and all was great, on our second run out we picked up a fishing line around the prop, jumped in and got it all off. After that we set off again and all was well after 10 mins of running we arrived close to a dive site I slowed down, we decided to go to the next site, when I opened the throttle all I got was 7 knots. I put her into neutral set off again and I got power, then it dropped again I found that by moving the throttle leaver you could feel the engine bite and then it was of at full revs.
Engine idles fine, selects gears fwd & rev, no miss fires just this loss of power.
I have the workshop manual but I'm looking for some info in simple terms for a simple newbie!
Thanks for any help.

[Landlockedpirate]

Its possible that you have spun the bush in the prop, this happens naturally over time but the line round the hub could have accelerated the damage.

You can send the prop off to Steel Developments to be rebushed.

[Historicalgasman]

Thanks, when I take the prop off, how can I tell if that is the case?

[Poly]

You want to put a mark/line across the radius of the prop so that the centre and outside are both covered (e.g. use indellible pen or tipex depending on colour of prop) then take boat for a spin to get the symptoms you describe - afterwards if the mark is no longer one continuous line it has been slipping.

There is a prop repair place in Clydebank which will save you postage if you are passing.

[Historicalgasman]

I work in Clydebank, I take it you mean I mark the nut in the centre and the rim of the prop and if the 2 don't line up off to Clydebank with the prop. Do you have the name of the company?

[Historicalgasman]

Reading the manual, it describes similar symptoms and says its the fuel pump, what do you guys think?

[Landlockedpirate]

Is the loss of power a loss in forward motion with revs still on the max or a loss of revs ?(i.e. you floor the accerator and the engine doesnt rev)

[Historicalgasman]

Originally Posted by Landlockedpirate

Is the loss of power a loss in forward motion with revs still on the max or a loss of revs ?(i.e. you floor the accerator and the engine doesnt rev)

I havent got the rev guage connected yet, but the engine wasnt at full revs even with the throttle fully forward, but it would then jump to life with a wiggle of the throttle and you could feel the engine bite, on the way back in it was surging itself going from 7 knots up to about 16 without moving the throttle.

By the way I'm from St Helens!

[Pikey Dave]

Originally Posted by Historicalgasman

By the way I'm from St Helens!

Ahh, that explains it

PS it doesn't sound like the prop is slipping, what model of Evinrude is it? Etec, FICHT (don't think they made a 70hp FICHT but I could be wrong)

[Historicalgasman]

Originally Posted by Pikey Dave

Ahh, that explains it

Steady now, at this Christian festival we don't want to ignite the Lancashire, Yarkshire battle.

[Historicalgasman]

Its an old one from 1984, theres no model name on it, but theres a pic of it in my album.

[Pikey Dave]

Originally Posted by Historicalgasman

Its an old one from 1984, theres no model name on it, but theres a pic of it in my album.

In that case it'll be a carbed engine. You need to be methodical or you'll just end up jumping from point to point. I'd start with the fuel system, check the tank vent if you're on portables. Tank pick up, is there any crud in the tank? Fuel line, is it cracked, leaking air at any joints? Primer bulb, does it go soft or collapse when the problem occurs, when you pump it, does it go & stay firm? If all that lot checks out, you're into the engine, fuel pump, carbs. If the fuel system is all ok, then start on the ignition system.

Enough there to be going on with. Sorry there isn't a magic answer, these things are mostly solved by time & swearing.

Welcome to boats

[Historicalgasman]

Originally Posted by Pikey Dave

In that case it'll be a carbed engine. You need to be methodical or you'll just end up jumping from point to point. I'd start with the fuel system, check the tank vent if you're on portables. Tank pick up, is there any crud in the tank? Fuel line, is it cracked, leaking air at any joints? Primer bulb, does it go soft or collapse when the problem occurs, when you pump it, does it go & stay firm? If all that lot checks out, you're into the engine, fuel pump, carbs. If the fuel system is all ok, then start on the ignition system.

Enough there to be going on with. Sorry there isn't a magic answer, these things are mostly solved by time & swearing.

Welcome to boats

Cheers, the fuel tank is brand new, although when I took the tank off yesterday it was leaking from the hose conection as it wasnt screwed into the tank fully, primer bulb did go soft but when I pumped it it stayed up, I took the air intake off to have a look at the carbs and they looked clean enough but I will get new gaskets strip off and clean etc,

I'm guessing there isnt much I can do to the fuel pump other than replace it, where is the best place to get parts?

Cheers for the advice!

[Historicalgasman]

Originally Posted by Landlockedpirate

Is the loss of power a loss in forward motion with revs still on the max or a loss of revs ?(i.e. you floor the accerator and the engine doesnt rev)

I havent got the rev guage connected yet, but the engine wasnt at full revs even with the throttle fully forward, but it would then jump to life with a wiggle of the throttle and you could feel the engine bite, on the way back in it was surging itself going from 7 knots up to about 16 without moving the throttle.

By the way I'm from St Helens!

[Pikey Dave]

Originally Posted by Historicalgasman

with the throttle fully forward, but it would then jump to life with a wiggle of the throttle and you could feel the engine bite,

Have a look at the throttle linkage, remove the air intake cover & make sure the throttle plates are fully opened with the throttle at WOT. If the throttle linkage is iffy, there might be something loose/broken & the plates could be sticking, but we're into the jumping around territory now

[Historicalgasman]

Originally Posted by Pikey Dave

Have a look at the throttle linkage, remove the air intake cover & make sure the throttle plates are fully opened with the throttle at WOT. If the throttle linkage is iffy, there might be something loose/broken & the plates could be sticking, but we're into the jumping around territory now

Cheers Dave, I'll have a look at that now. Do you know of any good online spares suppliers?

[Historicalgasman]

Originally Posted by Pikey Dave

Have a look at the throttle linkage, remove the air intake cover & make sure the throttle plates are fully opened with the throttle at WOT. If the throttle linkage is iffy, there might be something loose/broken & the plates could be sticking, but we're into the jumping around territory now

Linkage fine, plates full open on all cylinders at WOT just taken the carbs off, all looks very clean to me but as I said I am lacking in knowledge on this subject, is there something I'm missing?

Pics in my album.

[Chris]

Just to be clear you have opened the air Vent on the tank ? its a knurled brass screw usually and needs to be unscrewed when running to allow air into the tank.

[Historicalgasman]

Originally Posted by Chris

Just to be clear you have opened the air Vent on the tank ? its a knurled brass screw usually and needs to be unscrewed when running to allow air into the tank.

On my tank it is a plastic vent on top of the filler cap, when we first started running it wasnt, but I opened it up prior to the problem starting.

Could that have damaged the fuel pump?

[Poly]

Originally Posted by Historicalgasman

I work in Clydebank, I take it you mean I mark the nut in the centre and the rim of the prop and if the 2 don't line up off to Clydebank with the prop. Do you have the name of the company?

they are called something really imaginative like 'Clyde Propellers'. I think what you have described sounds right - basically the prop blades and the very centre are two separate parts bonded together by a rubber piece which protects the engine and gearbox from damage if it hits anything. But things like tangling rope round it can make the rubber part stop 'sticking' at high load.

However, as others have said if the engine went quiet or sounded like it was labouring rather than racing this is not the issue.