Unfindable(so far) gremlin

[Geoffrey Graydon]

Good morning all. I have a problem with my 73 40hp Norseman that so far I have not been able to cure.The problem is: she starts just fine and runs just fine,no spits misses or hiccups until about 3000-3500 RPM and just refuses to go above that.Correct revs are I think 4500 -5000 without looking in the book.I have been through just about everything I can think of.Compression105/110 spark 7/16 open air gap ,points timing spot on using Franks timing tool, fuel pump delivering just fine,carb stripped cleaned and rebuilt at least three times with careful attention to all the slow running galleries and the main jet.Throttle plate is opening fully,link and sinc fine. Could it be that this engine likes to run advanced by a few degrees? I would welcome any input from you guys who are more experienced tan me, thanks. I have been running this motor for several years now and I have not changed anything.

 

[F_R]

So this problem has existed for several years? You mean it never has performed well? What do you have on it for a prop? What kind of a boat?

 

[Geoffrey Graydon]

It was fine up until halfway through last year, still has same prop but I have tried with slightly smaller one as well.The boat is an elderly 15ft seaswirl. According to my GPS I used to get about 27 MPH but now lucky to get 8.

 

[F_R]

OK, I'm going to go out for a long pass on this one. Have you inspected the BOAT? It wouldn't be the first one to have 50 gallons of water under the floor.

And/or, how about the boat bottom? Any fouling from marine growth? You would be amazed at how much drag can result by just a few barnacles or whatever grows in your part of the world.

 

[flyingscott]

I will go out on a limb and say you have at least 1 bad condenser.

 

[Geoffrey Graydon]

OK, I'm going to go out for a long pass on this one. Have you inspected the BOAT? It wouldn't be the first one to have 50 gallons of water under the floor.

And/or, how about the boat bottom? Any fouling from marine growth? You would be amazed at how much drag can result by just a few barnacles or whatever grows in your part of the world.

The boat is bone dry inside and has no growth as it lives on the trailer most of the time

I will go out on a limb and say you have at least 1 bad condenser.

Ah,but condenser(capacitor) failure would surely lead to rough running and there's no sign of that,just lack of peak revs.

 

[F_R]

OK, I believe you, You do know what I'm talking about, right? Most old boats had sealed floors with air space below the floor for floatation. A guy would bring his nice clean boat in on the trailer and say it won't get out of it's own way. I would pull the drain plug out of the floatation chamber while stood there and he would gasp at how much water was in there. Often in the neighborhood of 500 pounds.

Maybe that is not the problem here, just a FWIW guess.

Ah, the Good Old Days, eh? Those old boats would float when swamped---but upside down with nothing to grab onto.

UMM....I am Frank. You asked about the timing. Maximum spark advance is fixed. If you used the timing fixture correctly, the timing is spot on.

 

[flyingscott]

The boat is bone dry inside and has no growth as it lives on the trailer most of the time

Ah,but condenser(capacitor) failure would surely lead to rough running and there's no sign of that,just lack of peak revs.

Would it?

 

[Geoffrey Graydon]

Would it?

I would think so though I have no proof.I have 17 or18 outboards in my shop that I have worked on and /or rebuilt and though I do not have the vast reservoir of experience that you guys can muster I am not a complete beginner.Having said that Scott I will try new capacitors but the only thing that has been suggested so far that is possible is bad gas.to be honest I'm not completely sure of it's age and it was stabilised.Regarding under the floor Frank,I have renewed it and there,s only room under it for a few pints and I drain it before I launch every time I guess a trip to the gas station is indicated.Thank you all,I will let you know the outcome.

 

[flyingscott]

Pretty sure that has a low tension magneto. They tend to destroy condensers

 

[Geoffrey Graydon]

It's the universal magneto common to just about all pre 74 Johnnyrudes below 40 hp since Noah was a junior seaman on the Ark

 

[racerone]

The universal magneto was used from about 1950 and up to about 1986 ( 4 HP ) ----It is a wonderfully simple and reliable unit.----2 ignition systems under the flywheel.---Allows motor to run on one cylinder in case of failure.----Cheaper to own and maintain then some electronic systems.----But only if you take the time to learn about this simple unit.

 

[flyingscott]

It's the universal magneto common to just about all pre 74 Johnnyrudes below 40 hp since Noah was a junior seaman on the Ark

Sorry off by a yr and am still going to go with a bad condenser.

 

[racerone]

Perhaps some do not know the difference between the 2 types of magnetos !

 

[flyingscott]

You two seem to have all the answers I will leave you to it then. Good luck with your motor.

 

[Geoffrey Graydon]

You two seem to have all the answers I will leave you to it then. Good luck with your motor.

I will replace the capacitors,Also the suspect fuel.