Issues with 1993 Mercury 40hp 4cyl outboard
Hi guys,
I am helping my brother out with his newly acquired boat that has a few issues to sort out.
When he first got it compression was down on cylinder 3 so we tore the powerhead off, reboard the block, and put it all back together with new pistons and rings. Now compression across all cylinders is good.
We went to start it and it will start with a good slash of primer fuel but wont idle correctly. To keep the engine running correctly you need to give it a fair amount of throttle.
I pulled the carbies off, gave them a good clean out and inspection and all looks ok from them so we put them back on with the same issue.
I am starting to get to the point where I am scratching my head so I thought I would put my hand out to the good people of this forum.
The only things I can think which could be causing this issue is:
1. The carbies are still badly out of wack
2. the timing is badly off
3. The reed's might be knackered and need replacing.
Obviously I would prefer it to be something like a timing or carby issue so I don't have to pull the whole engine apart again to get to the reed blocks but I just need to know what is wrong.
The boat is located in Minyama (Sunshine coast).
Thanks Guys, Help!
tim-o
Posts: 4657
Date Joined: 24/05/11
Cam timing haha
Cam timing haha. Id be startin with carb tune,
I am, as I've said, merely competent. But in an age of incompetence, that makes me extraordinary.
wydra
Posts: 24
Date Joined: 15/03/11
Cam timing??? I didn't say
Cam timing??? I didn't say anything about cam timing.
I know a 2-stroke doesn't have a cam or valves but it does have ignition timing that can be adjusted..
I agree the carbies could be the cause, just wanted to hear from some forum members who are either experts/pros in outboards or maybe even just have experienced the same issue in the past.
tim-o
Posts: 4657
Date Joined: 24/05/11
Haha, all good, I knew u
Haha, all good, I knew u didnt mean cam timing, I was being a SA.
I am, as I've said, merely competent. But in an age of incompetence, that makes me extraordinary.
scano
Posts: 1247
Date Joined: 31/05/07
Sucking air
Sound to me like there is a leak somewhere in the fuel supply and that it is causing the engine to have an air leak on idle.
a few questions.
if you squeeze the priming bulb does the primer stay or get very hard?
if so can you see any visible signs of fuel leak anywhere?
Finally, when u do have the engine running then I would be spraying something like brake or carby cleaner near the inlet manifold / carby gaskets.if the revs on the engine suddenly climb then there is a leak in one of the gaskets.
Leighwydra
Posts: 5
Date Joined: 29/04/13
Suggestions for Merc 40hp
Hi guys this is my boat. I've had it out on a couple of test runs. The carbies have been soaked, cleaned and re-installed and that made a huge difference with the idle. Now the other problem is the engine doesn't run well under load. You need hi revs to get it into gear otherwise it stalls and when cruising slowly it struggles until it gets on the plane. When on the plane it runs great!
Any ideas would be helpful
sstevee
Posts: 472
Date Joined: 15/11/11
PM sent mate
PM sent mate
Leighwydra
Posts: 5
Date Joined: 29/04/13
Still guessing
Not that I have noticed Steve. A little drips out the throttle shaft when I turn the primer on to start it.
Some fuel does spit out of the carbs when running, mainly the botton one.
The full lines have been inspected and seem ok, no cracks and securely fastened.
Paul H
Posts: 2104
Date Joined: 18/01/07
Where abouts does the fuel
Where abouts does the fuel come out of the carb, if its out of the fuel chamber it may be a stuck float in the carby fuel chamber. When i've seen this before a fair amount of fuel was coming out of the side of the carby fuel chamber.
There should be a screw on the front of the float chamber on the carby unscrew this and drain the fuel out, pump on the bulb lightly and pump some fuel through holding a clean white rag on the front where the fuel is coming out take note if any grit etc comes out. Then take off the fuel line where it goes into the float chamber and blow some air into the chamber through this again noting if you blow out any grit etc. May only need to do the one carby but would pay to do all of them whilst your at it. Reconnect the fuel line onto the carby and put the screw back in and see how you go.
Cheers
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