Powering a slippery cat with 20 hp. Fuel injected or carb.

Discussion in 'Outboards' started by Russell Brown, Feb 15, 2020.

  1. Russell Brown
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    Russell Brown Junior Member

    What is better? My friend put over 10,000 hours on a Yamaha 20 and I see more Yamaha's than any other outboard. I think they are reliable motors, I'm just surprised that nobody can compare fuel consumption between a carb model and a EFI model.
     
  2. Richard Woods
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    Richard Woods Woods Designs

    I read that the EFI would be better across the range. But then I may have read that here from David, and he says its a guess...... But on the other hand, why would all the manufacturers invest in efi engines if they were not better? The only bad reason I can see is if they know they cost more to service as there's less an owner can do??

    Did you speak to the local Yamaha dealer or head office? I've already commented on my dealings with Evinrude in Seattle

    RW
     
  3. Russell Brown
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    Russell Brown Junior Member

    I think it's about emissions, not just in outboards. I spoke to customer service a few times and begged them to find me someone who could give me some answers. I'm not after hard data, just a rough idea what to expect.
    I don't need it for another month or so, but the older 20 that's for sale might not be available long. What would you do, Richard?
     
  4. fallguy
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    fallguy Senior Member

    Not Richard, but theoretically, cleaner burning engines would be more efficient; unless of course those cleaning efforts were on the exhaust side.
     
  5. Richard Woods
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    Richard Woods Woods Designs

    Obviously neither of us knows much about engines! And so rely on others. (I often talk to Tim Poustie but he's in Vancouver). I'm in a slightly different position than you because when building a prototype I try to experiment so that I can tell future builders what works and what doesn't. It's proven expensive for me over the years!!

    One problem is that your boat, like mine, is such a niche market so no one bothers to do any sensible testing. Especially in the US where fuel is so cheap everyone can afford to run huge engines. You might be better looking at European data maybe?? And have you tried other fora like hulltruth etc??

    Not sure of your time scale. But what I'd do first is see if I could borrow a Yam 20 from your friend, or elsewhere. And then do careful tests with that on your new boat. Although I assume the Yam your friend has is not the same model as currently available??? Yamaha in particular seem to change models very frequently

    Then I would be aggressive to a efi engine dealer (I know thats hard for either of us to do) and say "the Yam 20 usesXgal/hr at Yrevs, is yours better? I'll buy it if it is. Money back guarantee if not" and see what happens. Definitely you want to get the dealer to loan you a couple of props so you can reach the right revs at WOT

    But the normal thing people in our position do is get the engine supplied by an agent one trusts. So there are more Suzukis and Evinrudes in the Bahamas for example than anything, maybe more Hondas in Fl, more Yams in the PNW. Virtually no Evinrudes in the UK, but lots of Yams/Mercury/Marina/Tohatsu. (all usually variants of the same engine of course). Length of warranty is probably also a major factor for you. But the main thing is finding a local dealer who is interested in your project. What does Brandon say??

    Sorry not much help, I've been through the same process and not found the answers I wanted either. So good luck

    Richard Woods
     
  6. DCockey
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    DCockey Senior Member

    I said "guess" because I can not be certain that the EFI engine will use less fuel than the carbureted engine at part throttle and part load conditions. Perhaps I should have said "more likely than not".
     
  7. DCockey
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    DCockey Senior Member

    I would be extremely surprised if anyone at Yamaha US has the information needed to definitively answer Russell's question about the relative fuel consumption of an EFI vs carburetor 20 HP engine on Russell's boat.

    Fuel consumption for outboards is not as simple as a single number, not even a single number for a given engine speed. Even if the engine speed is fixed the fuel consumption will vary with load, and the load at a given engine speed will depend on the boat and propeller characteristics. To compare fuel consumption for Russel's application "engine maps" for both engines would be needed along with an estimate of the boat's resistance vs speed through the water. An "engine map" has contours of fuel consumption divided by power plotted with engine speed on one axis and engine torque or power on the other axis. Engine maps are frequently available for maine diesel engines but I've never see one for an outboard.
     
  8. Barry
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    Barry Senior Member

    Yamaha has an F25 at 126 pounds, they say the lightest 25hp on the market, efi etc,
     
  9. Russell Brown
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    Russell Brown Junior Member

    Thanks for all the feedback everyone. I'll probably go for the EFI F-20 just so that I can hope there's a difference. I have data from a boat we owned with the carburetor version and similar engine loading as the new boat. The EFI version is 13 lbs heavier at 130 lbs (long shaft remote version without trim/tilt).
    I just today remembered that we ran out of gas on lake Champlain on the boat we owned with the old version. Maybe that's a sign.
     
  10. DCockey
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    DCockey Senior Member

    The current Yamaha 20 HP and 25 HP engines appear to be the same except for the power rating. The 20 HP probably has a restrictor plate to limit the airflow and thus power at wide open throttle (essentially the same as a throttle stop would do). The 25 HP would probably allow a slightly higher pitch prop and still reach rated max engine speed at wide open throttle. The slightly higher pitch prop would drop engine speed at the same boat speed and possibly result in a fuel saving. For the same load and engine speed the engines will probably consume the same amount of fuel.
     
  11. Russell Brown
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    Russell Brown Junior Member

    They are the same weight and size and only a few hundred dollars different. I have wondered about the point you brought up and it was on the list to ask about. I do have a bit of time before I have to buy and maybe I will be able to talk to someone about it.
     
  12. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    Time will tell.

    Oh. No. Nobody does that anymore. Measure fuel consumption.
    I guess time won't tell.
    What was the question?
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    The only advantage I see with EFI in smaller engines is greater range for a fixed fuel capacity, I would be disappointed if it was less than 15-20%. With larger boats and engines, the advantage of saving $ can be added to the equation, but I would not bother with a small EFI motor to save $, only to get range where that is critical. The $ spent on fuel would not add up to much, and you need to be more careful with fuel contamination with EFI.
     
  14. Russell Brown
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    Russell Brown Junior Member


  15. fallguy
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    fallguy Senior Member

    The one thing that bothers me about these engine 'options' is many of them share the same block and vary some minutiae of detail that results in the hp rating delta. I believe the F70, 60, 50 are block shared, as are the 90,100,115. So the engines are close within these ranges. For example, for my boat, the F70 was a superb designers choice, but the 90 offers double the alternator which I needed; so then under the block sharing; the 115 is in a similar weight class, but the 115 starts to change the boat..

    One thing I look for in an outboard the size you seek is an engine that operates at lower rpm. For some reason, I just prefer a lower rpm; perhaps a false sense of quieter and longer lasting...
     
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