Johnson 70 2str to Yamaha 90 4s?

I have a question. I have a 1650 Lund fisherman with a 2000 Johnson 70 two stroke. The max horse rating is 90.
What would a trade over to a Yamaha 90 4stroke do for me?
My 70 will push the boat at 32 MPH at WOT. The 70 has a 17inch prop.
Are the 90 yamahas any good?
I do like the vintage 70 Johnson. Mines still like brand new. Last of the OMCs`. Will fuel economy and preformance of the Yamaha justify the cost?.

Re: Johnson 70 2str to Yamaha 90 4s?

your engine is only just broken in. you have to consider the weight difference in the motors, the maintainance on the 200 (well not necessarily 200) extra moving parts. oil changes, and bla,bla,bla. actually i don't the the extra hp is worth the amount of $$$ involved. with proper care, that engine will out live you. i love running the 1950's engines.

Re: Johnson 70 2str to Yamaha 90 4s?

heres a vid that explains the difference in 2 and 4 stroke

http://www.youtube.com/watch?v=viWhxvo6DLk

that 90 4 stroke would not be any faster then that OMC johnson 2 stroke.and theres a number of things you can do to that johny to get more power they are vary siple and easy to work on.them OMC were one of the lightest outboards ever build so you could always take that 70 and put it on a lot smaller boat and still be under the max transom wight.you can also check to make sure AV plate is at the right hight you could be loosing 1-4 mph from that.and you could go with a steel prop and get another 2-5 more mph.you should check your RPM to make sure you have the right prop set up.if you would like to go to a 90 HP heres a link to a remanufactured 90 HP OMC johnson it was completly rebuild so its just like new and it comes with a 1 year waranty here it is ----

http://cgi.ebay.com/ebaymotors/2002...egoryZ111124QQihZ006QQitemZ160119881626QQrdZ1
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when race time comes you will never see a 4 stroke

Re: Johnson 70 2str to Yamaha 90 4s?

Thanks for the replys. I was mainly thinking about fuel economy with preformance secondary. I do like the OMC 70s`. They are somewhat rough starting and idling. The Johnson 90s` are great motors but I`ve heard they like their fuel too. My 2000 motor was put in service in 2001. Since then I probably burned 7 gallons of oil in it.
We have a new Yamaha dealer were I live. So I was courious about a swap.
Where I fish its an average of a 10 gallon fuel consumtion for a trip. So speed and economy do help with long runs. I will more than likely stick with my Johnson. I do like the new motors smooth running though. I`m also an OMC fan as well. I`m just thinking about my motor no being longer in production among the other things. I imagine parts won`t be an issue for many years to come? If OMC were still in business it would be a no brainer. Dealers of OMC now Bombardier seem to be dwindeling down a bit.

Re: Johnson 70 2str to Yamaha 90 4s?

I wouldn't worry about a parts supply for your 70hp engine, there will be parts avalible for the next 50+ years for that popular engine. What RPM's are you turning with that 17 pitch prop, 32mph seems a bit on the slow side for that size Lund with a 70hp on the back unless thats with 3-4 people aboard. My parents have a Fisherman 1700 with full windshield which is rated for a 115 and when they had a 70hp suzuki 4 stroke on it she would do 35-36mph empty and 32mph with 3 people and fishing gear.

Re: Johnson 70 2str to Yamaha 90 4s?

Rancherlee said:

I wouldn't worry about a parts supply for your 70hp engine, there will be parts avalible for the next 50+ years for that popular engine. What RPM's are you turning with that 17 pitch prop, 32mph seems a bit on the slow side for that size Lund with a 70hp on the back unless thats with 3-4 people aboard. My parents have a Fisherman 1700 with full windshield which is rated for a 115 and when they had a 70hp suzuki 4 stroke on it she would do 35-36mph empty and 32mph with 3 people and fishing gear.

Click to expand...

At WOT I`m running at 5500 RPM trimed up. I was toying with the idea of trying a 19 inch prop. I`m pretty sure the 19 would be too big. This is my GPS speed wich is close to my speedometer.

Re: Johnson 70 2str to Yamaha 90 4s?

I would stay with a 17 pitch then, you don't want your rpm's lower than 5500rpm trimmed out. You could even find a 15 pitch to try out and get the rpm up to about 6000rpm with a light load (just you aboard) you might even pick up a bit more speed and it will definatly jump out of the hole better.

Re: Johnson 70 2str to Yamaha 90 4s?

I think I`ll stay with a 17 inch prop. I don`t like the idea of running 6000 RPM.
The motor sounds pretty wound up at 5500. I was thinking with a 90 Yamaha I could back off on the throttle and have a decent cruise speed at say a 4000 RPM. Achieving both economy and performance. I do like OMCs` and money is an issue so I think I`ll stay with what I have.
I thank you all for your opinions. Iboats is a gold mine of knowlege. Its also fun to post an opinion (Right or wrong) to help someone out or to look at something from a different angle. Even if corrected by those who may know better.

Thanks guys.