Untraceable gremlin

Hi all.I am in need of some fresh ideas 'cos I,ve run out for the moment.about a month ago I decided it was time to go fishing so I hauled out the boat checked lower unit oil and used fresh gas.The motor is my 1973 40 hp norseman,hitherto as reliable as a rolex. It started up on the second push of the button and I then let it run at varying speeds up to a high idle in it's tub of water for about 30 mins. No problems at all so I switched it off then a few days later I took it down to the lake but it flatly refused to even cough.I brought it home and started running checks.!: removed carburetor and soaked in cleaner and cleaned off including slow speed holes,rebuilt and remounted.Removed flywheel ,cleaned and set points using Franks tool,now spot on,I have sparks the great god Zeus would be proud of.Checked compression,105 on each,more than I would normally expect on a motor this age.Still no good.I have removed and checked the carb at least 4 times since and now have very little hair left.If anyone has any ideas or suggestions I would greatly appreciate hearing them as I.m sure I must be missing something somewhere.

Does spark jump a gap of 5/16", yes or no ?----If you have gone over the carburetor 4 times I would say it is NOT a fuel problem.

racerone said:

Does spark jump a gap of 5/16", yes or no ?----If you have gone over the carburetor 4 times I would say it is NOT a fuel problem.

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Yes Racer the spark is good as I said,easily jumps a 1/2 inch gap.The motor actually fires up and runs for about 5 or 10 seconds then just dies.I'm beginning to wonder if there's something else going on like one of the seals but I
've never had that happen so I don't know what the signs are. I just put it back together for about the 6th time having done everything on the carb there is to do but I 'm stumped

A motor will run for more than a few seconds on fuel from the carburetor bowl.-----So the carburetor bowl is empty or the high speed jet might be plugged.----The high speed jet ( orifice plug ) is way inside the carburetor bowl.----What setting do you have on the low speed mixture needle ?------Checked the reed valves ?

That's exactly what I was thinking,the fuel does not seem yo be getting sucked out of the bowl.Yes I have removed the high speed jet and cleaned it thoroughly though it was clear.Low speed needle out 2 1/2 turns as it has been for last two years when running perfectly. Visually checked the reeds using a flash light and seemed ok. Maybe next step is remove manifold and make sure though in all the motors I have worked on(quite a few but not as many as you) I have only ever come across one reed problem.What do you think about the seals idea.

Nobody have any ideas?

What happens when.you pump the primer ball?

Sorry for delay. Nothing happens if I pump the bulb.The bowl is full and the bulb is hard.When I can get it to run I have to juggle with the throttle to keep up the revs so it won't die and keep them down to stop it running away.I have completely changed the carb and stripped and rebuilt the mag and everything there is spot on,plenty of fuel from the pump and sparks that are bordering on the dangerous.I have given up on it for a little while and am working on a replacement that I have had waiting for a couple of years and it looks as if it could be a really good motor.1960 RDS 40,from the looks of the inside of the gearcase it has not done many hours so I have high hopes.