Power loss

[Peter Nelson]

Hi All

I have a 2 stroke Yamaha outboard 70hp and when coming in from a mornings fishing it decided to loss power and basically cruise at low speed.

I took it up to about 3900rpm and all of a sudden it dropped down again.

I took off again after a few minutes and it seemed to run ok for a minute or so, which i was right next to the boat ramp so i decided to take it back in as the tide was running out pretty hard.

A few questions:

1.It's possibly a fuel problem, I noticed where the fuel line clips onto the motor the seal is fairly perished, could this be sucking air?

2. If it was overheating do they have an audible alarm and can i test it some how?

3.How much oil should it be using? I havn't had a boat for a while and I recall my old boats mercury 75hp using more oil.

Any help or opinons would be greatly appreciated.

Cheers

 

 

[raging]

Check your manual to see if you should hear the alarm on start. 

If alarm is broken, motor could be going into limp home mode due to overheating or a lack of all. 

Another possibility is fuel pump leaking

[rickmarlin62]

I had 60 yammie that did same..take your carbies off drop the bowls off and clean them out..its not hard on yammies..I put water separator filter on then had no more probs..the crud in bowl swirls around and gets sucked onto main jet  then when yo back off it drops away..hit revs again happens again...rick

[jeffb5.8]

Also when it happens is the fuel bulb soft or hard?

Start with changing filters and the fuel line if it's perishing at the joint.

Fresh fuel?

when was the engine last serviced, did they change the water pump impeller, has the thermostat been check or replaced?

jeff

[Flickn Mad]

Hey Peter, how old is your motor? I have a 95 70hp yammie.

If it goes into limp mode it should shake and carry on when you try and increase throttle. 

When I first got mine, second hand it did similar to yours on a run back through the heads on the shoalhaven, not a place you want to loose power. Motor dropped all power before getting its breath and having another go. Found one spark plug badly eroded. Replaced plugs and problem never returned. 

Rick is probably right, but I would start with the easiest items first. 

Plugs , leads, filters. If the boat is new to you but you have no service history it's probably not a bad idea anyway. 

Let us know how you get on.

Also, I did seize mine a few years later when a blade of the impeller inexplicably decided to let go, it had similar Simptoms. Heat up, get tight then when idled cool down, loosen up again and repeat until I shut it down at the ramp and it locked solid. Hope this isn't the case for you. 

[Peter Nelson]

15 hours ago, rickmarlin62 said:

I had 60 yammie that did same..take your carbies off drop the bowls off and clean them out..its not hard on yammies..I put water separator filter on then had no more probs..the crud in bowl swirls around and gets sucked onto main jet  then when yo back off it drops away..hit revs again happens again...rick

Cheers Rick ill give that a go.Did you need new gaskets or seals?

[Peter Nelson]

6 hours ago, jeffb5.8 said:

Also when it happens is the fuel bulb soft or hard?

Start with changing filters and the fuel line if it's perishing at the joint.

Fresh fuel?

when was the engine last serviced, did they change the water pump impeller, has the thermostat been check or replaced?

jeff

Hi Jeff

I didn't check the bulb I was out by myself and only had getting beck the ramp on my mind.

Ill definitely change the filter and fuel line.

3/4 of the tank was a few months old and topped up the rest that morning.

I've had the boat for about 4 months and was serviced before I got it, definitely new filter and plugs and fresh grease,didn't get the receipt but the previous owner said the impeller was done(hope it was).Not sure about thermostat, is that something that gets done on a service?

[Peter Nelson]

3 hours ago, Flickn Mad said:

Hey Peter, how old is your motor? I have a 95 70hp yammie.

If it goes into limp mode it should shake and carry on when you try and increase throttle. 

When I first got mine, second hand it did similar to yours on a run back through the heads on the shoalhaven, not a place you want to loose power. Motor dropped all power before getting its breath and having another go. Found one spark plug badly eroded. Replaced plugs and problem never returned. 

Rick is probably right, but I would start with the easiest items first. 

Plugs , leads, filters. If the boat is new to you but you have no service history it's probably not a bad idea anyway. 

Let us know how you get on.

Also, I did seize mine a few years later when a blade of the impeller inexplicably decided to let go, it had similar Simptoms. Heat up, get tight then when idled cool down, loosen up again and repeat until I shut it down at the ramp and it locked solid. Hope this isn't the case for you. 

The motor is a 2006.

When it lost power and when I throttle up again it was smooth, no coughing and shacking.

Yeah i hope mine doesn't end up like that, were you getting temp alarms?

Cheers

[Flickn Mad]

1 hour ago, Peter Nelson said:

The motor is a 2006.

When it lost power and when I throttle up again it was smooth, no coughing and shacking.

Yeah i hope mine doesn't end up like that, were you getting temp alarms?

Cheers

No. I think because it was the bottom of the three pistons which seized and the temp sensor is located next to the top cylinder it didn't go off. 

[jeffb5.8]

I never trust a seller about servicing unless they can produce a receipt, to many wannabe Mech out there, change the easy to see things and don't worry about the harder things.

i bought a 2007 25hp and the owner said it was recently serviced, no receipt cause like everyone he had a mate who was a marine Mech, I bought the outboard budgeting on it needing a service and then took it straight for a service, turns out the thermostat was missing and the impeller was old and worn, but it did have new plugs and fuel filter.

Is your oil injected or pre mix as maybe that's playing up, is it using the normal amount of oil?

Edited September 21, 2017 by jeffb5.8
spelling

[Fab1]

14 minutes ago, jeffb5.8 said:

I never trust a seller about servicing unless they can produce a receipt, to many wannabe Mech out there, change the easy to see things and don't worry about the harder things.

i bought a 2007 25hp and the owner said it was recently serviced, no receipt cause like everyone he had a mate who was a marine Mech, I bought budgeting on it will. Red a service and then took it straight for a service, turns out the thermostat was missing and the impeller was old a worn, but it did have new plugs and fuel filter.

Is your oil injected or pre mix as maybe that's playing up, is it using the normal amount of oil?

I think the best advice without seeing it ourselves we can give him is to take it to a reputable mechanic for peace of Mind.

[rickmarlin62]

unless the gaskets break you should be able to leave them in place and reuse..rick

[Peter Nelson]

12 hours ago, jeffb5.8 said:

I never trust a seller about servicing unless they can produce a receipt, to many wannabe Mech out there, change the easy to see things and don't worry about the harder things.

i bought a 2007 25hp and the owner said it was recently serviced, no receipt cause like everyone he had a mate who was a marine Mech, I bought the outboard budgeting on it needing a service and then took it straight for a service, turns out the thermostat was missing and the impeller was old and worn, but it did have new plugs and fuel filter.

Is your oil injected or pre mix as maybe that's playing up, is it using the normal amount of oil?

It's oil injected and when compared to a mercury I used to own it uses a lot less, previous owner said he had the oil sender recently replaced

[rickmarlin62]

the two things that ive seen make a yammie do that is crud in bowl which will block a jet then when you back off it swirls around till next time it passes the jet and blocks again..in between it seems ok..no2 is plug leads coming off but then it runs rough till you shove it back on...if you don't have good filter its a certainty that you will get dirt or water in bowl..also if not run all the time unleaded fuel dries out in bowl and leaves deposits..every carby I have pulled apart in last couple of years on boats or bikes has crud in them..rick

[rickmarlin62]

I run the same water separator filter and havnt had a prob since...rick

[Peter Nelson]

4 hours ago, Trailcraft43 said:

I run 1 of these filters on the boats.

it seperates crud from fuel and water can be drained away.

has a canister filter that's changeable.

good insurance in my eyes.

you don't want a motor konking out crossing a bar or racing a storm home.

I  think i'll get one. I have got one that looks like the type used on your car, no bit on the bottom.

Cheers

[Peter Nelson]

Good news no more power loss(hopefully).

Cleaned and flushed fuel filter and found a fair bit of crap in there.

Didn't strip carbies off and clean bowls as i found some sort of electrical connection that didn't what to budge so i didn't want to force it.However i did remove the drain screws on the bowls(except the bottom one as i couldn't access it) and pumped fuel out of them to hopefully flush them.

I have gone for 2 decent length trips and no problems so hopefully the gremlin has disappeared.

Thanks again for all the replies and help.

[Flickn Mad]

YAY! Glad to hear you got to the bottom of it without any drama or expense.

I am about to post some photos of my head when I pulled it apart on a post just above.

All I can say is make sure you flush the yammie well.

 

Good luck.

[rickmarlin62]

you should flush every motor well   seem to be hearing lots of people having salt buildup probs lately...5 mins of your time makes a big difference to engine longetivity..rick