Need help with 1984 mariner 40 hp

[dick_inc]

Hey there Guyz N Gull's,

I have a 1984 40hp Mariner outboard, it start's well (pull start)
has good comprishion both cyl, it rev's out in idle but when you put the hammer down some times it takes off and run's for about 100 mtrs then it drop's to about 4 knots still with the hammer flat down ???, could this be a carby problem as I have replaced the fuel with new fuel, and if it is the spark how or can I increase the spark, also I have a small crack in the gear box down by the prop, how hard is it to pull the old box off and put a new one on.

thank's for any idea's chris

[DavidT]

Chris,

I had the same problem with me 72 Model Evenrude, out of gear it would rev out like a maniace, but as soon as load was put on it in the water with soem backwards pressure it would die in the A$$

Later found out that it was a small crack in one of the fuel lines, as soon as it had to push petrol through at a rapid rate the crack expanded, i allways thoguht that thing used up too much fuel.

But your problem could be more Carbie relatedm well that is what it sounds like to me anyway.

I dont work on my own boat, but where i take it, he shows me everything that he worked on and what parts were replaced, i like to know these things in case something ever happnes to the engine out on the water i may have enough know how to get me out of trouble.

Cheers,

David

[NQCairns]

Just a guess, although it sounds like a fuel supply problem, somewhere hoselike is sucking air, or a very megre pump supply, vacume in tank. But what does it do after the 100m? Is the bulb no longer firm? what happens if you keep pumping the bulb within those 100m? nq

[dick_inc]

thank's guyz, NQ the fuel bulb stays firm I tried to pump it as we were going but doesn't seem to make any diffrence checked fuel lines seems to be fine. ???after the 100 mtrs it seems to lose rev's I first thought the coke float had stuffed up as once before when I had to pull the warm up lever up to get any rev's but not this time. >:(

[Fishin_Dan]

This was a little similar to some problems I had with my motor recently. 2 of the biggest issues with the fuel was that a) the bulb was leaking (dodgy even though brand new!) and b) the connection to the fuel tank was not sealing (dodgy connection - also brand new! And on a new tank!!!) Guess who got a brand new (tested) tank, fuel line, and bulb!!! ;D

It could also be your carbie gaskets. I had mine replaced (Water was found in the carbies), and she runs like a demon now!

[NQCairns]

Churchbro, bit of a long shot but have you checked the prop hub? I assumed your revs were actually dropping after the 100m but could you mean speed only?

Edit: Take no notice of the above I didn't read your last reply properly :P

If your bulb is tight you have a pump that works and a fuel line that doesn't leak. I would check the needle and seat or the float level, somehow that may be wrong. When/what do you have to do to get it back up on the plane again after the problem or is that it for the day?

[chemmy]

Hi

I have heard that old mariners are also called black anchors due to the fact that they always break down so my advice is to start saving for a new one or for a Yamaha

michael

[ba229]

It could be so many problems that you will have to work through them with us.

Fuel, electrical or mechanical is the question to start off with.

1.What ratio oil to fuel do you run? sometimes engines gag on oil after a short run. Does it clear itself up if you keep the throttle full open?

2.Does the engine RMP actually drop like nqcairns was suggesting? If it isn't it could be a slipping hub.

3.How long since the plugs were replaced?

Etc etc etc keep working with us and i hope it will be found

Regards

Alex

[dick_inc]

Hey guyz, after we slow to 4 knots that's it we don't go any faster, I have a feeling I may have found some thing, I had the motor running then pulled a lead off the bottom lead to the spark plug , the motor stopped , so I started it a gain and pulled the top lead off, the engine stopped spluttering #and ran smoother so I stopped the motor and pulled the end of the spark plug lead off and connected the wire stright to the plug head, it seems to run better, [smiley=2thumbsup.gif] will find out in about an hour as I'm going to take it for a run down the river. ( Just making sure the paddles are packed)

cheers chris.

p.s has any one got a gear box for this beast ??????
I have a crack in mine and need to get another , also is it hard to remove myself, I have some tool's and do work on my cars just never the outboard.

[blaze]

My thoughts are you have a blocked carbie on that cyc or low compression (as the motor warms there is more compression loss)
The Leg is easy to remove, most likely to be 5 bolts(one of them maybe under the trim tab) maybe also need to disconnect gear selector and then hope that it has been well maintained and the shaft is not siezed in the crank. Prob no help but keep posting and some one will come up with something
cheers
blaze
ps
A rough way to do a comp check is
remove plugs and earth out leads (some of these motors kick worse than a mule)
Now turn the motor over at starting revs (key or pull start) and hold your thumb over the plug hole, you will feel the diffrence if it is enough to cause a problem between the cycinders.

[dick_inc]

The beast is alive again when flat out for about 3km's then came back to ramp, I have changed the way the plugs are on the lead's I changed them to the same way the car ones are with a metal connector under a rubber sleeve, if any one can see any prob's with this please tell me now or for ever hold the peace.

Blaze the comp was checked out and have very good comp, it was the plug seemed to be making contact the after a while it would start earthing out to the motor.

now for the leg