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johnson 70hp 1978

C

caterman

New member
hi
engine was running fine when i went to buy the boat, now won't start. plugs get very wet and when i crank over with plugs out it spews out petrol from the plug holes...........help please:( ok got engine running again woooo hoooo but......tick over quite high and no water coming out the back...is it supposed to exit from the 2 holes at the top of the leg
 
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Try putting the lower unit in a barrel or similar, water level ABOVE pump.
If still no water, down with gearcase and change impeller.
(Take out screw through shift rod under the carbs, port side, before dropping the unit.
Take a look at the thermostat at the same time.
 
thank you, all seems well now, found out won't spurt water till thermostat opens at 143 degrees........where is the thermostat and can you test like a car one? thanks for advice
 
Thermostat is under that plate attached to the top portion of the cylinder head. Yes, you can test it. Thermostat water outlet is the holes/slots just above and to the rear of the cavitation plate.

(Exhaust Relief Ports - Exhaust Housing (Inner/Outer)
(J Reeves)

The long housing between the powerhead and the lower unit is called the exhaust housing. There is a inner housing within it that has a heavy duty seal around the bottom of it, or heavy duty seals around a inner extension between the housing and the lower unit.
The red hot exhaust travels down thru that inner tube and out the propeller with a somewhat supply of water to cool the propeller hub. A good amount of water surrounds and fills the space between the outer and inner tube, otherwise the outer housing would get so hot that the paint would burn off.
Some water pumps, for some reason (differing even when new) exert a great amount of water pressure, and if the exhaust housing seals are in perfect condition, the water fills the tube to a point of overflowing.

This brings into play those two holes or slots, whichever the engine might have, at the top rear portion of the exhaust housing just below the powerhead.

Now, if those two holes/slots weren't there, water would continue to flow up into the cylinders. Water not flowing out of those holes is no concern for alarm UNLESS that outer housing suddenly becomes extremely hot..... the warning horn should sound long before that happens.
The main reason for those holes being there (exhaust relief holes) is that when at an idle, there is an extreme amount of resistance encountered by the exhaust trying to escape due the fact that the outlet via the propeller is now blocked by a wall of water. The escape route in this case is for the exhaust to escape out those two holes, otherwise the engine would slow down quite quickly and die. If exhaust cannot escape, air/fuel cannot gain entrance to the engine.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
 
thank you for your help and advise, all seems good now except having trouble starting it from cold, once started will keep starting no problem but leave it a few hours a no chance seems like luck if it fires
 
These motors need to turn over quickly.------------If they turn over slowly the ignition system will not fire.----------------So check the starter and make sure you have a topnotch battery.
 
Starting procedure:

Pump fuel primer bulb up hard.
Apply some throttle in neutral to take engine off the idle setting (Open throttle butterflies somewhat).
Crank engine and engage electric choke until engine fires and starts.
Release key to the ON position..... engage choke as needed until engine warms up.

Is this your starting procedure? If not, it should be.
 
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