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  1. merc850

    Spark Plug Half-Fouling

    Looks like a weak spark caused by failing stator or trigger. See if the spark will jump a 7/16" gap. Do not use regular reach plugs unless manual says so, they will hit the piston top.
  2. merc850

    No spark on Merc 85hp

    Are you following these steps? https://forums.iboats.com/threads/starting-a-2-cycle-merc-verified.670882/
  3. merc850

    1968 20hp lower unit seals

    A manual would help but in lieu of one I'm posting some starter pages: (before you start soak the cover nut area with a penetrating oil for a few days too loosen it up.)
  4. merc850

    No spark on Merc 85hp

    One marine starting battery not a deep cycle one.
  5. merc850

    Waiting to launch

    Almost launch time (except in canada) and many guys will be changing their impellers re-installing their lower units and having shift problems: This is how I do it in about 60 sec.: Turn the LU shift shaft by hand counter-clockwise until it stops, then with Vise Grips tight on the bottom of the...
  6. merc850

    No spark on Merc 85hp

    If you put a voltmeter on the + starter terminal and the cowl ground read the voltage while turning over the motor, it should be 10-12 volts if your battery is good. If it does fall in this range your starter probably needs rebuilding/cleaning (brushes). A small engine electrical shop could fix...
  7. merc850

    Merc outboard serial number question

    Good that you've worked on one before so you know the plug wires screw into the cap, CDI has the engine harness https://www.cdielectronics.com/product/414-2770/, or Marine Engine.com I bought the last one Mercury had this year
  8. merc850

    1965 3.9hp plug fouls

    I don't know what brand of oil you're using but I've found that Amsoil synthetic smokes less and if you live in the US you can get 100:1 blend which lets you go from 50:1 to 100:1. I was mixing it at 70:1 and of course I used less oil and reduced smoking.
  9. merc850

    Merc outboard serial number question

    i think you should rewire it - there seems to be some incorrect connections and corroded wires which can cause a major fire. I am wondering about the connections on the terminal block in image 2 they look like they are coming from the stator but one disappears into the cowling and one is...
  10. merc850

    1965 3.9hp plug fouls

    The Nr. refers to heat range - The middle number indicates the heat range of the spark plug, the higher the number the hotter the heat range the hotter the plug the less it will foul.
  11. merc850

    1965 3.9hp plug fouls

    According to the Merc manual the 1964-66 3.9's used a J7C plug and the gap is .025"/ the points should be set at .020". Your motor falls into those years.
  12. merc850

    1965 3.9hp plug fouls

    That's not the right plug for that motor - J8C https://www.oldmercs.com/category_s/1208.htm
  13. merc850

    Mercury 85HP Thunderbolt Ignition Series??? Whats missing??

    Found this wiring dia. appears that those motors used ADI not a distributor.
  14. merc850

    Mercury 85HP Thunderbolt Ignition Series??? Whats missing??

    I'm guessing that the fuel pump/wiring harness/ignition can't be used in your motor, go have a look at it if you can with cowling off. It might be a 1979 model like this one
  15. merc850

    Mercury 85HP Thunderbolt Ignition Series??? Whats missing??

    Correct! serial numbers 3186263 thru 3493912 were 1972 models.
  16. merc850

    Mercury 85HP Thunderbolt Ignition Series??? Whats missing??

    I have my 850 runner on a boat and I picked up a poorly maintained one for $200.00 which gave me some useful parts, some marinas keep old ones in the "boneyard".
  17. merc850

    Mercury 85HP Thunderbolt Ignition Series??? Whats missing??

    Try John's Old Merc site.
  18. merc850

    Mercury 85HP Thunderbolt Ignition Series??? Whats missing??

    Wiring diagram fuel pump parts the pump originally had brass fittings that the lines attached to (compression type) that are missing from your lines so you'll have to use barb fittings and you'll need the pump body; these people https://www.oldmercs.com/category_s/1702.htm sell the hoses and...
  19. merc850

    1975 Mercury 500EL Lightning Energizer wiring…

    That motor uses a self energizing "magneto" so the white wire just powers the choke and tach as shown in the wiring diagram - it doesn't need 12v to operate. And as Chris said the control harness can be used for many HPs this is the wiring for 8500/1250/1400 etc the white engine harness wire...
  20. merc850

    Did I flood it, did I mis use the remote, was it old fuel, or all of the above?

    Tip the motor all the way forward and fuel will run out of the carbs.
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