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Results 1 to 9 of 9
  1. #1

    Default Mercury 2-Stroke 50 HP , RPM Question

    I recently purchased a 2008 Tracker with the 50 HP 2-stroke. This is my first 2-stroke outboard. The moter runs fine but seems to be taching very high. At 12 to 15 MPH is 6,000 to 7,000 RPM normal or should it be lower?
    No smoke from the engine, runs and idles smooth, just seems to be high RPM

    Thanks in advance for any help or advice antone can offer.

    Marc

  2. #2

    Default Re: Mercury 2-Stroke 50 HP , RPM Question

    7000 RPM is too high. Is that wide open?. Does it sound like it's really winding out? The tach could be on the wrong setting or you could have the wrong prop. What kind of boat is this and how fast does it go?

  3. #3
    Join Date
    May 2010
    Location
    Sebastian ,Fl
    Posts
    1,740

    Default Re: Mercury 2-Stroke 50 HP , RPM Question

    Also what was it on before?If it was on a pontoon the prop could be the wrong one.Or the prop hub could be spun.
    Get a Tiny Tach and hook it up.That's a tool that is always a good thing to have.J
    boats . net worst place to buy parts.
    Get towing insurance.Great investment.
    88 Bayliner with twin 85's

  4. #4

    Default Re: Mercury 2-Stroke 50 HP , RPM Question

    Quote Originally Posted by Dockside Marine Repair View Post
    7000 RPM is too high. Is that wide open?. Does it sound like it's really winding out? The tach could be on the wrong setting or you could have the wrong prop. What kind of boat is this and how fast does it go?
    It's a Bass Tracker Pro Team 175, I bought it from Bass Pro in MD. The prop is original and looks great, no scratches or bends. I keep it in the garage and used the Stabil in the fuel. The top speed is 20 mph, maybe 25. I noticed the Tach issue last season on my last run.
    How can I tell if the problem is fuel seperation?

  5. #5

    Default Re: Mercury 2-Stroke 50 HP , RPM Question

    Sounds like you have the wrong prop. I'm guessing that boat shoud do at least 25, probably better than 30. The speedometers are rarely accurate but if the boat struggles to hit 25 all wound up you need a prop with more pitch. We'll need to consult the Board on this one because each boat and motor combination calls for a certain prop. Ideally you would want a prop that turns 5500 solo, trimed out. I would think that prop would be a 15 pitch at least. Possibly up to 17 pitch at the most. That's just my guess but a guy who has rigged many boats like this would know for sure. There should numbers on the side of the prop. Could you have a look and tell us what those numbers are? If you don't find any numbers on the side look into the back of the prop around the prop nut.

  6. #6

    Default Re: Mercury 2-Stroke 50 HP , RPM Question

    The prop has 816704A40P13 Mercury on the side
    There is a number stamped on the washer behind the prop nut, 16
    2008, MERC50 ELPTO 2 Stroke
    If you recommend a different prop, let me know the number. If there is something I can buy to repair the speedometer or improve it's performance let me know. If I run the motor and keep the RPM's below 5,000 it will be well below 1/2 throttle.

  7. #7

    Default Re: Mercury 2-Stroke 50 HP , RPM Question

    I believe that's a 13 pitch. I know that same engine on a 20 ft. pontoon boat typically uses a 12 pitch so I'm pretty sure your way off. 13 pitch means that theoretically 1 revolution of the propeller will propel the boat 13 inches, you lose approx. 10% depending on speed, load, and hull efficiency (never mind that). The general rule is 1 pitch is worth about 200 RPM but I find that calculation to be accurate only when you're close to your optimum prop size. You might try a 15 to get you close but there is still the possibility of tach. and speedo inaccuracy. Someone at Bass Tracker should know exactly what prop to use.

  8. #8
    Join Date
    Jan 2010
    Location
    Posts
    664

    Default Re: Mercury 2-Stroke 50 HP , RPM Question

    Here is some general information out of the S/M to help you go by.

    Mercury/Mariner 50 HP (3 Cyl.)
    Wide Open Throttle RPM: 5000-5500
    Recommended Transom Heights : 15”, 20”, 22-1/2”
    Right Hand Rotation Standard
    Gear Reduction : 1.83:1
    Diameter Pitch
    No. of
    Blades Material
    Approx.
    Gross Boat
    Wgt. (lbs)
    Approx.
    Boat
    Length
    Speed
    Range
    (mph)
    Propeller
    Part Number
    10” 19” 3 Alum Up to 1100 Up to 14’ 41-49 48-73146A40
    10” 17” 3 Alum Up to 1400 Up to 14’ 35-43 48-73144A40
    10” 16” 3 SS 1200-1500 Up to 15’ 32-40 48-91818A5
    10” 16” 3 Alum 1200-1500 Up to 15’ 32-40 48-73142A40
    10-1/8” 15” 3 SS 1300-1800 13-15’ 28-37 48-855862A5
    10-1/8” 15” 3 Alum 1300-1800 13-15’ 28-37 48-73140A40
    10-3/8” 14” 3 Alum 1400-2100 14-16’ 25-34 48-816706A40
    10-1/4” 14” 3 SS 1400-2100 14-16’ 25-34 48-855860A5
    10-1/4” 14” 3 Alum 1400-2100 14-16’ 25-34 48-73138A40
    10-1/2” 13” 3 Alum 1600-2600 14-17’ 21-31 48-816704A40
    10-3/8” 13” 3 SS 1600-2600 14-17’ 21-31 48-855858A5
    10-3/8” 13” 3 Alum 1600-2600 14-17’ 21-31 48-73136A40
    10-3/4” 12” 3 Alum 1900-3200 15-19’ 18-27 48-816702A40
    10-5/8” 12” 3 SS 1900-3200 15-19’ 18-27 48-855856A5
    10-5/8” 12” 3 Alum 1900-3200 15-19’ 18-27 48-73134A40
    10-7/8” 11” 3 Alum 2200-4300 16-21’ 14-24 48-85632A40
    11-1/4” 10” 3 Alum 2500+ 17’+ 11-21 48-73132A40
    11-5/8” 11” 3 SS 2200-4300 16-21’ 14-24 48-823478A5
    11-5/8” 10-1/2” 3 Alum 2200+ 17’+ 13-23 48-827312A10
    12-1/4” 9” 3 Alum 3000+ 18’+ 8-17 48-87818A10
    12-1/4” 9” 3 SS 3000+ 18’+ 8-17 48-97868A10
    12-1/2” 8” 3 Alum 3500+ 20’+ 1-14 48-42738A10

  9. #9

    Default Re: Mercury 2-Stroke 50 HP , RPM Question

    Well there you have it in writing. That actually looks like reliable information. I must have been mistaken. You can calibrate the tach by changing the pole setting in the back. Lay down in the boat so you can see the back if the tach. If you can't fit you'll have to remove the dash panel to access the back of your gauges. Look for a small plastic adjusting screw. It should look more like an arrow than a screw and has a few numbers around the outside of the arrow. Use a very small flathead screwdriver to gently rotate the arrow to different settings until you find one that more accurately corresponds to the engines RPM as you believe it to be. Do this with the engine running. You'll notice one setting may read way faster while another reads too slow or doesn't respond accurately to increasing throttle. Look for the setting that reads 800-1000 RPM at idle. Usually the wrong settings are quite obvious and one or two settings may appear very close to what would seem accurate. Remember what setting it's on now so there is no confusion between two possibly correct settings.

    As far as the speedometer there is no adjustment but, I find that the pressure line that gives the speedo it's reading is in many cases pinched or kinked somewhere and sometimes in multiple areas as it makes it's way from the rear of the boat to the dash panel. The zip-ties that secure all your wiring and control cables will often squeeze this tiny hose as it is too soft to be very tightly secured. This is very common.

    There is the possibilty of a spun hub but, I don't feel it is likey since the prop appears to be in good condition and they usually get a lot worse pretty quickly once the hub has failed, soon rendering the prop useless and rarely is a prop with a spun hub able to get a boat on plain. Many times you cannot see a spun hub by visual inspection unless it has been badly spun of has had to limp a long way home after it has failed. Sorry to have steered you wrong on the prop pitch, I'm more accustomed to seeing 50's on pontoon boats and usually 4-stroke Bigfoot models. Oddly enough I don't see very many Bass Trackers.

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