Yamaha autolube idle /low speed issues

Bren91 · 18 January 2016, 20:02

So I have a 60hp autlube Yamaha 1994 engine on the back of my rib.

I bought the rib as a bit of a project and am loving it so far.
Having issues with low speed anything below say 10 knots.

When I got the rib the engine would not run at all in the tilted down position, I have since pulled and cleaned the carbs and replaced what was needed and has sorted that problem.
Since taking it out (trial and error days) it wil struggle and cough and splutter while low speed.
I pulled the carbs again to replace some gaskets as I wasn't happy.
Spark plugs have been changed too as well as adjusted idle mixture screws to recommended settings.

Had it in the water today and she starts on the button and idled fine.
As soon as I'm underway and say 4-10 knots it almost feels like it's surging and spluttering coughing.
As soon as I get her up on the plane and open it up she's fine.
Apart from the shocking fuel consumption of .8L to the mile she's great.

Does anyone have any clue as too what I should be checking.
Quite mechanically minded but this has me stumped.
Next I'm
Thinking to do a timing test and really sort these carbs out as regards to tuning
But other than that any ideas??

Thanks Brennan

A1an · 18 January 2016, 20:21

Do you have a tachometer fitted?

I've had 3 yamaha 3cyl models, 2 x 60hp and 1 x 75hp, all have sounded rough until 2100 revs then they seem to smooth out.

Bren91 · 18 January 2016, 20:32

Ah ok. It just seems to uneasy and spluttery??
I do have a tach but it doesn't work. Another issue I'm tracing

A1an · 18 January 2016, 21:24

Just another thought, have you checked the rear skin on the fuel pump?

These skins can perish/tear and flood the lower cylinder with unmetered fuel.

kawasaki · 18 January 2016, 23:40

Mate, you seem to know what you are doing ref engines and two strokes. Imagine your lump was a two stroke motorcrosser. It might 'tickover' ok then fuss about a bit whilst getting to revs it likes, as they do. If She idles ok and gets up on 'main jet' ok dunna worry. Two strokes as you know don't like it when not underload. I would leave well alone for now and run Her for a few hours. 1994 eng, is quite basic technology. As a rule of thumb though, if you have low speed/revs prob, it is a problem with the 'low tension' side of the ignition system, ie the stator or coils therein. Plus anyway, what are you doing at 4-10 kts? Pedal to the metal Mate!!

beamishken · 18 January 2016, 23:48

Got all the symptoms of a fuel pump diaphragm as a1an says that would be my first place to check

JohnsonV4 · 19 January 2016, 08:20

One other thing to check with these twostrokes. Make absolutely sure that carbs work in sync with the timing. Plus check that the throttle-valves are fully closed and open all at one. very diffycult to achieve but crucial. If one throttle hangs open just a tad at idle , it will create a lean situation and cough!!
And does the carbs have idle jet screws? If so check if there all in the same spot, turns wise.

dave3235 · 19 January 2016, 10:19

Quote:

Originally Posted by JohnsonV4

One other thing to check with these twostrokes. Make absolutely sure that carbs work in sync with the timing. Plus check that the throttle-valves are fully closed and open all at one. very diffycult to achieve but crucial. If one throttle hangs open just a tad at idle , it will create a lean situation and cough!!
And does the carbs have idle jet screws? If so check if there all in the same spot, turns wise.

Hi all

You could check the choke may be it's staying on a bit.Had similar simptons to that using lots of fuel and sputtering at low revs,just a thought though.

Bren91 · 20 January 2016, 08:08

Hmm thinking about it, it does sound like a fuel pump diaphragm. Will try and get some time this arvo and pull her apart.
AS for going slow, the harbour master and the yatchies down here always have something to say about going to fast lol.
The coils ill check aswell, definatly getting spark from all 3.

Will double check the choke staying on. altough at high revs she would just cut out.
Fingers crossed its just a gasket in the fuel pump.

Thanks all for the imput

A1an · 20 January 2016, 20:59

If its just a gasket give me a shout, I've probably got one in my "bits" box.

dave3235 · 20 January 2016, 22:38

Quote:

Originally Posted by Bren91

Hmm thinking about it, it does sound like a fuel pump diaphragm. Will try and get some time this arvo and pull her apart.
AS for going slow, the harbour master and the yatchies down here always have something to say about going to fast lol.
The coils ill check aswell, definatly getting spark from all 3.

Will double check the choke staying on. altough at high revs she would just cut out.
Fingers crossed its just a gasket in the fuel pump.

Thanks all for the imput

Hi

My engine has a primer choke may be that's why I found you could still give it full throttle.