yamaha 55hp 2 stroke outboard problem.

[fisher tom]

Hi Guys.
I have a 55 yamaha that runs well in the drive and runs well in the
water until you go take off, at first it goe's well then as it is plaining it starts to splutter and ends up at 6mph with full throttle it is very spluttery but if you ease it back it seams to run well but slow. If you try to go faster it picks up a bit and then splutters again. I have had the carb cleaned, engine and electrics checked by a mechanic and he give it thumbs up and it only run well for 100meters with the same problem. The problem only halpens when the engine is under load.


It's year is aprox 1980
new gearbox, new drive shaft and new impellor.
A small fortune spent and still no joy

Can anyone help as I am fed-up with it.:nonono:

Thanks fisher Tom..

[Why Worry Angling Charters]

Just wondered is the tank breathing properly? Have you dumped the fuel and bought new?Check all your fuel lines to make sure you have none that have a pinch in them.It definately sounds like a starvation of fuel or as I said even bad fuel.
Ron

[Davy Holt]

Hiya,

check the fuel pump.. sounds like it could have a pin hole in one or both of the neoprene sheets in the pump.

[kababusmaximus]

check that your advance and retard is working freely mine was sticking a bit ago on the drive or in a tank ran as sweet as a nut under power set off then died then played with throttle would run better but lumpy only way i spotted it was i took of the cowling with the engine of moved the throttlethrough the forward gear and found the throttle opening but the advance was sticking give it a go hope it helps kababus

[fishy Finger]

Hi Tom

I would second that. had a similar problem with a Yam 30 a couple of years ago, get the fuel pump complete repair kit that should sort it.
Another thing to try first. Is the fuel bulb getting hard when you pump it?:uhuh: The none return valve might be causing a restiction when under full load.

Cheers Steve

[fisher tom]

Hi guys.
Thanks for the help.
Can you tell me how to check the advance and retard?
Also is it easy to fit the new neoprene sheets into the fuel pump?
I fitted a new fuel bulb but it did not work but getting a new tank and lines tomorrow to try.
Thanks. Fisher Tom.

[ChrisP]

Get out on the water with a mate and hold the tank above the engine, have a bit of a run and see if the engine runs normally. If it doesn't it is in the ignition system. If it does drop the tank to it's normal position and try a run again. If it splutters it is the fuel sysem. First thing check is there are no nicks in the 'O' rings in the pipe connectors. This can let in air under load. I have a clear glass inline filter that I fit inside the engine cowling to check if any air is entering the system.

If these are looking good the next thing is like Davy suggests, a pinhole in the fuel pump diaphram\s.

To remove the fuel pump undo the two hoses, then the 2 X 10mm AF bolts and the plastic assembly should come away from the block. Undo the 4 cross head screws and the block should split apart. Hold the two diaphrams up to a light and stretch them. Any light you can see is a hole and the diaphram is goosed. Replacement is the reverse of removal.

Let us know how you get on, there are other things to cause this but fuel is most likely. Only adjust one thing at once, ie dont play with the engine timing and fuel system. it makes it a lot easier to trace the fault.

[fisher tom]

Thanks Chris.
New tank and hose to fit tomorrow and I will check
the diaphrams. Then take it for a run with the fuel tank
levels test and get back to you tomorrow evening.
Thanks again mate.

[boycey 32]

hi i had the same plobrem with my 90 it was down to the oil pipes.enough oil getting to engine when ticking over or reving up but all of a sudden when under load in the water it would basically slow down to about 5 to 6 knots and if i tried reving it then the engine would just jump about and shudder like mad but it would run fine for parts of the trip then it would happen again
hope this helps
boycey 32
try mixing the oil straight into the fuel tank and then try it

[MarieK]

One last thing - remember to actually bolt the engine on the boat before you set off! I know you are very safety conscious and would never let such an oversight go unnoticed but you never know! I was talking to a boy last weekend who was flying around in his brothers boat when all of a sudden the engine came off!!

All the best
MarieK

[Simon F]

Hi Guys.
I have a 55 yamaha that runs well in the drive and runs well in the
water until you go take off, at first it goe's well then as it is plaining it starts to splutter and ends up at 6mph with full throttle it is very spluttery but if you ease it back it seams to run well but slow. If you try to go faster it picks up a bit and then splutters again. I have had the carb cleaned, engine and electrics checked by a mechanic and he give it thumbs up and it only run well for 100meters with the same problem. The problem only halpens when the engine is under load.


It's year is aprox 1980
new gearbox, new drive shaft and new impellor.
A small fortune

I had the same symptoms ( not necessaraly the same problem ) with an Evinrude 50 HP of similar vintage.

It ran great in the drive on "flushing muffs", yet in the water there was no power at all. It turned out one that pot was not operational at all, in the end I needed a new head. Simple test though. With it running in your back yard, just disconnect one spark plug at a time, see if it changes the way it runs. If it doesn't that one is not firing. If it does - thats not your problem.

[fisher tom]

Hi Guys.
Only doing one thing at a time. I have tried the test with the spark plugs ang it change's the way it runs and its sparking well on both plugs.
Today I disconected the fuel pump from the engine without opening the screws that hold it together and leaving the fuel lines connected. Then I pumped the
fuel bulb and petrol leaked out the screw holes in two places, Then I took it apart
I pushed my finger into the middle of the rubber and noticed tiny bubbles coming through the middle of the rubber(neoprene sheets). The rubber is stuck to the metal like glue I have not taken it of to see if it has any holes.

Are the neoprene sheets ment to be Fuel tight?

Is there any point in looking for holes since it leaked before I opened it?

Thanks Fisher Tom.

[ChrisP]

The neoprene is what pumps the fuel, it only operates on about 2psi. Sounds like you need new ones. If you get a service kit for the pump you should find the preblem gone.

[fisher tom]

Hello again
Got fuel pump rebuilt with all new gaskets and still have the problem.
But the engine is running better as it does not stall when you take it out
of gear (it did it all the time before fuel pump rebuild).
Now it is still spluttering when you try to go faster than 8mph(runs fine at 6mph no splutter) So I tried the new tank+ line and it made no difference.
The only strange thing was I have an electric choke on the key switch and when you are spluttering allong (flat out) if you put the choke on for a fraction of a second the engine would cut out for a second and then pick up the revs and go faster and if you continue to do this every 3 seconds the speed would pick up to about 25mph and as soon as you stop choking it it would start spluttering again and 8mph.
I do not know what that means but it must be fuel.
Can you tell me what to try now?
Fisher Tom.

[ChrisP]

Get a can of WD40 and squirt it on the joint between the carb and head whilst the engine is running. Does the engine pick up as you spray it?

[fisher tom]

Sprayed all around the gasket and did not make any difference to engine tone
and no sign of bubbles.(Running with muffs)
This problem only occurs when under steam and in the water
is this when I should spray it?

[ChrisP]

It sounds like you have an air leak on the fuel side or something in the carb is not letting enough fuel through.

The WD 40 was to see if there was a leak at the inlet manifold, if there is the engine revs will chang as it burns the WD.

2 things now, you said your carb has been rebuilt, is it adjusted right, is the float valve set right and not sticking. Are the jets, fuel passages clear?

Second thing, take the fuel pipe off the side of the carb, between pump and carb. Replace it with clear pipe and take the boat out, if you can see bubbles in the fuel you have a leak somewhere that is allowing air in when the engine is under load.

Sorry for all the checks but it is really hard to diagnose without being able to see and hear the engine.

[fisher tom]

Hi Chris.
Leaving it back to the Guy who
originally fixed it. He said the same as
your - self , so maybe he will fix it this time.:uhoh:

Thanks Chris and everyone who helped:notworthy
Would be lost without the help!
Let you guys know next week if its fixed.

Thanks again. Fisher tom.

The 40 4stroke is on the horizon

[scottishmotorman]

Hi Guys.
I have a 55 yamaha that runs well in the drive and runs well in the
water until you go take off, at first it goe's well then as it is plaining it starts to splutter and ends up at 6mph with full throttle it is very spluttery but if you ease it back it seams to run well but slow. If you try to go faster it picks up a bit and then splutters again. I have had the carb cleaned, engine and electrics checked by a mechanic and he give it thumbs up and it only run well for 100meters with the same problem. The problem only halpens when the engine is under load.


It's year is aprox 1980
new gearbox, new drive shaft and new impellor.
A small fortune spent and still no joy

Can anyone help as I am fed-up with it.:nonono:

Thanks fisher Tom..


Hi Tom. Try This

1 - Check no water in fuel tank
2 - Ensure fuel connectors fit and the fuel bulb goes solid once primed - genuine yam pars are best.
3 - Prime bulb. If it appears to keep pumping fuel, check the o rings on the fuel filter. Then check to see if there is fuel running from the carbs when squeezing fuel bulb. If there is suspect a float height or shut off pin problem. If not this, back off the two bolts holding on fuel pump and squeeze bulb if fuel pours from central hole - diapragm is gone.
4 - Start the engine and run in gear with the lid and carb baffle removed. Run at speed and see how much fuel is being is being drawn through the carbs. If it is fuel starvation caused by a blocked jet there will be a noticable difference. The carb may have to be stripped by a competent outboard mechanic.
5 - Hopefully no one has fiddled with the mixture screws or the butterfly settings.

Now the electrics

1 - Check/Replace the plugs
2 - Clean the plug caps. The bottom cap has a habit of shorting out against the bracket which holds the lid in place causing power loss. Also causes fire if this happens with a carb or filter leak,
3 - Look at the wires entering the stator plate, they have a habit of breaking on the older 55s. Again you will need a competent mechanic to replace if broken.
4 - Make sure the stator plate is moving freely between the timing stops they can seize up
5- Always handy to have a spare ignition coil. They dont often go wrong, but can break down under load.
6- Start engine on top cylinder only. Then bottom cylinder only. this will tell you if both are firing.

Thats your fuel and electrics checked.

Ignition timing.

1 - If the engine was running fine before the problem developed there should be no need to adjust. Unless you know what your doing - dont touch.

Hope all this helps

[Cascars]

The thread is now almost 3 years old so |I would hope he has got the problem sorted by now. If not he has probably sent it to the scrapyard by now.
Good advice though for your first post. Welcome to WSF scottishmotorman:thumbs:

[TomBettle]

Nice first post Scottishmotorman.
On a par with the advice that ChrisP used to give and Nos4r2 does now.

Excellent, hope the guys engine is still operational today.

Tom