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Folks , I've been shopping for a new motor for my boat.
I had decided on a new Yamaha 4-stroke 90 hp. The dealer is trying to convince me that the boat would run nearly as good with a 70hp. I would save the 130lbs difference in weight getting better fuel econony than the added 20hp between the two motors. He has both motors ready to install. The difference is
$1000.00 even, Give me your opinion.
Thanks,

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I think you may have already answered your own question, unless you "have the need for speed". Had my dealer proposed a Honda 70 instead of a 90, I would have given it serious consideration for the very reasons you mentioned. My wife & I have both had spinal surgeries, and though we're fully recovered, we cruise comfortably and rarely if ever use the top end or the powerful hole shot, though it's there if I want to. I'd say take your savings and get Sea Star hydraulic steering and a whole lot of fuel. One Man's Opinion! Good Luck.

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The speed difference is ~ 5-7 mph between the two.

The weight difference is significant. With the 90hp you have almost 1 extra person in the boat.

I don't have calm water so speed is not a goal. If you have flat conditions and want to go 40 mph with your family all day long, get the 90 hp. If you plan to tow a slalom skier who is "hefty".

Otherwise the 70 is great.

Just an opinion.

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Thanks, The boat will be used in and around Mobile Bay and the rivers that connect. Occasionally the Intercoastal. I'm probably better off with the 70hp as my speed days are over.

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I have a '78 Montauk with a 2000 Evinrude (Suzuki) 70 4 stroke. The motor runs great. I am not a speed demon, so it is fine for me. I must confess that I am always looking on ebay for a 90 E-Tec though.
A couple of things to think about:
With a Suzuki, the 70 and 90 are the same block. The extra hp comes from fuel injection differences I guess.
My motor has a timing belt (model year 2000). I believe the new ones use a timing chain.
An E-Tec has fewer parts, is lighter, gets the same (or better) fuel economy, meets the same emission requirements, and is just as quiet.

I am not complaining about my 4 stroke, just reflecting.

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I don't know what the dealer means by "...nearly as good".

The F90 will be faster and more powerful but its weight is really pushing the limit of what the Montauk was designed to support on its transom. The F70 is a much better fit weight wise but will be slower.

If you are concerned about taking water over the transom in sloppy conditions, the F70 will be superior.

If you want to go as fast as possible, the F90 will be superior.

If cost is a concern, the F70 will be superior.

For most uses the F70 will be more than adequate but it is your decision what is best for your needs.

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We had a 90 Merc on our Montauk back in the 80"s, and found that power level to be ideal for the east side of Vancouver Island. I also spent a lot of time on 17' bare hulls with tiller 60hp Yamaha's. The 60 was just ok with a light load, but was easily slowed when extra weight was aboard.

My vote would go to 90hp, but as all the engines are so good these days, I'd choose the lightest 90 whose colour I could live with.

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Yikes...just had a look at various engines and see what you are up against. ETEC 90 is the lightest at 320...The Suzuki 348 and the F90 is 369, the others are heavier.

I would still go with the 90 though. Many ran 90's plus a kicker back in the day...so must have been pushing 400lbs then anyways.

Our 90 could get more boat out of the water, so we could get a bit better ride than with the smaller engines. The hits were pretty sharp on the forward sponson area on the lesser powered boats...though of course we know "ride" isn't exactly a Montauk strong point.

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I got the F70 for my '68 Sakkonet which has been rebuilt more like a Montauk with an enlarged casting deck, center console w/forward built-in seat to house a 15gallon tank. Everything is moved forward to help with the weight in the rear which was a real problem.

I posted on here about 2 weeks ago due to matching the prop. The dealer eventually put a 13.5 x 15 K-series Yamaha aluminum prop on. I'm getting 26.5 @ 5000rpm and topping out at 6000rpm and 32mph. No idea on fuel economy yet.

As a comparison my friend repowered his '86 Montauk with an F90 and it sits real low with the aft scuppers actually below waterline. Even though his has a much faster top-end he never uses it. The boat porpoises way too much and some of that is the extra rear weight. He still cruises his @ 27mph albeit at a lower rpm. This has lead to more fouling problems due to running it at those lower rpms and the dealer is actually suggesting decreasing the size of his prop so it will cruise in the 5000rpm range. End result, he'll be running his F90 like my lighter F70. I'm happy with my F70 but I use it primarily to fish, no tubing or skiers.

I also had the Sea Star hydraulic steering installed and it's a blessing considering I am so used to the power steering on my 28 Grady.

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As most know, I'm a fan of more power on a Montauk, since I installed a Merc 115 in-line 6 tower on mine, but weighing only 300#.

But if your interest is in a mid-range 4 cylinder 4-stroke, here are a few things to consider. The Yamaha F70 is built on the same block as the Yamaha & Mercury 50's and 60's. These engines all use the same powerhead, and no one seems to know who makes them, a well kept corporate secret between Yamaha and Mercury. But the powerhead short block is the same.

Anyway, the only explanation for the addtional 10 HP of the Yamaha F70 is 4 valves per cylinder, vs the others with 2. Whether that makes the additional 10HP over the 60 is the issue. Remember, Yamaha tends to have a history of over-rating HP and this one could be the same, a clever marketing move. The 32 MPH reported by the owner above seems to indicate not much improvement, if any, over a Merc or Yamaha EFI 60.

We have seen reports that a Merc 60 EFI can move a classic Montauk about 34/35 MPH. Boston Whaler reports that a brand new 150 Montauk, a boat which weighs EXACTLY the same as the old classic Montauk, runs 35.1 MPH with the Mercury 60 EFI 4-stroke Bigfoot.

I guess what I am saying is, if you want lower HP, consider the 60 of either brand, I'm betting it's a better investment for maybe 1 MPH top end, or maybe no additional top end at all. Boston Whaler sells a lot of smaller boats with the 60 EFI 4-stroke and it seems to be extremely well received. The 60 should run about $5500 for the engine, well bought.

For these smaller engines, you will also have to determine if you should buy the regular gearcase or the Bigfoot gearcase. Boston Whaler installs the Bigfoot models.

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Here is a list of Current Motors and their Weight.
http://www.whalercentral.com/articles...ticle_id=5

Lightest in their class:

90 HP = Evinrude E-Tec 90 @320 pounds

70 HP = Yamaha F70 @257 pounds

I had a 1985 Evinrude 70hp and a 1988 Evinrude 8hp kicker on my prior Montauk 17'.
Evinrude 70hp was 248 pounds
Evinrude 8hp was 58 pounds
Total = 306 pounds

If you ever plan on having a kicker motor you may want to go with a 70 hp main motor.
Just something to think about and keep in mind.

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I have a F90 on my 1984 Montauk. It will do 43 mph on flat water. It does do some porpoising, but it can be easily trimmed. The fuel economy is outstanding for fishing and trolling. It is also very quiet.

Cons: it is heavy but the scuppers are above the the waterline, even with a F6 kicker on it. The batteries are in the console. It is a little scary taking water over the stern when trolling down wind...

Overall, I think this is an incredible engine that is really well suited for this boat. Sure, I would love to have it be 100 pounds lighter. I would never give it up for an F70 though.

Couple of pics in the water...

http://i384.photobucket.com/albums/oo...050769.jpg
http://i384.photobucket.com/albums/oo...050770.jpg

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Mb466. Your boats stance looks great in the water with your 90. When I was in the market for a Montauk, I wouldn't consider anything less than a 90hp motor. Of course I usually have more than myself on board too. I want a boat to quickly get on a plane and go without hesitation. With a 70hp, if loaded up, the Montauk would take a while to plane off......at least the Montauks w/70's I've been on did.

One doesn't always have to use the power they have just because it's there.....but IMO its nice to know you have that extra power just in case it's needed.

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I like having the extra power of the F90 for getting on a plane, which it does quickly. I rarely run at full throttle. Anything over about 35mph seems like it is breaking the sound barrier. Wide open, it is thrilling, but feels on the dangerous side. Add in some chop, and you might shake out some of your teeth fillings.

If considering the F90 and a kicker engine, you need something light. I tried a F15 and F9.9 which were both too much weight for the stern. The F6 is pretty light. You only lose about 1.5mpg dropping from the F15 to the F6, but you drop at least 60lbs of weight. I only keep the kicker on when I am going on open water, like crossing the Chesapeake bay.