eratic idle on my Mercury 40 classic??

[bryan160]

I have run my new (second hand) Mercury 40 hp classic 4 cylinder oil injection outboard, it starts first time ans runs well, however the idle is eratic, I set the idle screw to mkae it tick over just right,then when I rev it using the fast idle lever it often idles to high when return the fast idle lever , then after a few minutes it will return to normal ide, but sometime stalls.
Does anyone know what this might be, the engine has been sat for a month or so, will it just need a good run??

Cheers Bryan

 

[Kawasaki]

You could try a good run.
What year is She?
I know the symptom you refer to.
I have in the past had to resort to stripping all the carbs, neww seals o rings and gaskets on one Merc before it would perform properly.
Mind you She had sat for nearly 2 years with no protection.

 

[RobWales]

Carbs could well be what they call gummed up!
Two strokes that have not been used for a while tend to act like this if all the fuel in the system is not used up.
Petrol/2 stroke mixture is left in the carbs and the petrol will eventualy evaporate off leaving the 2 stroke oil to go like a gummy/varnish over everything
Sugges Halfrauds carb cleaner(be aware naughty stuff!)strip carb and spray every orofice etc..................Good luck.

 

[Lakesailor]

[ QUOTE ]

Petrol/2 stroke mixture is left in the carbs and the petrol will eventualy evaporate off leaving the 2 stroke oil to go like a gummy/varnish over everything


[/ QUOTE ]
But it's an oil injection motor. So it'll be pure petrol in the carbs.
I would assume that the carbs have been messed with and check all the float levels. Balance the idle screw settings. (try screwing one in fully, counting the turns and then return it to the start point. Then check the others are all the same. If it's the wrong setting remember to adjust them all equally. Often the basic setting is one and a half turns out from fully home, but check first with a Mercury dealer)
Air leaks between the carb and motor could cause erratic high tickover. If the carbs use diaphragms there may be splits or have pinholes in them, but that would possibly effect starting, which you say is OK.
The fast idle controls themselves may be sticky, are all the linkages free moving?

Next think. Visit http://forums.iboats.com/forumdisplay.php?f=25
If you can't find an answer here, there isn't one

 

[andyball]

[ QUOTE ]
But it's an oil injection motor. So it'll be pure petrol in the carbs.


[/ QUOTE ]


true of course - tho the gummy residue can still be a huge problem. Most carb cleaners don't touch it once it's set hard.

I found something that did ( hmm memory fails, but was from a wood-finishing supplier in 5l cans) but made o rings/seals all floppy, so a major strip-down requ'd.

 

[Kawasaki]

Good reply Lakey.
braynw. If You haven,t done or are not familiar with the task ahead, try to find a bod that is/has.
I,m all for a bit of DIY, but stripping and rebuilding a 4 carb Merc set up is ok . If you know what You are at withcarbs and suff.
There are seals , o rings and Diaphragms to check.
You can do the basics Youself.
Drain each float bowl.
There will be a drain plug/screw.
If You feel confident enough, remove the float bowls.The main jets and the pilot jets.
Access to an air line would be good to blow through the carb body.
The pilot air jet is important at the tickover/ low end of the rev scale.
Set as the Man says.
I would strip and clean the carbs as best You can.Reassemble. If you see any bits that need obvious replacement ok stick new uns in.
If she starts and runs ok at the top end then there is not too much wrong.
Tiss really quite basic. Strip and clean and reassemble and check all linkages are free and balanced. IE all opening and closing at the same time.
What I,m trying to say, in a round about sort of way this AM!
Is have a dabble but don,t get too involved if it,s the first time for You to mess with carbs etc.
If the basic strip/clean/reassemble doesn,t cure then there is a seal o ring type prob.
Gunge and crud in the carbs is usally 90% of the prob.
The fast idle lever.
Make sure it "sits home" properly.
Get someone else to tweek it whilst You eyeball at the eng end.
You will then see how the linkages work also.
As said if She sarts and runs and "revs out" ok.
There should be no probs with, eng crank seals and diaphrams and suck like.
Bet it is a combination of gunge and balancing and the fast idle return bit.
Good luck!
Oh! again how old?

 

[jfm]

Agree all the comments about checking cleaning carbs and throttle linkages. But IIRC some early "oil injection" 2 strokes injected oil into the fuel line early in the system, ie before the carbs. Obviously it's all cleverer than that on newer motors, but I wonder if the Merc 40 injection was old tech stuff? In which case carbs are likely to be a gummed/oiled up