115/80 four stroke vs 90/65 two stroke jet

[bingman]

Contemplating on buying a 115/80 yamaha jet for my 17'9" northriver scout. I currently have a 90/65 two stroke. I know there will be a weigh increase with the fourstroke but I'm wondering if I will see much of a power increase? Just wondering if anyone out there has been in the same situation?

[cohoho]

How does the 90/65 run right now? Other than reliability and easy starting I bet you do not experience too awful much of a difference.  Slight extra weight but extra HP so the hole shoot will probably be the same...   How does the North River start off right now?  Back drop or is it level on take off? 

I experienced going from a 50/35 Honda (run anywhere-in any water and shallow- but slow- top end 24mph) on an 18ft ATEC flat bottom with tunnel, to a Honda 90/65 - jumped up like a raped aped top end about 37-38mph...  Then I used a 90/65 ETEC, while the Honda was in the shop - top end 45mph - holy mother of god that thing had power like nothing else ever!  I could run as fast as some of the big boys in the 350's and 454's...  but could go where they never dreamed of.......   For the jet- do not over look ETEC, will out perform the Yamaha hands down- atleast in JET configuration...  Had same Honda 90/65 on my Wooldridge 17ft Alaskan w/tunnel after the other boat - top end 35mph..

Also - rule #1 in a jet - Drive it like you stole it!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[wildmanoutdoors]

You will have cleaner burning, nice and quiet. But have you seen what a 115 4 stroke weighs? Jets are weight based as to planeing and such. Go over, or near that thresh hold and you gonna be a slug. I think it will be a push for power after you add a 400 pound motor.

You should read up on these factors on outboardjets.com

I have a 19 foot flat bottom. In 05 when I repowered and rebuilt everything I looked at a 115/80 Yamaha. I opted for the Bombardier direct inject 175 v6 2 stroke. Weight at 420 and massive more power at 130 HP at the pump. You never smell it and it gets awesome fuel efficiency.

My boat is very light, and a rocket ship to drive.

The difference between a 65 and an 80 is 400 more pounds of payload. But your going to gain near 200 pounds just in the motor swap. So it will likely get you a bit more power, but is it worth the 8 to 10 g's?

[bingman]

Thanks for the input guys.

My 90/65 flys with me and one other guy in it, but if i add another person and gear it slows it down dramaitcally. The back really drops down out of the hole when i have more than a couple of people in it. The only reason that I am considering the 115/80 is because its a smoking deal and its only going to cost me $500 to upgrade. I called northriver and they said the boat is rated for a 135 hp. I looked up the weight difference and is going to add an extra 170 lbs but going to the four stroke.

[full choke]

How does the 90/65 run right now? Other than reliability and easy starting I bet you do not experience too awful much of a difference.  Slight extra weight but extra HP so the hole shoot will probably be the same...   How does the North River start off right now?  Back drop or is it level on take off? 

I experienced going from a 50/35 Honda (run anywhere-in any water and shallow- but slow- top end 24mph) on an 18ft ATEC flat bottom with tunnel, to a Honda 90/65 - jumped up like a raped aped top end about 37-38mph...  Then I used a 90/65 ETEC, while the Honda was in the shop - top end 45mph - holy mother of god that thing had power like nothing else ever!  I could run as fast as some of the big boys in the 350's and 454's...  but could go where they never dreamed of.......   For the jet- do not over look ETEC, will out perform the Yamaha hands down- atleast in JET configuration...  Had same Honda 90/65 on my Wooldridge 17ft Alaskan w/tunnel after the other boat - top end 35mph..

Also - rule #1 in a jet - Drive it like you stole it!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Cohoho- what year was that ETEC? I had a 06 90/65 on the back of my 18' flat bottom and I could only muster 32mph. Granted my boat was built kind of heavy, but it was flat and smooth. I loved that motor, never had any mechanical issue whatsoever in the six years I had it. Incredible hole shot, horrible on fuel with the pump, but flat out dependable. But I could never get 40mph out of that thing, not even downhill...

[wildmanoutdoors]

To get to 45 mph with a 90/65 the boat, motor and driver must not weigh over 500 pounds.

My boat is a very light built 19 foot flattie with a 175 V6 and it barely can hit 45 on a good day.

Full chokes setup and speed is much more in the realm of a 90/65.

Many indian guides I fish around all have 16 to 18 footers with 90/65 Etecs and none run those kind of speeds.

[cohoho]

To get to 45 mph with a 90/65 the boat, motor and driver must not weigh over 500 pounds.

My boat is a very light built 19 foot flattie with a 175 V6 and it barely can hit 45 on a good day.

Full chokes setup and speed is much more in the realm of a 90/65.

Many indian guides I fish around all have 16 to 18 footers with 90/65 Etecs and none run those kind of speeds.

Well I guess you were in the boat with me weren't you???  I know through GPS my recent Thunderjet could run 45-50mph, my buddy had identical boat in AK and couldn't shake me off his wake going down river of the Big Susitna- only can go off that as I didn't bring my video that day....  Did I take picture of the GPS- nope I didn't. Can only go off what is left of my memory.  So if I am off a mile or two, sue me... Get over it..

It was an 1860 ATEC boat with 2 inch tunnel, boat weighed nothing and small center console and just my fat ass minus 40lbs ago.....  I got a couple pictures with the 50hp, but none with the ETEC.

That boat would plane level, float level and run level- no drop ever!    Not going to get that out of anything of likes of Roughneck, G3 or other similar skiffs that people put jets on them and hulls aren't designed for them...