Old outboard efficiency vs newer

I have a couple of older outboard 2 stroke motors. Both need some work. The lower mileage one is an Evinrude fastwin 18HP of about 1971 vintage. It has good comrsssion and hasn't ben run in years. (Put away properly )
The other is a 20 H Merc about from about 1995.
Assuming they are running well, how much more fuel are they likely to consume (% wise) vs a newer tech 2 stroke or 4 stroke?
How much more do they pollute the lake?

These motors will see use on a 15 aluminum utility boat.

Tia.

New motors are heavier than most older motors.---Yes they run nice and save fuel.----That all comes at a cost.---Consider a 25 hp e-tec and fuel injecters are $400 each and are not plug and play items.

racerone said:

New motors are heavier than most older motors.---Yes they run nice and save fuel.----That all comes at a cost.---Consider a 25 hp e-tec and fuel injecters are $400 each and are not plug and play items.

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Yes, that is a turn off. If you go to a recent non injected 2 stroke, do they have much improvements in efficiency vs the old 70's motors?
I really have to educate myself on these motors. I know most boat shops seem to imply an old motor is worthless and not worth repairing (At $100 per hour)
I have done complete automotive engine rebuilds, but have never worked on a boat motor, so hopefully you don't need many specialized tools to make a repair if it needs it. I'll know more about the Merc engine when I get it later this week. (Free with the purchase of a cottage!)
Had a bad impeller supposedly and started to run very rough before being shut down. Might be toast I guess.

The 71 model 18 hp is a super motor. -------Cheap to own and operate.------Parts are cheap and everywhere for them.

Well thanks, Will be getting this one from a friend next week and have a look. Hopefully one of them can be made to give reliable service.

What racerone said, the 18 is a great motor. But your question was how does it compare with a new 4-stroke in efficiency and emissions. If that is your priority, then the new one wins hands down.

I like the mariner 20 hp myself they are really good strong engines and will be more powerful than the 18 evinrude. A compression test is a must on the 20 hp mariner. But the evinrude is also a great motor and will be cheaper to fix. I compare them this way if you look at the purchase price of a newer motor compared to what you have. The price difference is quite a bit of fuel for the old motor and could be a big enough difference that the older motor will be cheaper to run. I am not sure that the new motors at the prices they are at will ever pay for themselves in fuel mileage.

Are these motors quick to strip down to examine cylinder wear, etc? Just basic tools needed? I have a Yamaha YZ 250 two stroke and a rebuild of the cylinder is a couple of hours work.

Nucad said:

Are these motors quick to strip down to examine cylinder wear, etc? Just basic tools needed? I have a Yamaha YZ 250 two stroke and a rebuild of the cylinder is a couple of hours work.

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If an older outboard is well taken care of you will never see the inside of it. Outboards are generally easy to work on. A newer outboard is a whole different animal anything fuel injected/HPDI/E-tec/Optimax/Verado you are almost tied to the dealer.

I Made a mistake in that the second free outboard is a Yamaha two stroke that had a bad impeller and was making noises when shut down. It pulls over with the feeling of compression. Were old Yamahas any good vs my Evinrude Fastwin 18 HP?