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I'm a long way from being able to purchase a replacement engine for my 1979 22' Revenge, but out of curiosity how much more efficient are the new 4 stroke engines compared to the old two strokes?

The reason I ask is that I took my boat out for its longest shakedown cruise to date last weekend. I guess we were out for about an hour. Keep in mind I was using an external 12 gallon fuel tank rather than the internal tank and started with 10 gallons. The only additional weight was that of my wife and myself. No gear, no dogs, no ballast, no coolers full of ice cold beer unfortunately.. :) Anyway we averaged probably about 3500 RPM, would occasionally bump her up to WOT. After getting back to the dock and checking the tank I'd guess she burned about 8 gallons.

This is the largest outboard engine I have owned so I'm not really knowledgable enough to know if that rate is average for this engine. Does that fuel rate sound about right for a 225 HP two stroke under those conditions and can you fathom a guess at how much fuel I'd burn under the same conditions with a newer 200 HP four stroke?

Thanks!

John

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Yamaha now has a 200hp 4 stroke that is only 4 cylinders so its really light. Likely over 100lbs lighter than yours. Also the new motors are crazy quiet. Not sure what the increase in mpg but I would think easily 50% better.

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John -

Your fuel use sounds accurate.

Carb'ed two stroke motors burn a lot of fuel at idle and low rpm's. Four stroke and DFI two strokes burn much less. AT WOT, the difference is significant but not gigantic.

I would agree with Brian changing to a 200 hp DFI or 4 stroke will result in an overall fuel savings of 50%

The decision to re-power tends to be for more than just fuel savings. To recover the costs of a re-power (vs staying with a carb'ed 2 stroke) one would have to own the boat for 10 years and run 100 hrs a year.

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Brian and Phil,

Thanks for your replies. That's an amazing increase in fuel efficiency but as you say it would be hard to justify the cost for just that. My wife would argue as she can't stand the smoke. Wouldn't want to breathe it for too long but it does not bother me. Smells like a 2 stroke.

I checked the gear oil Monday and there was no evidence of water or metal which is another real plus because the L/U is so eaten up from life in the salt water, there would be no way I could tear it down to replace seals or gears. We would be talking L/U and maybe mid-section replacement and would probably be another reason to go with a new or used 4 Stroke at that point.

Good to know that my current fuel burn is about right though. I was beginning to wonder if I had missed something when I rebuilt the carbs last year. It runs great from about 1500 to WOT 5500 or so. Runs rough as a cob at idle to 1500 but I think that is sort of par for the course for those big old engines if I recall correctly. I am still running some oil in my fuel while trying to assure myself the oiler is working correctly so that probably has a lot to do with it. The oil in the tank is slowly decreasing so I think I'm OK there. Next time I take her out I will probably throw in a new set of plugs and skip the pre-mix.

Thanks again!