Starting a 1965 Merc 3.9 with the top cowl off

dafaddah

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May 22, 2015
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Has anyone devised a method for starting an old Merc 3.9 with the cowl off?
I need to work on tuning the carb slow speed jet. I tried using a piece of rope with a knot in it but can only get one revolution of the flywheel before the rope slips off the teeth on top of it.
 

emckelvy

Commander
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Jan 16, 2004
Messages
2,506
I recall someone just talking about this! Try checking each tooth on the flywheel, you might find that one of them is notched for the starter rope.

Failing that, the little popper would probably fire right up with a hi-powered 3/8" or 1/2" drill adapted with a socket for the crankshaft nut (isn't it a 5/8" nut??).

One thing you've got to be really careful of, is the motor starting and the rope not releasing from the flywheel! Many moons ago I got a nasty welt on my arm from starting up an old Mark something or other, the starter rope handle was whipping around like mad. Man, did it hurt!

Last thought, and what Merc did to later models of this motor, is to drill a hole in the cover such that you can get a long, skinny screwdriver thru to the idle mix screw. Then you don't have to take the cover off at all! The hard part is making sure the hole is right in front of the idle screw. Measure twice, drill once! ;)

HTH........ed
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,031
Your local small engine shop may have a " universal " starter sheave that you can install temporarily for a rope.
 

dafaddah

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May 22, 2015
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Thanks to both emckelvy and racerone for your suggestions. None of my drills are strong enough to turn over the motor past the compression (even though that's not a good as I'd like it to be). I'd already tried that approach.
I looked at how I'd figure out just where to drill a hole for the slow speed jet adjustment but I just can't figure out where with enough confidence to put a drill bit to the cowl.
The starter sheave idea sent me looking for something that might work. I couldn't find anything but I think I might be able to rig something out of a pulley resting on the top of the crank with holes matching the threaded holes for the wheel puller. I'm going to follow up on that concept to see if I can't make it work. One thought would be to have a 5/8 socket welded to a pulley to center it and then drill through its web to hold it down to the fly wheel. The length of the socket would be what keeps the pulley above the flywheel teeth.
Another approach would be to rest a pulley on the teeth and bolt it down to the flywheel
All I'd have to do is to grind a notch in the pulley's edge to engage the end of a puller rope.
I'm going to get started on that approach in the next day or two.
I'll let you know how it turns out.
 

iggyw1

Master Chief Petty Officer
Joined
Oct 24, 2011
Messages
880
Thanks to both emckelvy and racerone for your suggestions. None of my drills are strong enough to turn over the motor past the compression (even though that's not a good as I'd like it to be). I'd already tried that approach.
I looked at how I'd figure out just where to drill a hole for the slow speed jet adjustment but I just can't figure out where with enough confidence to put a drill bit to the cowl.
The starter sheave idea sent me looking for something that might work. I couldn't find anything but I think I might be able to rig something out of a pulley resting on the top of the crank with holes matching the threaded holes for the wheel puller. I'm going to follow up on that concept to see if I can't make it work. One thought would be to have a 5/8 socket welded to a pulley to center it and then drill through its web to hold it down to the fly wheel. The length of the socket would be what keeps the pulley above the flywheel teeth.
Another approach would be to rest a pulley on the teeth and bolt it down to the flywheel
All I'd have to do is to grind a notch in the pulley's edge to engage the end of a puller rope.
I'm going to get started on that approach in the next day or two.
I'll let you know how it turns out.

Hi,

I am the one that emckelvy was referring to that was just talking about this same problem with my 1968 Mercury "39". I am trying to figure out a way to test and see if I have a spark or not at the plug with the cover off and I would like to check my compression too. I wrote about this not that long ago on this site and that's the question that emckelvy is probably remembering.

If you happen to come up with a solution to this problem, would you PLEASE post the answer to the problem here so I can learn how to do it too? Thanks in advance.
 
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