1964 Johnson Outboard 40hp not running at high speed

johnlazelle

Seaman Apprentice
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Apr 20, 2014
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30
Hi all,
The engine runs pretty decent at low speed, but when i throttle up, it dies. Any suggestions? Should the fuel "bowl" always be full of fuel"????
Thanks,
John
 

Robert Ellis

Petty Officer 3rd Class
Joined
Oct 17, 2011
Messages
82
I'm assuming you checked the fuel filter and that it is clean as a whistle. Have you tried manually pumping the bulb when you throttle up? If not, try it. If pumping the bulb keeps it going, it's quit likely you need a new fuel pump (or a rebuild).
 

johnlazelle

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Apr 20, 2014
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I did find a kink in the fuel line going from the fuel filter bowl to the pump, fixed that and now the bowl fills with fuel. Tried starting the engine at home and couldn't get it to start, no spark! Took the flywheel off and the key was sheared off so! I'm hoping it sheared because of it's age????
 

HighTrim

Supreme Mariner
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Jun 21, 2007
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10,486
No usually due to improper torque, or dirty tapers. Tapers must be clean and dry. Flywheel MUST be torqued to spec, 105 ft/lbs
 

johnlazelle

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Apr 20, 2014
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Thanks. I don't think the flywheel nut was Torqued correctly, it came off pretty easy!
 

Robert Ellis

Petty Officer 3rd Class
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Oct 17, 2011
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82
Thinking of the new key ... it should be aligned parallel to the crankshaft not to the taper and ... if it has a single 'punch' mark in it ... the mark goes down.

Since you have the flywheel off, great opportunity to do the ignition system. The Sierra points/condensers set is only $20. Do you know how to test the coils with an ohmmeter (new ones are a little pricey so I wouldn't replace them unless they're weak)? How do the wires look going to the plugs - easy and cheap to replace with new connectors and boots. You won't believe the difference in the resulting spark you get.

That's a great motor you have - I been running a 63 very regularly for quite a few years now and I love it.
 

Robert Ellis

Petty Officer 3rd Class
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Oct 17, 2011
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82
I meant to mention that valve grinding compound does a great job of cleaning up both the crankshaft taper and the corresponding inner face of the flywheel (hopefully the broken key didn't gouge either too badly). I found out the hard way that all traces of penetrating oil etc. must be removed from these 2 surfaces! Also, be sure to install the ratchet ring thingy on the flywheel before torqueing that big nut down. That hole in the middle of the ratchet does not quite fit over the nut - ask me how I know lol.
 

johnlazelle

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Apr 20, 2014
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30
Thanks. I have done the ignition system. Took it out again yesterday and It ran better but not perfect, still not running smooth at high speed. I'm going to get a new gas can and clean the filter and carb again because i did see some "floatable material" in the bowl. I'm pretty sure my problem is fuel related.
 

johnlazelle

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Apr 20, 2014
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Ok all, so here is what i have done. I have taken the carb off and cleaned and checked everything again, all looks good. Took flywheel off and checked all wires, adjusted points to .020, they were about .022. Took it out on the lake and i still can't get it to speed up. I know the boat should do about 20-25 mph and it just bogs down when you give it full throttle and wont go over 10-15 mph. While on the lake i decided to change the fuel filter. Unplugged the gas line to run the gas out of the line so i didn't make a mess. Replaced the fuel filter (again) and plugged gas line back in. Pumped the bulb a couple to time to make sure the filter bowl wasn't leaking, then fired her up. For a couple of minutes it went about 20 mph, then lost it and it bogged down again. I was thinking i wasn't getting enough fuel, now i am wondering if i am getting too much? Is there a secret to adjusting the new carb float? I also am using 5/16" fuel line which i am going to replace with 1/4", could that be part of my problem? While it is running at full speed, i tried choking the carb and it would run for a bit then start to sputter, so i put it back to auto mode. It seems to run about the same in auto and off choke modes. Really getting frustrated!!!! Any help or suggestions would be greatly appreciated!
 

Tim Frank

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Jul 29, 2008
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5,333
Did you remove, inspect, and clean the high speed jet? (orifice plug)
Is this motor new to you and if so, has it ever run properly?
 

johnlazelle

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Apr 20, 2014
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Yes I checked the high speed jet and it was clean. The motor has not run for about 15 years, but I know the owner and it ran fine and had a lot of get up and go.
 

johnlazelle

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Apr 20, 2014
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30
Yes i did, i completely removed it and cleaned it, even though it was already clean.
 

freddybell79

Cadet
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Sep 3, 2014
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10
I am having the same problem on a 1965 40hp big twin. should I try the carb rebuild or may it be another problem?
 
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