mercury 50 blueband no power on cyl 3 and 4

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pinkmink

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Mar 9, 2010
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Engine will idle well but when I throttle up it stutters before reving up. If I pull the spark plugs off cyls 3 & 4 the engine idles and throttles up well, but if I do the same on 1 & 2 it idles but dies when I throttle up. I don't think it's fuel starvation cos it runs well on all 4 cylinders on WOT. I'm thinking along the lines of a broken trigger assembly but I have done the resistance tests and it seem ok. I have also swapped around the switch box and coils which makes no difference. Please can anybody shed any light on this.
 
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crem1

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Re: mercury 50 blueband no power on cyl 3 and 4

If the fuel pump is OK and you are gas at the carburator, then it's either carburator cleaning and/or idle screw adjustment or valves on reeds needs checking
 
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pinkmink

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Re: mercury 50 blueband no power on cyl 3 and 4

when I replaced the oil seals I looked at the reeds and they looked ok (but I don't really know what I'm looking for), wouldn't a reed problem affect the idle aswell. What kind of thing could be wrong with them? I'm pretty sure its not the pump, but I'm going to swap the carbs over to rule them out.
 
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crem1

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Re: mercury 50 blueband no power on cyl 3 and 4

It's the opening(distance between base of reed and the top position of the valve)
 
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verado7

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Apr 28, 2009
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Re: mercury 50 blueband no power on cyl 3 and 4

50 blue band is the older cousin to my classic fifty - no spark on lower 2 cylinders is classic switchbox fault - thats how mine failed a couple years back many others the same way .. you can rule out the stator very simply here by switching the position of the red/red-wht and blue/blue-wht. wires on the switchbox -so on the box you will put the red wire in place of the blue wire and so on -then fire it up and see if the problem moves to upper cylinders - if it stays dead on cyl. 3 and 4 - change the switchbox . this will tell you that both the high speed and low speed windings are producing power and omit the stator as source -
 
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pinkmink

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Re: mercury 50 blueband no power on cyl 3 and 4

Thanks you all your comments, I did alot of testing yesterday and decided it was very likely to be the lower carb idle as crem1 suggested, I have already cleaned the carbs but obviously not well enough. Today I swapped the carbs over and hey presto the fault has moved to 1 and 2, joy of joys. Somehow I need to get into the idle jet to clean it. They are the tillotson carbs with the blue cap on the fuel pump, anyone got any ideas how to clean the idle jet??
 
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pinkmink

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Re: mercury 50 blueband no power on cyl 3 and 4

So here is an update for anyone having similar problems. I decided to remove the idle capillary tube/jet to clean it even though the manual I have says don't do it (why not I do not know). It is the brass screw that has red screw lock on it. When I withdraw the tube I found what looked like clear fibres fouling the tiny fuel exit holes which I can only assume got sucked in though the ecomomizer hole adjacent to the mixture screw. Anyway this completely cured this problem that had been there even since I had the engine.

I hope all this will be useful to someone as it's taken me oven 6 months to sort this out.
 
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