Yamaha 70 2 stroke vs 75 2 stroke

[sutor623]

Hey guys, my boat is rated for a 75hp. I noticed that the 70hp 2 stroke has a block displacement of 51.8. The 75hp steps up BIG to a 69.6 block, which is the same block as the 90hp. For an extra 30lbs of weight it seems very worth it.

Here is the issue. I have a very nice 70hp Yamaha that I would like to look at. I am just wondering how in the world that little block can produce 70hp??? My guess is that the 70 is working much harder to produce 70hp vs the 75. This is going on a 1754 welded tracker aluminum boat. We use it to tournament fish and will have lots of gear and a big bait tank on board. I want as much torque as I can get. How much better do you guys think the 75 will perform? Should I just keep waiting? These 70-75hp 2 stroke engines in good shape are very difficult to find.

 

[flyingscott]

I would not worry about the 51 cid block making 70 hp Evinrude did it for yrs out of a 49 cid block. I would go for the 75 hp personally because it will probably have a better torque curve. My dad has owned the 90 hp yamaha since 1985 to present and it is a wonderful motor. But either motor would be a great choice and I think you would be happy with either. Is the yamaha a C75 by any chance as that was their budget motor. I like the Yamaha motors because they disproved the opinion that 3 cylinder motors cannot idle well.

 

[sutor623]

Thanks Scott!! I have always had an infatuation with Yamaha motors. Heck, my Merc 60 EFI has a Yamaha powerhead and I love it. I like the newest pre-etec 75 triples because they used a 56cid block. I havent seen any 75 yamahas floating around but I will tell you this 70 that I am going to look at looks brand new. Owner says it has under 100 hours on it. It a 2000 model. Dont think I can pass this one up!

 

[flyingscott]

Thanks Scott!! I have always had an infatuation with Yamaha motors. Heck, my Merc 60 EFI has a Yamaha powerhead and I love it. I like the newest pre-etec 75 triples because they used a 56cid block. I havent seen any 75 yamahas floating around but I will tell you this 70 that I am going to look at looks brand new. Owner says it has under 100 hours on it. It a 2000 model. Dont think I can pass this one up!

I run an 1986 70 hp evinrude I love it's a great motor. I don't know about the yamaha 75 on the 69 cid block but the 90 is not a low end beast by any means.

 

[jimmbo]

Myself I prefer larger displacement engines, more low end grunt and load reserve.

 

[99yam40]

A 17 year old motor that only has 100 hours on it has set a lot, running less than 6 hours a year
hope they stored it properly between run times

 

[mphelle8vld]

^^^
Really good point, hopefully there's a pile of empty cans of fogging oil nearby.

 

[sutor623]

A 17 year old motor that only has 100 hours on it has set a lot, running less than 6 hours a year
hope they stored it properly between run times

Yes sir I have been thinking a lot about this. It may have actually turned me off of the motor. The motor is not locked up but I am pretty sure it hasn't been run in years.

 

[sutor623]

Even if the motor is free, the rings can still rust and become brittle right?

 

[99yam40]

The C40 I bought 3rd hand had rusted main bearings,
required a rebuilt crank shaft and gaskets and seals along with a few other things.

sitting for long periods can allow rust to start on bearings , races, crankshafts, cylinder walls and rings and other shiny surfaces inside the motor if not stored properly.

My brothers 25 evenruid locked up due to moister getting into a cylinder because the exhaust port was open over the winter. just bad positioning of the piston

 

[sutor623]

Wow that's crazy!