yamaha 55hp 2 stroke outboard problem.

**fisher tom** · 05-03-2006, 20:45

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.

Thanks fisher Tom..

**Why Worry Angling Charters** · 05-03-2006, 20:54

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** · 05-03-2006, 20:55

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** · 05-03-2006, 21:05

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** · 05-03-2006, 21:08

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?

The none return valve might be causing a restiction when under full load.

Cheers Steve

**fisher tom** · 05-03-2006, 21:50

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** · 05-03-2006, 22:14

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** · 05-03-2006, 22:50

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** · 06-03-2006, 09:17

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** · 06-03-2006, 11:21

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