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Old 22 May 2014, 06:38   #1
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Yamaha 55hp AE 663

Hi,having a mare with this engine,won't run on no1 cylinder until about 3500 rpm and then it still drops in and out,strong sparks both cylinders compression tested at 120psi on each cylinder,new cOils fitted tried swapping coils but no difference,ran engine with air box off and sprayed fuel into carb no difference anybody any ideas please.......?
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Old 22 May 2014, 07:33   #2
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Take out the reed block and have a look at the piston skirt.
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Old 22 May 2014, 11:15   #3
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Hi Davie, what exactly am I looking for?
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Old 22 May 2014, 12:23   #4
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The bottom of the piston. I had a problem with one which had that exact problem. Why it burst into life now and again remains a mystery.
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Old 22 May 2014, 12:33   #5
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How did you repair it,does the lower skirt break off ? Secondly is it a viable repair cost wise.
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Old 22 May 2014, 16:06   #6
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Checked piston skirt tonight all ok,,at a total loss now,I'm wondering if the spark it is producing is too weak and the plug is oiling up,or sparking at the wrong time.
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Old 23 May 2014, 15:34   #7
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These are the worlds easiest engines PM me.
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Old 23 May 2014, 15:44   #8
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Yes, your small jet on the top carb will be blocked. Jet is housed under the small brass screw. Do not attempt to remove this jet unless you absolutely have to, they can chew up and write the carb off.

Simply blast through with air or even coke.

The small jet Is the slow running one.

Another thing to look for is the wires that enter the stator plate below the flywheel, at that age they go hard and crack, so when you close the throttle they touch and when you open it they don't and the spark fails.
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Old 23 May 2014, 15:57   #9
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This is the jet.Click image for larger version

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Old 23 May 2014, 16:21   #10
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Hi Teccie, top jet cleaned all clean as a whistle,waiting on a CDI unit and stator ring.i changed a ignition coil but the replacement coil was from a 3 cyl 60hp which seemingly works at a different voltage.
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