Outboard mystery.

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bigman1

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HI,i have year 2000 40hp mariner manual start outboard, i bought it 3 months ago ran nice on demo. no smoke no noise,its 2 stroke,now this is the mystery it wont turn over with plugs in,with plugs out turns over fine,what is causing abnormal compression?i thought perhaps oil from petrol. flushed it out with pure petrol,no differance,online advice for clearing 2 stroke hydro lock is remove plugs spin over and should clear. But to go from nicely running engine to wont crank wreck is hard to take. It was stored in dry cupboard for 3 months,no abuse nothing,i cant work this out!
I read online about outboard whoose start in gear cable had broke,but if this was causing this trouble surley it would still bind with plugs out? if somone can help please.
 
Have you been running it since you bought it or was this locking-up apparent on the first time you tried to start it so you removed the plugs to see what happened?

If this is the first time you have tried to start it I suspect that you are simply not using the right starting technique and the engine is getting "stuck" just before maximum compression and you are not pulling it over TDC.

Try starting with one spark plug in and connected and the other out. If you can turn it over with one plug it will probably start. You can then try with both plugs in once you have mastered the technique.

Richard
 
RichardS said:
Have you been running it since you bought it or was this locking-up apparent on the first time you tried to start it so you removed the plugs to see what happened?

If this is the first time you have tried to start it I suspect that you are simply not using the right starting technique and the engine is getting "stuck" just before maximum compression and you are not pulling it over TDC.

Try starting with one spark plug in and connected and the other out. If you can turn it over with one plug it will probably start. You can then try with both plugs in once you have mastered the technique.

Richard
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If you turn it over with the plugs out, make sure you have plugs connected to plug leads or you can damage coils
 
Hi

Have you changed the plugs ?. are the new ones the same length ?

Try rotating the engine slowly i.e not by pulling the starter cord, see if you can take the enginge over TDC slowly

Good luck
 
seadog30 said:
Hi

Have you changed the plugs ?. are the new ones the same length ?

Try rotating the engine slowly i.e not by pulling the starter cord, see if you can take the enginge over TDC slowly

Good luck
Click to expand...

I was also wondering about the plugs ..... they should be NGK BP8HN-10 , which are 12.7 mm reach. To prevent the engine being turned they would have to have been changed for longer reach (19mm) plugs after the demo run
 
bigman1 said:
The plugs have not been changed same ones as on demo run.
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then i go along with richard in #2

bigman1 said:
If the reed valves are stuck or fused closed there is no where for the compressed air to go or escape.
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The reed valves are between the induction manifold and the crankcase. They open to allow air and fuel to be drawn into the crankcase as the piston rises but close when the piston descends to retain the mixture and pressurize it for its eventual transfer to the combustion chamber.

They dont open to allow the compressed air/fuel mix to escape. That would defeat the object of compressing it.
 
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Hi Richard,
i mistakenly said that i was using original plugs i have been usuing the spare ones which are identicle!
it still wont turn over with one plug.I have been using OBs for a long time,so i think my starting technique is ok.
Apart from stuck reeds which Vics says no to,i cant think of anything else.Thanks for all your precious time.Ronnie.
 
Is the plug coming out oily?
Is anything spraying out of the plug holes when turned over fast with no plugs?
I had a little strimmer motor that was so flooded it was hard to turn over.

40HP is not trivial to pull-start. You may just need to pull harder.
But check there is not some mechanism on the pull start intended to prevent starting in gear, which is accidentally engaging?
Can you turn it over slowly with a spanner on the flywheel?
 
bigman1 said:
If a "no start in gear" was in action surely it would be locked with the plugs out,plugs out spins great!
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That's correct Ronnie. It can't be the gear lockout.

I agree with everything that Vic and Steve have said. It's very strange.

Try unscrewing the plugs until they are loose and wobbly in their threads but not falling out. This will relieve the maximum compression and ensure that there is nothing mechanical going on here. Then try turning it over slowly using the cord. If you're able to turn it over TDC then make sure the HT caps are on firmly and the choke engaged and give it a firm pull. It should start even with the lowered compression but don't let it run for more than a few seconds.

Then start to progressively screw in the plugs and try again.

Richard
 
bigman1 said:
If a "no start in gear" was in action surely it would be locked with the plugs out,plugs out spins great!
Click to expand...

You'd think so, but there are 3 and a half possibilities I can see:
1) the plugs are too long and the pistons physically hit them
2) there is oil/water/fuel in the cylinders which won't compress
3) you just are not pulling hard enough! each cylinder is about 400cc? It's not a ladies' model.
3.5) something weird like you pull harder on the string something bends/moves and jams the mechanism.

Don't rule out no2 in a hurry. If the motor was laid up with oil in the cylinders, or a lot of turning over has gone on, or the oil injection is faulty, a lot of oil can be in the cylinders. It doesn't take all that much to bump the compression up.
I have a Yam 40 with pull start. It takes some pulling, but it feels like it turns very reluctantly rather than pulling up against a rigid stop. You can feel it's not jammed solid.
Luckily mine also has electric start.
 
Think I'd spray some penetration oil into the cylinders and leave it an hour or so, the rings may be stuck and scrapping the cylinder making it hard to turn over with plugs in.
 
I would be worried about the comments made about the demo....saying there was no smoke on start up...it's a 2 stroke...
Just a thought. Personally I worry if there isn't smoke on start up with any 2 stroke
 
lw395 said:
You'd think so, but there are 3 and a half possibilities I can see:
1) the plugs are too long and the pistons physically hit them
2) there is oil/water/fuel in the cylinders which won't compress
3) you just are not pulling hard enough! each cylinder is about 400cc? It's not a ladies' model.
3.5) something weird like you pull harder on the string something bends/moves and jams the mechanism.

Don't rule out no2 in a hurry. If the motor was laid up with oil in the cylinders, or a lot of turning over has gone on, or the oil injection is faulty, a lot of oil can be in the cylinders. It doesn't take all that much to bump the compression up.
I have a Yam 40 with pull start. It takes some pulling, but it feels like it turns very reluctantly rather than pulling up against a rigid stop. You can feel it's not jammed solid.
Luckily mine also has electric start.
Click to expand...

A compression test might give some clue as to what is going on. Exceptionally high readings would support the idea of there being a lot of oil in the cylinders
 
I meant excessive smoke,everything said so far i have done like extending the plugs,i did extend the plugs to the last 2 threads still massive compresion.I have come to the conclusion that the exhaust port might be blocked but what is the chance of that in 2 cylinders? Anyway i will put a scope camera down to check them,does anyone know how far down the ports are? Oh what a bloody nightmare! Thanks all again.Ronnie.
 
I don't think the exhaust ports can be blocked .... but even if they were it wouldn't stop you turning the engine over TDC unless some kind of huge continuous pressure was building up with no route out. However, I don't see how that is possible as you'd hear and feel it when you removed the plugs and, if there was a residual high pressure in the combustion space, no air would be drawn in on the intake stroke.

What happens if you ask someone to turn the engine over whilst sticking a finger over both the plug holes? Can you feel the pressure building until your finger is eventually pushed off the hole as the air rushes out?

Or even see if you can push a cork/s into the plug hole/s and see if you can blast that out.

Richard
 
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