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Author Topic:   70 HP on a 17'
Bob Gilmore posted 08-27-2001 11:31 AM ET (US)   Profile for Bob Gilmore   Send Email to Bob Gilmore  
Can anyone tell me how well a 70 HP Yamaha would power a 17' Super Sport Limited? I have the option of putting a 70 on mine. I would like to know how well the 70 might work?
Macman posted 08-27-2001 01:10 PM ET (US)     Profile for Macman  Send Email to Macman     
Check the previous 2 mos. on the Performance thread. There is a post about a 70 Yamaha on a Montauk. This should answer most of your questions.
Bigshot posted 08-27-2001 02:12 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Ditto! What are you running now?
Bob Gilmore posted 08-27-2001 04:57 PM ET (US)     Profile for Bob Gilmore  Send Email to Bob Gilmore     
Running a 1990 Johnson V4 90. It does pretty well but it's older and smokes some and is not as fuel and oil efficient. Plus the Johnson weighs more. It appears that the 17' SS Limited has more of the interior weight aft than a Montauk. I think the lighter 70 would drop the bow down some. The 70 HP Yamaha is on another boat of mine. I can swap it out if it's a good move.
Bigshot posted 08-27-2001 05:01 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
As long as top end is not your main concern. It will get way better gas milage and will change the way the boat handles due to less weight. If you normally cruise high 20's etc, great move. I have the 90hp yamaha and would honestly be pretty happy with a 70 if the cards were dealt that way. Good Luck!
Bob Gilmore posted 08-28-2001 09:38 AM ET (US)     Profile for Bob Gilmore  Send Email to Bob Gilmore     
Top end is not that important but it's nice to have there if you need it. I like a smooth easy cruise at about 25 mph and without the motor straining to push it and without alot of noise or vibration. The dealer told me the Yam 70 was 226 lbs, and the Yam 90 was 261 lbs, a difference of 35 lbs. My SS Limited has the typical dual fib console/windshields but has the thick heavy mahogany seats, hatch and console trim with an 18 gal plastic Pate. I know it's a little heavier than the regular Montauk. I'd like to know the weight of the current Johnson 90 on it now. The Yam 90 should cruise a little easier and with less revs at 25 mph than the 70. After reading alot of the old posts, I'm still on the fence as to the Yam 70 or Yam 90. Decisions, decisions.
Tom W Clark posted 08-28-2001 09:53 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
The Johnson 90 weights about 300 lbs. and is, all things considered, a great motor.
ValkariaKid posted 08-28-2001 10:30 AM ET (US)     Profile for ValkariaKid  Send Email to ValkariaKid     
I have an '88 Johnson 90 V4 VRO, on my montauk, and looking at the book it lists the weight of the engine as:

Man. tilt - 288 lbs.
Pwr. tilt - 301 lbs.
Pwr. tilt - 306 lbs. Extra long shaft.

Will the extra weight of the 90 make that much of a difference?


Bob Gilmore posted 08-28-2001 11:06 AM ET (US)     Profile for Bob Gilmore  Send Email to Bob Gilmore     
A tip of the hat and a sincere thanks you guys for all the info. What a resource this is.


JBCornwell posted 08-29-2001 09:19 AM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Howdy, Bob. I have a 2001 Suzi EFI 4 stroke DF70 on my '80 Montauk. The prop is a 18" SS. Cruise at anything from 25 to 30 is easily attained without exceeding 5000rpm, and if I need to hurry she trims out to 5800rpm at 38mph (gps). My son's 2000 Montauk with a Merc 90 2 stroke and a 19" SS prop performs about the same except he can get 40 mph in a hurry. Needless to say, I use a little less than half the fuel.

I would expect your 17 SS to perform about the same.

BTW, I had to use a 4" fixed jackplate to make the mount fit the transom. It probably contributes to my performance numbers.

Red sky at night. . .
JB :)

Bob Gilmore posted 08-29-2001 11:02 AM ET (US)     Profile for Bob Gilmore  Send Email to Bob Gilmore     
Thanks for the info. I cruise and fish but do pull a skier now and then. Changing to the Yam 70 2 stroke would lighten the transom by about 75 lbs over the 90 Johnson, a considerable weight difference with a definite effect. The forum posts indicate the 70 would do fine but the little extra from a Yam 90 would be good to have. Wouldn't it be great to be able to test drive it both ways with no cost or trouble, ha ha. This great forum gives you the next best thing to an actual test drive.

... and a motor that's right... sailor's delight.

Thanks again,


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