See full version: 1979 Johnson 70 HP Sea Horse
Iam a big fan of these motors have a collection from 1970 to 1984 if yours is used in salt water , watch out for the salt build ,as they are well known to get water in to the ports i have done some improvement & modifications to these motors .
http://forums.iboats.com/showthread.php?t=528873
MAintenance - do a decarb - poke around on iboats for specifics.
Re: 1979 Johnson 70 HP Sea Horse [links]
Locate the lower gear case oil plug and remove it with a socket or screwdriver. Let the gear oil drain into a pan. Remove the gear case filler plug. Insert the hose of a hand pump oil bottle into the drain plug and pump in gear oil until it seeps from the top filler plug. Replace the filler plug and tighten it with a socket or screwdriver. Quickly remove the pump bottle hose and replace the gear oil drain plug. Tighten it with a socket or screwdriver.
Place the positive lead of a multimeter on the positive terminal of the battery and the multimeter negative lead on the negative battery terminal. It should read at least 12 volts, preferably 12.5 volts. Add distilled water to any low cell, up to the case neck. Charge the battery to its maximum standing volts. more
Use a hydrometer or multimeter to check the charge of your auxiliary battery, if so equipped. Remove the plastic cell caps from the battery top and dip a hydrometer into one cell at a time. The hydrometer floats should read in the green for all cells. Yellow or red floats indicate a battery discharge or weak cell.
Boat owners should routinely inspect and perform service maintenance on their Johnson outboard motors at frequent intervals. Doing so insures proper start-up and hours of pleasurable boating. Heat, friction and chemical pollutants in water can quickly compromise fuel and electrical systems. Since outboard motors have to work so hard all the time under constant torque, regular maintenance becomes all the more important in insuring smooth running and proper performance.
Trailer the boat to a convenient work location, and stabilize the trailer against movement. Place the outboard motor in the full tilt down position. Inspect the propeller for nicks, cracks and bent blade tips. Pull the prop shaft back and forth and from side to side. Any excessive movement indicates wear or gap in the propeller shaft thrust bearing. Remove all debris from the propeller shaft, including wound fishing line or kelp. Cut the line or kelp away with wire cutters.
Hook up a flush device and garden hose to the lower unit fresh water intake ports. Use a piece of wire to probe the water intake ports on both sides of the lower unit, as well as the upper exhaust port. Clean all debris away from the intake and exhaust ports. Turn the hose on, and start the engine. Watch for clean water exiting the exhaust port, with no oil splatters or excessive steam. Flush the engine for at least 10 minutes to remove salt water and algae. Disconnect the flush device.
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Motor Bearings : The center and lower crankshaft bearings are cast in bronze bushings (no rollers) and the connecting rod bearings are simply a bored and reamed hole in the aluminum connecting rod, very similar to the Briggs & Stratton lawnmower bearings. The top main bearing is a caged needle roller bearing with 27 needles. more
If you replace the points and still have running problems, you may well could have contaminated the point surfaces with oily fingers. If this may be the case, remove the flywheel, rotate the crankshaft until one of the points are open, wash it off with lacquer thinner, rotate and do the other set. Then insert a section of brown paper shopping bag in the points, rotate the crankshaft until the points close then pull this paper thru the points. This should clean them.
Magneto Ignition, Points & Condensers : If the ignition is magneto type, using points and condensers, the points were universal from the 1.5 hp up to 30 hp from 1952 to 1976 and then even to some 40 hp motors to 1973. Condensers pretty much followed this pattern from the 1.5 hp to the 35 hp at 1976 (excluding the 9.9/15 which are different).
This older ignition using condensers, if they start to break down, the motor can start and run for a while, but when things warm up, the condensers, and or coils can begin to short out internally which may cause the motor to die. You can crank until you are blue in the face but it refuses to start. Let it set for an hour, which lets these components to cool down and it MAY then restart. Time to change condensers, however hang onto the old ones as long as possible as the newer manufactured ones have a reputation of not being made that good.
A condenser is simply a lot of aluminum foil wrapped between waxed paper as an insulator. If the paper starts to deteriorate, after running for a while, the metal will heat up then expand. IF this happens in a location where the insulation is bad the metal shorts out to the next wrap, nullifying or shorting out so no output is achieved. But IF this is the case, many times when the condenser cools down, the short goes away until it warms up again. Once it has done this process a few times, then the short becomes rather permanent and the condenser can become inoperative