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4 HP Mercury

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mr.mws

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Have a 4hp Mercury (Serial No. 2773693)that has no spark. I am curious as to what model year this is. What should be tested first? How can I be sure what to replace? Is there a way to test a coil? Any thoughts are appreciated.
Mike
 
Hello Mike, to start with that is a 1970, Model 40 (4 hp).

It has a Thunderbolt II "Phase Maker" ignition system.

There are 3 main components to your ignition system.

The stator, which is one unit but modular, is made up of low speed coils, high speed coils and a capacitor.

The points - in this case they "close" to pass on the power stored in the capacitor and, the ignition coil.

If the stator is toast you might have some difficulty in finding another one - been discontinued a long time and sold for well over 400 bucks when they were available.

The points are still stocked (about 100 bucks) and the ignition coil is also stocked (about 70 bucks) by Merc.

Testing -

Remove the Green and the White wires from the coil (that feeds the sparkplug) and simply do an ohm test accross the two posts - should have basically NO resistance there (.3 - .35 ohms)

If the coil is ok (and you still have the wires off) you can check the points next. Ohm's again - one lead to the White wire the other to any good ground point on the engine block - then SLOWLY rotate the flywheel by hand - you should get the needle sweeping between No continuity and full continuity (as the points open/close).

No "swinging" needle = toasted points.

Last test will tell you if the stator is shot. With the wires still unhooked from the coil, set your ohm meter to X1000 and put the positive lead on the green wire and the negative on a ground spot - you should get NO continuity.

Reverse the leads (so negative on the green wire now and positive on the block) and you should see 20-50 ohms resistance.

One final thought. This model/vintage is (maybe) worth about $200 in the used market if it's running. I would keep that in mind when trying to determine how much you want to spend to get her running...
 
I would take these motors all day for $200,not sure where you live but you wont get them in running

galamb said:
Hello Mike, to start with that is a 1970, Model 40 (4 hp).

It has a Thunderbolt II "Phase Maker" ignition system.

There are 3 main components to your ignition system.

The stator, which is one unit but modular, is made up of low speed coils, high speed coils and a capacitor.

The points - in this case they "close" to pass on the power stored in the capacitor and, the ignition coil.

If the stator is toast you might have some difficulty in finding another one - been discontinued a long time and sold for well over 400 bucks when they were available.

The points are still stocked (about 100 bucks) and the ignition coil is also stocked (about 70 bucks) by Merc.

Testing -

Remove the Green and the White wires from the coil (that feeds the sparkplug) and simply do an ohm test accross the two posts - should have basically NO resistance there (.3 - .35 ohms)

If the coil is ok (and you still have the wires off) you can check the points next. Ohm's again - one lead to the White wire the other to any good ground point on the engine block - then SLOWLY rotate the flywheel by hand - you should get the needle sweeping between No continuity and full continuity (as the points open/close).

No "swinging" needle = toasted points.

Last test will tell you if the stator is shot. With the wires still unhooked from the coil, set your ohm meter to X1000 and put the positive lead on the green wire and the negative on a ground spot - you should get NO continuity.

Reverse the leads (so negative on the green wire now and positive on the block) and you should see 20-50 ohms resistance.

One final thought. This model/vintage is (maybe) worth about $200 in the used market if it's running. I would keep that in mind when trying to determine how much you want to spend to get her running...
Click to expand...
 
I wish i could get my hands on some running vintage 4 hp mercury outboards for $200 running,When rebuilt properly they are as good or better then the new ones!
 
If you have trouble getting a stator you cal allways just convert it to the phelon points style ignition if you can find the parts? You need the flywheel, points plate and cam and is plug and play. look for ignition parts for the model 3.9 in the late 60s.
 
Thats not my message Jeff,All i said was i wish i could get a few Mercury 4 hp motors for $200 id take them all day.The message above that is someone elses?The thread got mixed up some how?
 
It may take a few cheap ones to get one good gearbox. If you cannot remove the prop chances are the gearbox cannot be resealed. It is the gearbox that normally condemns the motor. Ignition parts can be found if you want to sell your firstborn child.
 
If its a running motor you don't need ignition parts/I only have two and the gear boxes(if you mean the lower unit gears) were not an issue.
 
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