Need help on a Mercury outboard engine?

Question

I have a 1974 Mercury 110, 9.8 HP, that stalls intermittently. It just "shuts off" at any speed (randomly) and generally will resart with one pull of the starter. The in-line fuel bulb stays hard, I don't have to pump it to restart the engine. Seems to get somewhat worse the longer it's run. IMHO, it feels like an electrical cut-out (I'm an auto tech, understand engines, but not much experience with outboards) Has all new fuel lines and pump bulb, plugs, and new points?(dealer installed, thought it was CDI) Runs great otherwise, just randomly quits with no warning. Any help would be appreciated, TIA!!

The serial # is 3448025.

Answer 1

In 74 it was a maker point ign, I am thinking and will let you know on Monday, which ign for sure and give you some more info. There were 3 different ign back then. Do check the temp, it could be heat related, they usually ran less than 120 deg, no thermostat. Disconnect the stop switch, that is just a rubber cap over two contacts, they get water in them and will drive you nuts. Just un do the nut behind the switch and peel the cap off, dry and clean. Do you have the serial number of the motor to be sure of the ign and year.

Your motor is a 1972-73 with a Thunderbolt maker point ign. It has a low and high speed coil under the flywheel with two points and a condenser. Point gap is .020. You will be ohm testing the high and low speed coils, the low speed coil, test between the red and yellow leads, 320-400 ohms. the high speed coil blue and yellow 1600- 2000 ohms. If they test good, it is a good bet the condenser is going bad. The points only need cleaning and gaping, they fire when they make contact and don't give much problems. If you need more info let me know.

Answer 2

I had the exact same problem with a '74 15hp Evinrude. Ran great but would just shut off the longer it was used, and then would have to wait several minutes for it to start up again.

Have you checked the water pump? A lot of these older outboards will simply shut off when they get too hot. If the engine isn't getting cooled, the longer you run it the more frequently it will just shut down. Sounds like the water pump to me. Best thing to do is mount the motor over a barrel of water, crank it up, and check to see if you're getting water flow out of the drain tube. If you're not seeing a good full stream, it's the water pump.

From experience, those motors will go forever with a bit of TLC at the start of the boating season. Enjoy. Have fun. Hope this helped.

Answer 3

Get the engine straight up and down. Remove the two drain plugs. One is just above the cavitation plate, sometimes called a vent. And the other is all the way down below the prop shaft. To refill get a pump for the gear lube bottle, it is much easier. Fill from the bottom with both plugs out, ensuring all air bubbles are out. Just as the new lube peeks out the vent hole stop and put the vent plug back in. Now get ready to move, unscrew the pump tube and quickly place the bottom plug back in. And..................don't forget the little teflon washers, they keep out the water. Best of luck

Answer 4

BOAT = Bust Out Another Thousand

Answer 5

1964 merc 3.9 starts, runs, dies, as about to shift into gear. Usually have to prompt it with ether to save arm from multiple pulls. Carb is clean. seems lean by spark plug tale. ideas?

Answer 6

ok auto tech here but fisherman at heart. if it has a black box, lol, really then i would replace that, i have seen those go bad all the time and there expensive. there is a way to alter the ignition system but i wont go there in here, sorry

Answer 7

Replace the coils! Sometimes when they get hot they'll shut down when they are old and cracked.

Answer 8

http://www.outboard-motors.us/mercury/ poke around in here you my find you answer good luck

Answer 9

sound like the magnetto get it checked or the compasiter..!!