1977 Mercury 850- 4 cyl Thunderbolt Ignition

visar08

Recruit
Joined
Jul 18, 2019
Messages
1
I am having problems locating spark plug wires on line. The wires thread into the distributor. I am hoping someone can give me some advice. My motor is a great potable water engine. Meaning in the driveway with muffs, no issues. In the water, as soon as I shift into gear it dies. If I play with the warm-up lever and throttle and hit it perfectly it will take off and run fine. Back to neutral it does the same thing. I want to replace the wires, cap, (bottom section) and carbon? piece that makes contact with the rotor. Also the component where the distributor wire connects to the ignition coil (I assume that is what it is). I know this sounds lame, I don't have a repair manual, bout the motor off an add and sounded great with very good compression, so I was not happy when I finally took it out and realized it only liked my home water and a hose. I first thought I had a fuel problem and corrected part of that. Found out the primer bulb could not keep up with the fuel demand. Replaced with a high flow primer bulb, changed gaskets, etc on the 6 gallon tanks, all that is good. Again main problem is from idle to going into gear and dies. So a minor tune-up is my first shot at fixing the issue. I hope for advise and am I on the right track?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,137
OK, if your motor has a distributor, it is not a 1977, but 1975 or older. Search on "tiger Tails" to find the speak plug wires. That is what some sites called them.

Try to get the crimped on screw threads, and you can install the springs and boots yourself.

Try the surplus unlimited web site or the old mercs web sites, for the tiger tails. Distributor caps are $100 plus, and almost never wear out. The carbon electrode may be replaced for $2 or so. The rotor is not-removeable, and will cost $200+, to replace, if you break it. They are very fragile.

Clean up the brass electrodes with 220 grit sandpaper, carefully to avoid removing too much metal.

Stalling at idle is very common. It is usually dirty or mis-adjusted carb idle mixture. You should probably get a service manual if you do not have one.

Inspect your engine wiring harness, They are usually bad by this point. One can be had at the above web sites.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,263
Do not replace ignition parts unless they are proven defective.---These parts are well made , not cheap.
 
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