8HP Yamaha missing at high revs

[holbecka]

Hey Fishraiders,

Any help on this one is appreciated. I was recently given a 3.3.m tinnie and purchased a second hand 8 HP Yamaha outboard. I'm not sure of the manufacture date, however, its safe to say that it's probably circa 1990. I know very little about outboards (this being my first). I took it for its first outing over the weekend and noticed three things in need of addressing. Whilst the motor starts without hassle, after about twenty seconds at the highest revs it sounds as if its missing or wants to cut out. It revs then cuts out, revs then cuts out and so on. This doesn't seem to happen at lower revs or speed. I'm not sure if this is releated, however, it does blow a fair bit of whiteish coloured smoke and I've noticed oil droplets in the water as well. I'm using a feul mixture of 50:1 presently. I wondered if this mixture may be too rich given the issues. Any advice or sharing of knowledge appreciated big time. Thanks in advance.

Andrew.

[The Incredible Hull]

Are you using new fuel? I.e. did you pour out the old fuel?

50:1 sounds about right, a bit of white smoke is ok, you'd rather be running rich than to burn out your motor.

Maybe try replacing the spark plugs.

[holbecka]

Thanks Incredible Hull,

Brand new feul, oil and spark plugs. Someone suggested the "Feul mix screw" may need adjusting?

Andrew.

[The Incredible Hull]

Thanks Incredible Hull,

Brand new feul, oil and spark plugs. Someone suggested the "Feul mix screw" may need adjusting?

Andrew.

That sounds like the Fuel\Air Mix screw? I played around with that on my motor bike, I wouldn't suggest fiddling with it too much. Look at other options.

In some previous posts... check the "Breather Cap" on your fuel tank (hopefully you have one). On my tank, the breather cap itself is on the Fuel Cap lid where you pour fuel in. Mine is a screw with a rubber washer. Make sure it is unscrewed so air can get in.

EDIT:

Perhaps have a read of this post too, it may be related:

http://www.fishraider.com.au/Invision/index.php?showtopic=63751

Edited June 18, 2012 by The Incredible Hull