1980 8HP Yammie problem

[BassMenace]

Hi all

1980 8HP Yamaha outboard. Was running great until a month or so ago.
The problem is that even at full throttle it was running as though it was on 1/4 throttle. If you left the throttle the motor would then cut-out. It should be noted that in neutral if you revved her she seemed to get to top revs. Even in neutral it would slowly die if no throttle was applied.

I replaced the plugs, no change.

I cleaned the carb and adjusted the idle screw, she idles beautifully now and seems to be revving up a lot higher in neutral. I checked the plugs again since my test run after replacing them and the top plug was clean, the bottom one had some black reside (muck) on it.

The problem now is that as soon as I engage Forward, she cuts out.

Is it maybe the idle screw?

If it's a timing or compression issue how would I go about checking that?

Thanks in advance.

[99yam40]

test the compression with a compression gauge
check Timing with a timing light to make sure it is advancing properly

The timing light will also indicate if spark is being dropped to plugs if you hook it to them individually

Compression,spark, and timing if they are all good then you are left with a fuel problem
Clean carbs and adjust as service manual calls for
Check fuel pump for leaks

do not rev the motor in neutral like that it proves nothing and can hurt motor,
It takes more fuel to run under load

[BassMenace]

Thanks 99yam40

I checked the fuel pump and no leaks, will check the rest.

What fuel would you recommend for these older units? Here is South Africa we have unleaded fuel or lead replacement fuel. Both 95 octane.

[99yam40]

I do not think it would really matter which you used as long as it is fresh and clean along with good marine 2 stroke oil
most were designed for 87-89
the 95 will burn a little slower

[BassMenace]

Great thanks 99yam40.