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    Plug color on Merc flat plugs?

    I have run 15 gallons plus through my old Merc 150 at speed and the plugs still look new and clean except part of the gap is darker where the spark travels. The metal is wet with gas and clean, so is the tip. The piston looks to be the correct brown color below the plug, and the five I can see...
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    Merc HP ratings change in 70s?

    I read here Merc went to prop hp ratings and the 140 became a 115. Does that make my 1973 150 inline6 more like a 120hp? If I run my boat on Mercurys prop calculator with the size & weight of my boat, it comes out to about what a new 120-125hp would do speed and prop-wise. <br /><br />The owner...
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    Old Merc inline 6 OB owners-props recommended?

    Sorting out a '73 150 on a lighter 17'. Can you suggest a prop? I get 5200-5400rpm with a stock alum. Merc 21 and little bow lift. I have no pad on the bottom and my cavitation plate is about 2" above the bottom. Motor has been raised about 1.5" to this position. Manual says 5300-5800 rpm.<br...
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    Merc 150 I6 1973 Prop/speed? for 17' boat

    Does anyone have a Merc inline 6 can you tell me what prop you have and speed?<br /><br />I have a 17 Checkmate and I am thinking 21-23 prop. Also, do they run best at 5800rpm like the manual says? I have to set my tach yet and am trying a 21. Tach is not right now and I am getting a test tach...
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    1973 Mercury 150 HP inline rpm/speed ?

    I have a '73 Merc 1500 'Tower' I bought last summer. I went through the whole fuel system first then new impeller, fuel line & pumps, plugs, normal tune & clean, ran in the dark, cle aned carbs twice, etc. It is on a 17' Checkmate and was stored the last 8yrs or more. I have 120psi +/- 1lb...
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