Yamaha 55be (circa1991) service manual & general help with under-powered performance

[Neils6896]

Hi All,

I'm new to boating and just bought myself a little speed boat with a Yamaha 55hp outboard on the back. It's the 55be two stroke which i believe to be from around 1991.

I was wondering if anyone had a service manual form this or know's where i can get a copy?

Also i took it out yesterday for the first time and was a bit disappointed with only get approx 9 knots out of her, i was expecting somewhere nearer 30!!? It didn't seem to reach max revs and certainly didn't plain. Any common issues that might cause this or things i should check before throwing money at it?

[99yam40]

always start out with checking compression , spark, and timing to make sure they are good.
spark tester or a timing light should show if spark is getting to each plug

if all of that is in spec then you start looking for fuel problems.
too little or too much fuel will cause problems'
fuel pump leaking, carbs not filling properly, jets or passages plugging up

[TownsendsFJR1300]

How big is the boat, length wise?

.

[Neils6896]

How big is the boat, length wise?

.

Hi Scott, it's a 15 foot Simms Super V.

[Neils6896]

always start out with checking compression , spark, and timing to make sure they are good.
spark tester or a timing light should show if spark is getting to each plug

if all of that is in spec then you start looking for fuel problems.
too little or too much fuel will cause problems'
fuel pump leaking, carbs not filling properly, jets or passages plugging up

Thnask for the advice! I'm cool with most of that but how do i go about checking the compression? what should i be looking for and how do i physically do it? Many thanks.

[boscoe99]

https://www.boats.net/product/yamaha/LIT-18616-00-43

[boscoe99]

Take it to a Yamaha mechanic would be my suggestion. Hopefully, he will let you look over his shoulder and learn something while he goes about his business.

[99yam40]

Thnask for the advice! I'm cool with most of that but how do i go about checking the compression? what should i be looking for and how do i physically do it? Many thanks.

just like on any other motor, pull the spark plugs, install compression gauge, pull the kill switch to kill spark , and then spin the motor over until the gauge does not go up any higher

rule of thumb is cylinders should be within 10% of each other

[Neils6896]

https://www.boats.net/product/yamaha/LIT-18616-00-43

What's that mate?

[99yam40]

looks like a part number for a Yamaha service manual for your motor maybe

[Neils6896]

Okay.... on investigation it looks like i might have a an oil mix v spark plug issue!?!? I got hold of a service manual which seems to suggest i should be using 100:1 mix with NGK BR8HS-10 plugs. Is that correct for the UK?

Others seem to think I should be running 50:1 mix but if that's the case would i also need to change the plugs for NGK B8HS-10?

TIA.

[99yam40]

the R is for resistor, back in the old days for autos they were to help reduce the noise in the radio .
not sure what they are for in a Yamaha outboard.
50 to 1 will protect the shiny internal surfaces better during none running times a lot longer

[boscoe99]

Okay.... on investigation it looks like i might have a an oil mix v spark plug issue!?!? I got hold of a service manual which seems to suggest i should be using 100:1 mix with NGK BR8HS-10 plugs. Is that correct for the UK?

Others seem to think I should be running 50:1 mix but if that's the case would i also need to change the plugs for NGK B8HS-10?

TIA.

What is the identity of the service manual? The CV55E SM indicates 50/1 for the fuel to oil ratio. B8HS-10 spark plug.

[boscoe99]

What is the complete model identity? Will begin with the number 6? Should be on a placard on the side of the motor. On the clamp bracket.

[Neils6896]

here's the model number and the service manual i found.