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Old 23 February 2015, 02:52   #11
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Thanks All,

It doesn't have one of those levers.
It is approx 1991.
I have a workshop manual but can't find the flippin' thing!

I'll run another compression test and report back.

I swapped the carb for an identical one yesterday and its response to squeezing the primer bulb was different. I think I have found a leak in the fuel line.

The fuel pilot jet seems OK in that I can blow through it with the necessary other ports blocked.

With the new carb the symptoms were the same. Interestingly, the mixture needle had to travel a long way in either direction to affect the running. If for no other reason than to satisfy myself I might check the timing anyway.

Call me a wimp but investigations had to stop when it started to tip down with rain yesterday.

Thanks for the inputs.

Watch this space.
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Old 23 February 2015, 03:17   #12
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Upper cylinder lubricant is for four stroke engines. Please look at the note towards the bottom of the specs.

If you try to use the fuel that's in the tank, you also are inspecting the quality of the fuel. I squirted some fuel down the carb once and it was that which caused me to discover the operator has filled his tank with diesel and mixed with two stroke.Click image for larger version

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Old 23 February 2015, 15:39   #13
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Quote:
Originally Posted by RIB-Teccie View Post
Upper cylinder lubricant is for four stroke engines. Please look at the note towards the bottom of the specs.
Upper cylinder lubricant is just that, upper cylinder lube which is exactly what 2 stroke Yamaha's fitted with Autolube get, with or without fuel.

I guess I got the good stuff As you can see my can is probably 10+ years old since I use is sparingly.


Propane works great too.

Quote:
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If you try to use the fuel that's in the tank, you also are inspecting the quality of the fuel. I squirted some fuel down the carb once and it was that which caused me to discover the operator has filled his tank with diesel and mixed with two stroke.Attachment 103075
I have seen diesel put into older gasoline vehicles, and gas put into diesel vehicles, which is all too common. We had one company we serviced where it happened to the same truck twice in one month, even though it was labeled in BIG lettering, DIESEL ONLY in block lettering above the fill cap.

You are 100% correct that bad fuel is often the cause of issues, and unless checked thoroughly can waste a lot of time being diagnosed. The nose is always a good first check.
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Old 23 February 2015, 16:03   #14
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I really can't be bothered to debate this one.

1) pulling choke in and out - bad advice

2) showing the incorrect outboard - bad advice

3) Recommending easy start and not naming a suitable brand (if one exists) - bad advice

4) Upper cylinder lubricant is for the top of a vertical cylinder engine. It (as the name suggests) lubricates the upper part of the cylinder of an upright engine, usually one which is older.

5) The yamaha autolube system is not an upper cylinder lubrication method. It injects just forward of the carb and mixes with the fuel as it hits the reed valves. It is drawn through the intake port as an air oxygen mix and is detonated on the compression stroke. It lubricates the rear of the Pistons and bearings as it comes through the reeds. It has nothing to do with upper cylinder lubricant in the traditional sense. On a Yamaha outboard or any two stroke outboard the majority of the lubricant comes from the rear of the Pistons and cylinders. Any unburnt oil will have some lubricating capabilities but when you remove the head you will find a 4mm (ring) at the top of the cylinder which has missed out on lubrication (to a minor extent) over the life of the engine.
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Old 23 February 2015, 19:10   #15
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I really can't be bothered to debate this one.
Then lets try to help the guy get his outboard running

Is propane okay to use? I really try to discourage people from dumping raw gas down a carb. I have seen too many fires in my automotive career.
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Old 24 February 2015, 02:52   #16
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4) Upper cylinder lubricant is for the top of a vertical cylinder engine. It (as the name suggests) lubricates the upper part of the cylinder of an upright engine, usually one which is older.

5) The yamaha autolube system is not an upper cylinder lubrication method. It injects just forward of the carb and mixes with the fuel as it hits the reed valves. It is drawn through the intake port as an air oxygen mix and is detonated on the compression stroke. It lubricates the rear of the Pistons and bearings as it comes through the reeds. It has nothing to do with upper cylinder lubricant in the traditional sense. On a Yamaha outboard or any two stroke outboard the majority of the lubricant comes from the rear of the Pistons and cylinders. Any unburnt oil will have some lubricating capabilities but when you remove the head you will find a 4mm (ring) at the top of the cylinder which has missed out on lubrication (to a minor extent) over the life of the engine.[/QUOTE]

he,s right you know the 2 stroke oil does most of its lubricating whilst being compressed in the crankcase before going through transfer ports into the upper cylinder.(I don't remember much from collage )
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Old 24 February 2015, 05:19   #17
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I am assuming the engine has been run on 1:100? On 1:50 there is a chance the rings could be gummed in.
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Old 24 February 2015, 16:23   #18
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Quote:
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I am assuming the engine has been run on 1:100? On 1:50 there is a chance the rings could be gummed in.
It's got 1:50 in it at the moment as it has just had the cylinder walls tickled with a hone, new pistons and new rings. No autolube and judging by the crankshaft it never had one.

Cold compression tests (with a cold battery) showed 120 psi on both cylinders. (Nothing has had a chance to bed-in but the fact they are the same is reassuring).

Using a DIY manometer showed the TDC pointer to be on target and the timing mark aligned with that.

The check valve in the primer bulb is a bit suspect so I'll fit a new primer bulb and see what happens...

Flippin' thing.
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Old 24 February 2015, 16:47   #19
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Now we're getting somewhere.

1) why did the engine need a decoke or just stripped down?

2) At a guess, how many hours would be on it when it was stripped?

3) TDC may be fine, but we're the timing stops altered?

4) the yams are usually forgiving even if the rings are gummed in.

5) Try a squirt of fuel down the carb from cold and let me know how it fires.

6) You have good spark so it can only really be a fuel system or timing issue unless you went mad with the honing tool!
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Old 24 February 2015, 17:32   #20
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Thanks,

1) The thermostat got blocked with a bit of impeller and it slowed to a dignified halt. After cooling it restarted but then slowed to a halt again. The pistons were scuffed and there was a small amount of scoring on the cylinder wall (not enough to catch a fingernail or edge of a credit card)

2) Hours unknown.

3) The timing stops weren't altered. The timing mark on the ignition plate lines up with the timing pointer when at minimum throttle.

4) Let's hope so...

5) Will do.

6) The honing was pretty light and I am confident in the chap who did it: he wears a brown shop-coat with biros and a vernier caliper in the top pocket plus 'Michael Foot' glasses - old skool Engineer (with a capital 'E').

The real killer is that this engine was bought to replace a Mariner version of the same engine that ground to a halt after picking up a carrier bag round the lower unit. That started first time, every time, for the twenty years we'd had it (ex MoD contract).

I'll squirt some fuel into the carb tomorrow and see what happens.

Many thanks

Hugh
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