Help! any two stroke outboard experts out there?

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9 years 7 months ago #33463 by mikethebike
Hi guys I have recently acquired a 1980s 80HP mercury. had it fully serviced and it ran great first turn of the key, took it out today and it was hard to start so assumed i had over squeezed the bulb thing and flooded it after a few Minuits tried again and it ran just fine, went out of Napier planing at about 35k
all good, got to fishin spot and at low revs it stopped, UMM bit disconcerting squeezed the bulb again a couple of times and a bit of choke and it started ok and motored to another spot again at low revs stalled but restarted after squeezing again, tried putting in reverse and again at low revs stalled, so lots of revs goes good low revs not so good but does tick over ok, Im thinking fuel supply issue what do you guys think I would like to get it sorted.
cheers mike.

Mike and Suzi living the lifestyle in sunny central hawkes bay, Still loads of animals oh and we still have our Zebra truck.

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9 years 7 months ago #444274 by spark

mikethebike;443939 wrote: so lots of revs goes good low revs not so good but does tick over ok, Im thinking fuel supply issue what do you guys think I would like to get it sorted.
cheers mike.

Assuming that your carby is tuned correctly (it may not be - if you can find the book for your outboard it should show you how to set the idle speed and mixture), you could have a vacuum leak (air getting into the intake system somewhere between the carby and the motor) - because this vacuum leak air doesn't have any petrol mixed in with it, it will cause the mixture to lean out and the engine to run rough at low rpm, but at high rpm, the air leak is too small to affect the mixture of the much larger fuel-air mass-flow through the induction system and so the engine will run ok. A vacuum leak could be caused by a stuffed gasket between the intake manifold and the engine, or the manifold and the carby. It could also be a perished vacuum hose, or even a hose that has come off of it's barb fitting. Your carby might even have a vacuum operated rubber diaphram that is perished and is letting air go where it shouldn't.

I think that if you had a fuel supply issue, the engine would likely run well at low rpm when the rate of fuel consumption is low, but run rough or stall at high rpm when the fuel system can't supply enough fuel to keep up with the demands of the motor.

Cheers

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9 years 7 months ago #444280 by mikethebike
Hey thanks sparky makes good sense, sadly dont have a manual it is 25 years old, but i can probably figure it out, whats the likelihood of partial blockage was thinking that the squeezing of the bulb was overcoming the fuel supply problem,
mike

Mike and Suzi living the lifestyle in sunny central hawkes bay, Still loads of animals oh and we still have our Zebra truck.

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9 years 7 months ago #444404 by spark

mikethebike;444146 wrote: Hey thanks sparky makes good sense, sadly dont have a manual it is 25 years old, but i can probably figure it out, whats the likelihood of partial blockage was thinking that the squeezing of the bulb was overcoming the fuel supply problem,
mike

Unlikely to be a partial blockage, because a partial blockage would result in an engine that runs well at low RPM (low fuel consumption rate) but plays up at high RPM (high fuel consumption rate - can't get enough fuel past the blockage to keep the engine happy).

When the engine is running rough at low RPM, does squeezing the bulb before it stalls make it run smoother?

If you then let is stall when running at low RPM, and you then squeeze the bulb, does the bulb feel "empty" like the fuel line is full of air, or does it feel "full" (of fuel)?
Is the resistance to the first squeeze the same as the subsequent squeezes (full of fuel), or is it very easy to squeeze to start with and then it gets harder (contains air)?

You might have a vacuum leak in the fuel line between the squeeze bulb and the outboard. At low RPM when the engine isn't sucking very hard on the fuel line, air could be getting into the fuel line faster than it is sucked out by the engine resulting in the fuel pump losing it's priming and the motor starved of fuel.

Cheers

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9 years 7 months ago #444408 by mikethebike
Ah ha yes the second, easy at first then gets hard and incidentally the fuel line dose not look great the rubber looks a bit suspect, i was thinking of changing it anyway so maybe do that first before pulling engine apart eh, will let you know how i get on planning on going fishin again on sunday!
Thanks mike.

Mike and Suzi living the lifestyle in sunny central hawkes bay, Still loads of animals oh and we still have our Zebra truck.

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9 years 7 months ago #444578 by mikethebike
Well sparky put a new fuel line on and out of the water it sounds better but last time it was only under load the problem occurred so next week end will give it a good try out and let u know how i get on.
Cheers mike.

Mike and Suzi living the lifestyle in sunny central hawkes bay, Still loads of animals oh and we still have our Zebra truck.

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