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Author Topic:   New Merc 90
kamml posted 01-18-2002 12:58 PM ET (US)   Profile for kamml   Send Email to kamml  
The new 90 is mounted on the Montauk. The owners manual requires transport in the lowered position. It states that the trim up bracket is not to be used for trailering. Previously I always trailered in the up position. I am really going to like the trim switch on the cowling. The break in recommended by the dealer is two hours of variable speeds, up on plane, up to 2500 rpm for three minutes, back down for three minutes (do this for about 15 minutes. Go on up to 2700 rpm for 3 minutes etc. to around 3500 rpm tops for the first hour. Second hour go on up towards top end in stages, go up hold for three minutes, return back to 2700 rpm, on up to tops speed for three minutes, down to 3000 rpm for the full second hour. Run at least 36 gallons of 50 to 1 premix in conjunction with the auto oiler then straight gas. Return to the dealer after the first 20 hours to drain gear oil and check over motor. When I raced two stroke carts you warmed up the motor and then went flat out from then on in. This obviously more complex machine requires a great deal more time spent on break in. Any advice or suggestions? Ken
Bigshot posted 01-18-2002 01:14 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Usually it is 1st hour under 1500rpm's. 2nd to 5th under 4k but fluctuate every minute or so and an occasional WOT but do not hold it. From 5 hours to 15 or 20 do not sustain WOT. I never sustain WOT on any engine no matter how many hours on it. I might run it Wot just to haul booty for a minute but that is it. If you are the type to run WOT all the time pull it back a couple hundred RPM's and she will last much longer and only drop a couple MPH.
baltica posted 01-21-2002 02:11 PM ET (US)     Profile for baltica  Send Email to baltica     
I just repowered my Montauk 16 Katama with a 90 hp Merc. The hose attachment for washing out the cooling system is a plus, so is the tilt/trim switch on the cowling. Its great having a dependable motor when running out to Oregon and Hatteras inlets!
Some things I've noticed different from my older (1986) Merc in-line 6:
1) a little bit more vibration when idling (even the rails shake), presumably because there are only 3 cylinders (instead of 6).
2) I had a new tachometer installed with the new motor. Using a 19 inch prop, the tach climbs over >6000 rpm when running wide open. I suspect the tach may be miscalibrated, but just to be safe, I've been throttling back (under 5,500 rpm). Since I didn't have a tach before I can't say what rpm I ran the old motor at. Does anyone know, is there any protection on the motor to prevent it from overrevving?
lhg posted 01-21-2002 02:35 PM ET (US)     Profile for lhg    
Baltica - you will definitely need a higher pitch prop. Try a 21" or even 23" standard prop, or better, a 20" or 22" Laser II prop. The Katama is a faster and lighter boat than the Montauk, and most Montauks would run a 20" Laser/High Five with your engine. One of the reasons for the higher pitch prop is the new engine is running a higher gear case ratio (2.33 vs 2.0), which means you need a higher pitch prop to achieve the same speed. Your boat should be quite fast!
baltica posted 01-22-2002 01:33 PM ET (US)     Profile for baltica  Send Email to baltica     
lhg, thanks for suggesting the different prop. Do you think the difference between a standard aluminum 21 or 23 (less than $100) and Laser II is worth the price ($400 plus)?
Thanks, Baltica
Bigshot posted 01-22-2002 02:50 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Buy one on E-Bay but either way, yes they are worth every penny unless your middle name is "Dredger".
lhg posted 01-22-2002 06:27 PM ET (US)     Profile for lhg    
For great prices and quick shipping on any new Mercury prop, try offshoreperformance.com.
I bought 2 Merc Laser II props from them last summer for $365 each, plus shipping, no sales tax. They are in Ft Myers FL. Send them an email for a quote. I was very pleased with their service. I have yet to find better pricing on any Mercury propeller.

If you have a prop to sell, try propswap.com.
Their computer based system works pretty well. You may also find an excellent used prop there, but Merc Lasers are hard to find in the mid-sized gearcase. I sold two Merc Trophy 4 blade props there. The secret is to price yours $5 or $10 less than someone else's same prop. Yours will then go first. The site is popular with the bass boat & go-fast crowd, who use a lot of Merc props.

On a lightweight boat like your 16' Whaler, I wouldn't even consider using an aluminum prop vs. an SS model. Aluminum props are at the bottom of the prop efficiency curve, and are fine if you're never going to run the boat over 30mph (even if it will go over 30). On any boat that will be run over 30 mph, an SS prop should be used. The Merc performance line is for boats that will do over 40mph. Actually, Mercury is telling you what to do, since in the standard 4 1/4" gearcase SS "Vengeance" line, the highest pitch they make is 18". If you need more than that, which you do, you HAVE to get a performance line prop like a Laser or High Five, which begin at 20", creating an automatic transition to the performance line. These props hold like "glue", and simply will not spin out in rough water, sharp turns, etc.
They are also necessary if you are running at elevated transom heights.

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