Merc 300

[Banoe]

Hi,
I was just given an old Mercury Merc 300 model outboard. It original color appears to be white it is painted about six colors of black. I checked the compression and it has about 105psi in all four cylinders. I don't think i have any spark but I dont have a set of controls to hook up to the engine so that may be the problem.

Questions........ What year motor is this Mercury?
What is the hp of this motor I am thinking 30hp?
Would I be able to get spark with the control harness hooked up?
Are there wires I can jump to get spark?

Thanks in advance, any help would be appreciated.

 

[carholme]

Re: Merc 300

Do you know the s/n of your engine?

Gerry

 

[Banoe]

Re: Merc 300

Do you know the s/n of your engine?

Gerry

1356498

 

[tomhath]

Re: Merc 300

I believe they were only made the 300 for a couple of years in the early 60's, maybe 1960 and 1961? It's 35hp.

 

[carholme]

Re: Merc 300

Can you double check the s/n?

Old Mercs lists the 300 as:

Merc 300

with a s/n range of 1271885 thru 1335464

Parts Listing:

MARK 35A MERC 300/350 - Mercury, Mercruiser, Force, etc. Parts Lookup

Gerry

 

[1960 Starflite]

Re: Merc 300

Same engine on my 1960 Glastron. 35hp. It has a magnito ignition which doesn't require external electrical power supply to run. You can either pull start it or jumper the starter with battery cables to crank it without the control electrical cable. To shut the engine off, you will need to ground the magnito. You will see a small gauge wire on the side of the mag, just touch a screwdriver across the stud to mag case.

No spark? The points are corroded and/or the condensor needs replaced. Four bolts and pull the mag off for service. No problem with timing, the mag will only go back on in one place, mag has a blind spline.

Be super careful, mag parts are hard to find and very costly.

 

[Chinewalker]

Re: Merc 300

Be super careful, mag parts are hard to find and very costly.

And brittle! They used kind of a Bakelite plastic on the body cap, rotor and distributor cap. Too much torque on a bolt, prying with a screwdriver, etc. will crack things you don't want cracked! If things come apart hard, just go slow and easy on it.

Quick tip - you can bench test the magneto once you get things cleaned up. Two steps. First, with the caps off, you can ground the housing against a bench vice, and hold the coil tang about 1/2-inch away from the vice. Spin the mag over and you should get a good spark jumping that gap. If it passes that test, then second, with the mag assembled, load four plugs into the plug caps, set them in the vice, hold the mag body against the vice and spin over. That'll tell you the cap, distributor and rotor are working... Saves you installing it on the motor and then discovering something is amiss.