Grr - I hate small petrol engines! (Johnson 4hp 2-stroke)

VicS said:
OMC recommended that only Champion plugs should be used.

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That kind of thing is often more to do with who they get free parts from than what works best.
I find NGK are most resistant to failure by contamination.
 
VicS said:
QL86C are the correct plugs. They should be gapped at 0.030"

In idea from lakey's website for an improvised spark tester:

Sparktester.jpg



Its a modern CD ignition so no problems with points or condensers and coil unlikely to be any trouble ( old ones could deteriorate). Ignition module could be at fault. Hope not as thats £many to replace. Do a spark test . To check the system needs a meter with peak reading ( expensive Fluke) or a DVA adapter, ( It is possible to make a DVA adapter easily enough)

See http://issuu.com/cdielectronics/docs/practical_ouboard_ignition_troubles for CDI electronics troubleshooting guide.

I'd put a small wager on the bladder being holed!
but do you also have a remote tank and facility to connect it?
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With that spark tester, I would add a firmly wired ground between the handle and the business end.
So that if the current decides not to go where you first intended, you are not its second choice.
Better still, bolt the thing to the engine and stand back.
 
Another ignition test method when things get obscure, is it possible to turn this engine by means of a power drill driving the flywheel nut?
You can then at least roughly strobe the timing.
A broken CDI sensor can fire every rev, but not in the right place.

You can also ensure that petrol is moving through the cylinder, along with plenty of air.

Also, check there is nothing missing which might give an air leak downstream of the carb.

Also, old favourite, is there a kill switch?

Are there any Yamahas on Ebay?
 
I had a 4hp 2stroke mariner with similar problems,checked everything,eventually took it too a so called service dealer who thought it was going to be an easy fix.After six months and losing a seasons use of the boat and still hadn't found the fault I wrote to EP Barrus in desperation .EP Barrus sent the dealer a replacement coil which fixed it.When you looked at the old coil you could see where moisture had crept in and it was breaking down in use.
The engine was only about 2 years old.
 
lw395 said:
With that spark tester, I would add a firmly wired ground between the handle and the business end.
So that if the current decides not to go where you first intended, you are not its second choice.
Better still, bolt the thing to the engine and stand back.
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It's not dangerous as it's extremely low current. In the old days I often used to stick my fingers over the plug lead to see if I got a jolt. If all was OK I did!

Richard
 
RichardS said:
It's not dangerous as it's extremely low current. In the old days I often used to stick my fingers over the plug lead to see if I got a jolt. If all was OK I did!

Richard
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Not recommended!
1) CDI can have a lot more energy in the spark.
2) sending your muscles into spasm can have unforeseen consequences, particular near anything moving or sharp.
The current is sometimes much higher than people think, just the duration is very short.
 
I feel your pain. Our one was similarly temperamental. After tinkering for hours with carb could never really get it working right. Ended up 'riding' the choke a few times in order to get back to the mother ship... ;-)

We completely cured the problem by buying a used Mariner 4 stroke... although this cure was temporarily scuppered when my friend stored it lying down on the wrong side - big mess and wasn't the same for a long time.
 
Just had another run in the dustbin. One unexpected stop in maybe ten minutes' running, at varied throttle openings (but not up to full speed for long as I start to worry that the whole thing's about to break loose and thrash itself to bits on the patio among the remains of the plastic bin :) ). When it stopped, I took one of the plugs out and tried it against the block while pulling the cord; it produced convincing looking sparks although again I'm not an expert on what to expect. I didn't have Lakey's plank device to hand, although I've ordered a spark tester from Amazon which I assume does a similar job with less risk of zapping myself :)

So we're no further on with figuring it out :(

Pete
 
prv said:
To be clear, as a new coil sounds expensive, this was a problem of dying when throttled back from full speed to slow, and then failing to restart?

Pete
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It was the coil under the flywheel that had water ingress, probably when the engine took a dunking in a following wave.Engine was cutting out and then wouldn't start.
 
Lw395 mentions crankcase seals! So we are 2 stroke?no matter either way, there can be a lump of jelly in the tank.Suggest drain tank, then unscrew fuel tap. Flush out tank.check if small filter has moving jelly mass inside this filter.
Check inlet filter for presence of large wasp or queen bee?
Make sure all fuel is new.Some engines now have reed inlet valves in the crankcase. Never seen them, have you?
Just ideas, other things already covered like coils capAcitors, and ign modules.
 
Sounds like a coil problem to me, they can be very unpredictable. Could be a dodgy cut out switch, but if you're getting sparks then that rules that out. If you're getting sparks and it won't start, then either it's a fuel problem (if you haven't blown your carb out with compressed air line, then it could still be your carb. Don't ask how I know this!), or the sparks are not happening at the right time which indicates a coil problem. This can happen to a faulty coil when it gets warmed up - when the heat gets to the coil it expands and does all sorts of weirdness.

You could try checking the HT lead hasn't corroded away. This can still give you a spark, but not a very good one. When checking for a spark - you should get one with every stroke of the engine - you should have to pull it fast to get a spark.
 
Well Pete, you're getting all the right vibes on here! All from people who have almost lost their hair trying to revive outboards and lawnmowers!
 
mawm said:
If that is the case, it was a very small bladder.

It looked very much like #11 in the link below.

48280.gif
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Thats the hinge pin for the float arm


The bladder is #32 in the diagram below .... more like a little rubber teat

53210.gif
 
#32 - that's the bit! Sorry, bladder means something like a urinary or gall bladder to me. It had a small crack in it that was only visible when twisted at a certain angle. Replacing it cured the disease.

(The #11 when magnified in the parts list below looks something like the bladder)
 
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