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Results 1 to 9 of 9
  1. #1

    Default 85 Mercury 50 runs but won't open up to wide open throttle and has weak hole shot

    Motor starts and runs fine at idle and mid range but under load / in gear will not open up to wide open throttle and plain out. I just replaced the stator, trigger, and switchbox, cleaned the carbs, and tried a new fuel tank system and fuel. I had no spark on second cylinder before ignition parts but now have spark on all four. With only me in the boat today I was able to reach wot or close to it but it took way to long to get it there and with passengers I was not able to come even close. I checked the throttle linkage at the motor and its opening all the way. It feels like about 1/2 to 3/4 throttle when wide open. Just no power. Before the ignition parts replacement it did nearly the same thing, no wot.
    Any help would be much appreciated.

  2. #2
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,657

    Default Re: 85 Mercury 50 runs but won't open up to wide open throttle and has weak hole shot

    You might simply be over-propped.

    Jeff

  3. #3
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,852

    Default Re: 85 Mercury 50 runs but won't open up to wide open throttle and has weak hole shot

    Reed valves checked ??-------------Also any compression test results.

  4. #4

    Default Re: 85 Mercury 50 runs but won't open up to wide open throttle and has weak hole shot

    How do I check the reed valves? I did a compression test and it read about 80 psi on all cylinders. My tester is very cheap so I will be rechecking tonight with a different compression tester. Is 80 psi too low?

  5. #5

    Default Re: 85 Mercury 50 runs but won't open up to wide open throttle and has weak hole shot

    One other thing I should note: Before it changed or replaced anything I took it out and it started and idled rough and I was not able to get to wot. After about 15 minutes of running with the throttle lever wide open but engine not opening up it suddenly cracked open and took off to wide open and full speed. I ran it for ten minutes or so then I shut it off and started it back up with no problem it took right off and ran wot for the rest of the time is was out. I thought maybe it just had bad fuel so I switched to a different tank with fresh fuel and it did the same thing where it wouldn't open up. I only spent about 5 - 10 minutes this time and did not really get it hot so it never did open up for me. I then checked spark and found no spark on cyl. 2 and weak spark on cyl. 1 so I replaced all the ignition parts and cleaned the carbs - which I suspect was unneccessay because they were nice and clean when I took them apart.
    On the troublshooting guide that came with the CDI ignition parts it say the the rectifier can cause weak hole shot so I plan to disconnect it and try another run tonight.
    Thanks

  6. #6
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,852

    Default Re: 85 Mercury 50 runs but won't open up to wide open throttle and has weak hole shot

    Reed valves are found internally in the motor.-------They should actually be open when comression is taking place in the cylinder.------A partial inspection can be done when carburetor is off.------------I would be checking for a bad ground on the ignition system since you say it " instantly " opened up and took off.-----Perhaps run with a timing light to see if it is ignition related.

  7. #7
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,657

    Default Re: 85 Mercury 50 runs but won't open up to wide open throttle and has weak hole shot

    It's NOT the reed valves! Been messing with Mercs for 50 years and have NEVER seen a reed valve problem.

    I can't believe anyone would run a motor that wasn't working properly at WOT for 15 minutes! It'll be a miracle if there's any compression left in that motor (that was having carb issues). I suggest you get a compression test before doing anything else.


    Jeff

  8. #8
    Join Date
    Sep 2006
    Location
    Baton rouge, La, USA
    Posts
    1,731

    Default Re: 85 Mercury 50 runs but won't open up to wide open throttle and has weak hole shot

    is timing advancing on this motor?i seem to remember a grease fitting for that....i had two of these motors but of an earlier vintage and this is a problem if the thing aint greased...and can be intermittent ......

  9. #9
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,657

    Default Re: 85 Mercury 50 runs but won't open up to wide open throttle and has weak hole shot

    Good point on that grease fitting, but this is not a distribtor motor.

    Jeff

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