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  1. merc850

    Motor only fires up when key is turned to off

    You can't see the problem because it's usually in the electronic circuitry that's why you have to use the pdf troubleshooting guide.
  2. merc850

    Motor only fires up when key is turned to off

    The merc switch is a safety device not needed for regular operation. The pdf will tell you what will happen. When you get it running don't rev the crap out of it on the driveway - keep the revs about half throttle.
  3. merc850

    Motor only fires up when key is turned to off

    You can also have a friend hold onto the spark plug wire while cranking.Ha Ha trick or treat! Recheck the timing (should have mentioned that first).
  4. merc850

    Motor only fires up when key is turned to off

    That system uses a trigger that is located in the distributor and one sign that it's bad is the problem you are having. Are all the wires in good condition no bad insulation or copper? Remove the mercury switch wire from the switchbox and see if it will start. Remove the distributor cap and look...
  5. merc850

    Motor only fires up when key is turned to off

    Identify the ignition system from these 2 diagrams.
  6. merc850

    1978 Mercury 500/50hp help!!!

    Look for Mercury Marine 1975 thru 1978 C-90-75512 the break in mix is 25:1 the run mix is 50:1; your motor should've be broken in years ago.
  7. merc850

    Mercury artwork

    I have created some artwork that's Mercury themed and is available from Fine Art America (https://fineartamerica.com/) just type Murray Dowding in the search box; you can get 15oz coffee mugs, T-shirts, puzzles, shower curtains etc. Here's the latest shirt I received - the edges are not...
  8. merc850

    1975 Mercury 650 starter issue

    Put your voltmeter on the battery terminals and turn it over - then put it on the starter terminals and turn it over, the voltage should be the same (approx. 11v) if it's low the battery is weak or the solenoid connections are not clean.
  9. merc850

    Starting and maybe restoring old Mercury 402 40hp

    The Merc 400 motor that preceded it had crank breakage problems due to owners over propping them which caused them to run under the rpm range, ie lugging; the fuel pump was water cooled to reduce the possibility of vapor lock and the mercury switch prevented overreving if the motor hit an...
  10. merc850

    08' Merc 90hp --Ditching The Oil pump/going mixed fuel..

    If you don't have a tach get one and make sure the motor is running near the hi end of its operating range at full throttle.
  11. merc850

    Mercury adjustment question

    Usually you have to have the motor running to shift into reverse, on land you turn the prop while shifting to line up the shift "dogs".
  12. merc850

    Mercury Mark 20

    Maybe someone has already changed it or Mercury dealer did, the serial Nr. is what you use for parts ordering and a service manual. The Nr. makes it a 1954. Remove the drain screws in the LU and see what comes out.
  13. merc850

    Mercury Mark 20

    The early versions used a 2 hose fuel line, the crankcase pressurized the tank which pushed fuel into the carb; this can be changed to a single line like the later ones - ask these guys http://johnsoldmercurysite.com/phpBB3/index.php?sid=c1eedb7960442074f2594ee023b0274f one important note: the...
  14. merc850

    Mercury 402 40hp 1970s prop unit removal

    I had the same problem with my 850, the carrier would not come out and the housing was damaged trying to remove the internals; I used a cutoff wheel to cut it in half and saved the gears and propshaft to use in another case. Another way is to buy a complete dead motor with a good LU.
  15. merc850

    Power Trim (A-45194A13) Question

    According to the manual "The reverse lock knob must be turned fully to the left before uncapping valve ports or oil will drain from the pump"! This is for removing the lines. You could also remove the cylinders which is what I'd do as it is easy. You could undo the lines from the cylinders and...
  16. merc850

    1973 85 hp Needs Ignition Help

    Here's the wiring diagram for the 4 cyl. engines, the BROWN terminal is for the Merc tach [NLA] check the timing belt to see if it is OK ie; turns the rotor, don't pull the plug wires out of the cap - they screw in. Do not try to pry off the rotor in the dist. it is molded on - you can clean the...
  17. merc850

    Mercury 402 40hp 1970s prop unit removal

    Here's a still from a video I shot of my 850 running in forward.
  18. merc850

    Mercury 85hp runs fine on Muffs but Boggs down in Sea

    Please don't rev it up to full throttle in the driveway, more that 2000 rpm's with no load can be destructive.
  19. merc850

    Mercury 402 40hp 1970s prop unit removal

    I'm afraid you are going to have to replace that LU because you have taken a piece out of the area where the exhaust goes into the prop. It will leak and cause cavitation and loss of speed.
  20. merc850

    Mercury 110 9.8 no-start

    That ignition relied on the points making contact to trigger the spark, if they are clean and set properly they should fire a plug. I don't have the gap setting info sorry.
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