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Old 01 July 2015, 18:51   #11
Country: UK - England
Make: Humber / Phantom
Length: 5m +
Engine: Lots of Yamahas
Join Date: Feb 2006
Posts: 114
If the spark is there there is no problem with the ignition system, there are no points and timing can't be out as you cannot adjust it on the 4hp, it has a fixed timing and ignition curve.

99% of the time it is the carb at fault. Go through it again. Check jets, low speed one screws into the side of carb easy to miss if you don't know it is there. Diaphragms definatly the right way round with the little cup washer and spring in position? Spring fits into recess in fuel pump casting and cup washer fits onto spring and presses against diaphragm.

Compression? Without a compression gauge you should be able to get a good feel for it pulling it over. At 30years old the crankseals may be starting to go which does affect starting.

Far better engine than anything four stroke on the market these days.

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Old 06 July 2015, 07:08   #12
Country: UK - England
Town: Sheffield
Boat name: Touch Bottom
Make: Avon
Length: 4m +
Engine: 50 hp Merc Power t&t
Join Date: Jul 2008
Posts: 232
Originally Posted by paintman View Post
If you squirt a small amount of petrol into the carb intake does it attempt to run?
Has it ever run properly in your ownership?
Squirty has done the trick, so it could have been the reed valves throwing the dummy out..

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