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Operating range 2012 75hp 4stroke Mercury

F

Fred Long

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I am being told by dealer to run 15" prop and don't worry about it. I think this isn't right. the operating range according to the Mercury book is 5000 to 6000 and I am turning 6300 according to my tach. He says the tach is probably wrong but the whole rig is new and I'm not buying this. I know it operates best in the upper range but I think I am over reving it at 6300. I know it has rev limiter but I don't trust that either, I just want to protect my new engine.
 
Hi Fred,
If Mercury say 5000-6000RPMs,go with it.They don't tell you that for the fun of it. Go for a 17p and that will bring you in to the top end of the scale and keep your warranty intact.
Or borrow a known good tach and compare.
OR throw a half dozen crates of beer into the boat,the extra weight will bring the revs down as well, and take your time coming back to the ramp:D:D

PS Follow the break in procedure to the letter.Helps with warranty claims,God forbid, you need to.
 
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haventaclue said:
Hi Fred,
If Mercury say 5000-6000RPMs,go with it.They don't tell you that for the fun of it. Go for a 17p and that will bring you in to the top end of the scale and keep your warranty intact.
Or borrow a known good tach and compare.
OR throw a half dozen crates of beer into the boat,the extra weight will bring the revs down as well, and take your time coming back to the ramp:D:D

PS Follow the break in procedure to the letter.Helps with warranty claims,God forbid, you need to.
Click to expand...

Tks, will heed your advice. Just needed some assurance. I like the beer idea too.

F Long
 
Just leave it. Over-propping will kill the engine quicker. A lot quicker. And the holeshot will be weak with a taller prop.
 
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17" pitch sounds great haventaclue has a clue should bring rpm to the 5900rpm range giving your boat a better hole shot and higher top speed if tach is correct what tach do u have sc1000 system tach?? If so should have digital read out as well
 
You don't hold her wide open all the time, right? If you cruise her down in the 4,500 rpm range you won't hurt the motor. A blast at WOT for a few seconds above the red line now and then is not a good idea, but it'll take it if you don't abuse it. And, as stated, plane off with these punchless, mid-range torque 4 strokes need all the help they can get.

Jef
 
[/QUOTE]He says the tach is probably wrong but the whole rig is new
Take it back and tell him you want it replaced under warranty.After all he sold you the rig and he's the guy that's telling you that it's wrong.;)
As Jeff says you don't hold her wide open all the time,but some do,even before break in procedure is completed.
So let me pontificate for a little while.
Prop size is governed by the manufacturers recommended RPMs.And keeping within that range depends on the weight of boat,it's contents, how the boat is trimmed.
So if Fred has his boat loaded with his buddies,beer and gear and is running at 6300,he needs more pitch
On the other hand if he is loaded with his buddies,beer and gear and is running at 4900,he is over propped.In fact I would say,IMHO,if he was running at 5000,I would still say he was over propped.
But again as Jeff says,most people cruise in and around the 4500.And believe me,Jeff,timebandit and others know a dam site more than I do when it comes to outboards
Click to expand...
 
Fully loaded boat getting 6300 rpm would definatley need right pitch prop for all around performance and fuel economy. if u are crusing atonly4500 rpm with a 17 pitch propu will have greater speeds at that rpm or less rpm at the same spoed increasing fuel economy
 
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