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Thread: to slow with no go

  1. #1
    killer beazz
    ive resently installed 77 150hp merc out board to my 16 ft carlson challinger tunel with an 8in jack plate my problem is it wont run over 40 mph my rps at wat 5500 this is an on going problem befor i had a 105 chrysler that would only run 40 mph so i changed moters hoping this would give me more go any sugestions would be help full i expeced to run 60 mph at least ????????????????????

  2. #2
    Yes, you should see at least 60mph, probably closer to 65 mph. I will assume that this is an in-line 6 cylinder Mercury 1500 outboard as that is most likely the case.
    First thing first, what prop are you using? Diameter and Pitch? Stainless or aluminum?
    Suggestion....running a tunnel with a jack plate, you need a stainless propeller.
    Next, do you have a water pressure gauge. You need one, it is a must. I don't know the in-lines as well as the v-6 motors, but I am going to say you need at least 12 lbs. of water pressure.
    Next, if you don't have a nose cone with low water pick up, this will definately help. I would assume that you do have one though if you are running a jack plate.
    The prop could be the problem. I couldn't imaging running an aluminum prop near the surface. The vibration would have to be terrible.
    If you have done all this, it has to be the motor? Compression check? Carbs?
    Good Luck

  3. #3
    killer beazz
    a stanless prop is my next purchace i am curently runini a 13/17 alum prop water presur is good the tatel tell stream is strong but i do not know wate a nose cone does ?? as fore the prop i just wanted to make sure the moter wase runing ok all 6 cilinders have good compresion

  4. #4

  5. #5
    Killer, with that prop you will never get much over 40 mph. Exactly how high do you have your engine. as far as a low water pick up the few times i have installed a pickup on an line it slowed me down, and most people i have talked to have had the same experience, try to keep it just high enough to still get good water pressure, Sounds to me like you need a good stainless surface peircing prop, when you start running a 17 pitch aluminum on a raised engine you are asking for trouble. also if you are using an 8" jack, then install some rigid motor mounts. Also I would think that with that 17 pitch your RPM would be higher than 5500. My '72 1400 merc inline turns 5600 with a 21 pitch.

  6. #6
    Yes those were exactly my thought as well. How high is your jackplate set, if memory serves me i think you can go 1 1/4" up for every 2 inchs back.

  7. #7
    You are running exactly what you should be running with 17" pitch. 5500 rpm and 17" pitch = 42 to 43 mph. If you put 12" boat trailer tires on a Corvette it probably won't go 100mph either! You need to be running at least 24 pitch at 5500 to get in the low 60mph range.

  8. #8
    killer beazz
    thanks fore the help i am gona pick up a new stanles steal prop tonight 21 pitch

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