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  1. roger3645

    Nagging problem w/850 merc cutting off

    Okay I’ve had this issue with this motor since last summer and it’s driving me nuts. 1975 850 85 hp merc. Problem is it’ll just cut off while approaching high rpms and then it’ll start right back up. What I’ve done so far: Removed and cleaned carbs, ran 3 treatments of sea foam thru it. I’ve...
  2. roger3645

    Need 2 props for 2 boats

    Okay here goes. I’ve have two boats and yes the wife says one has to go, but I only have one old 2 blade bronze prop (13.5 x 19p) to share between them and the pitch is low for both boats.<br /><br />#1 1977 16’ Tri-hull fiberglass bass boat 850 lbs dry weight. Powered by a 1975 850 85hp merc...
  3. roger3645

    Sea Foam and Compression Results

    1975 Merc 850, has good compression in all cylinders except #3 which was at 90 PSI. After 2 sea foam treatments #3 is now a bit over 100 PSI and other 3 remained about the same. Should I give it another sea foam treatment? I have not had it in the water since treating the motor with sea foam...
  4. roger3645

    Driveshaft Swap 650 into a 850

    Have a 1973 850 with a pitted driveshaft. I'd like to know if I can swap out the 850 shaft with a shaft from a 70's model 3 cylinder 650.
  5. roger3645

    LU shift shaft bushing removal 75 850

    The shift shaft on the lower unit of my 1975 850 merc turns freely without engaging any gear. It's currently in fwd. How do I remove the bushing that secures the shift shaft? Do I need a special tool or can I tap it in the notched areas with hammer and screw driver?
  6. roger3645

    850 merc jumped the red and white post power pack

    I’m running a 1975, 850, 85 hp mercury. I previously posted that I’m having a problem with the motor cutting off at WOT. Also there was a humming or clicking noise coming from the area of the key switch in the control box. It was suggested that I use a jumper wire to connect the red post to the...
  7. roger3645

    1975 850 merc just cuts off at WOT

    I’m running a 1975 850 85 hp mercury serial #4300733. Yes and I’m very glad that it still runs as well as it does. The only problem I’m having is it will just cut off. This occurs at WOT. It will run for a while at WOT then just shut off. Just like flipping a light switch. It will start right...
  8. roger3645

    2 bladed prop to 3 blades

    I'm running a 1975 merc 85 hp (Still runs good) it has a 19 pitch 2 bladed prop. I want to change it to a 3 bladed prop. I read somewhere when adding an additional blade you should drop the pitch down. If so, I should drop down to a 17 pitch prop. Does this sound right to anyone else?
  9. roger3645

    2 bladed prop to 3 blades

    I'm running a 1975 merc 85 hp (Still runs good) it has a 19 pitch 2 bladed prop. I want to change it to a 3 bladed prop. I read somewhere when adding an additional blade you should drop the pitch down. If so, I should drop down to a 17 pitch prop. Does this sound right to anyone else?
  10. roger3645

    Flat Spot 850 Merc

    Have a 1975 850 85hp merc. At about half throttle the engine will start to bogg down an shut off unless I squeez the priming bulb. Then it will start to pickup speed and I can give it full throttle. I replaced the fuel pump last year.Any ideas on this one or should I just get a longer fuel line...
  11. roger3645

    Thunderbolt Tach hookup

    I have a 1975 850 mercury and have just picked up a vintage thunderbolt tachometer made in the same year as the motor. The control box has the tach plug with the brown black and white wire. I don't have the wire harness to just plug in the tach. I want to hard wire to the wires in the control...
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