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Thread: EFI controller

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    Prism's Avatar
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    EFI controller

    Just wondering about the red pot (#3) on the EFI controller. Most of the time, on the setups I've been around, the red pot is always at the stock (#1) position or very close to stock. The instructions say this pot controls fuel delivery for high speed running sort of like a main jet. Being that alot of our boats are seriously modified, the fuel output at high speed must be a total of the fuel added based on the adjustments of pots 1 through 3 not just 3 alone. This is why position 3 is always at or near stock, because positions 1 and 2 are already adding fuel and 3 just tops it off at high speed. Am I right in this assumption? I'm guessing if it were any other way, we would all be lean at WOT with the pot set at 1. To me this makes sense because it is mapped like how a carb delivers fuel. Just was thinking about this and never heard a technical reason as to why this is. Is this logical?


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    Happily Self-Employed WFO's Avatar
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    Quote Originally Posted by Prism View Post
    Just wondering about the red pot (#3) on the EFI controller. Most of the time, on the setups I've been around, the red pot is always at the stock (#1) position or very close to stock. The instructions say this pot controls fuel delivery for high speed running sort of like a main jet. Being that alot of our boats are seriously modified, the fuel output at high speed must be a total of the fuel added based on the adjustments of pots 1 through 3 not just 3 alone. This is why position 3 is always at or near stock, because positions 1 and 2 are already adding fuel and 3 just tops it off at high speed. Am I right in this assumption? I'm guessing if it were any other way, we would all be lean at WOT with the pot set at 1. To me this makes sense because it is mapped like how a carb delivers fuel. Just was thinking about this and never heard a technical reason as to why this is. Is this logical?
    #3 only comes into play when the red light (crossover) comes on.

    The reason it is on position 1 for most non-ported boats is because Yamaha already gave us plenty of fuel for the WOT circuit.

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    Prism's Avatar
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    Thanks WFO for your response. I was hoping you would be one of those who answered this question. Let me rerphrase myself with an example. Lets suppose the settings on an EFI controller are 3-3-1-7. Just hypothetically speaking, lets say injector pulse width at 7150 rpm with the red light on is 200 milli seconds. If I were to change EFI settings to 9-9-1-7 (only low speed and accel richened) does the injector pulse change on top too even though setting 3 is the same? Example, does the duty cycle change to 300 milli seconds at 7150 rpm even though position 3 remained the same? I'm not trying to overthink this but I find it hard to believe a 1300 with FF, Sonic booms, d-plate, head work, and porting require no more fuel up top than the stocker. Lets assume there is enough fuel, wouldn't the stocker then be pig rich and foul plugs every time you opened one up? If the EFI system was a MAF system or even a closed loop system and could tell how much air was actually entering the engine, then I could see it be "self adjusting" in a way. But this is not the case with our systems. I'm just honestly trying to grasp this, and am probably missing some piece of the puzzle.
    Last edited by Prism; 10-04-2007 at 03:01 PM. Reason: typo, added a sentance

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    Prism's Avatar
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    I just re read your response. I guess ported boats are at a setting higher than one, but the ones I've seen have never been set higher than like two or so. Does this sound correct? I guess Yamaha really did put alot of fuel in there up top. I bet I'm thinking there is more airflow gained than there actually is when it comes to smaller stuff like F/A's and d-plates. Thanks for the help. I guess it works just how it says it does.

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    RUNWME's Avatar
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    Is there a way to turn on and off the power to this from a switch? So when running normally, its left off, but if you suddenly got exceptionally good air and needed fuel for 45 additional horsepower, you could switch it on ?
    Oh... uhmmmm yeah, that exceptionally good air could come out of a bottle

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    Since we dont have a MAP or MAF to adjust fuel based on engine load or volumn of air coming into the engine, we have to rely on the TPS to calculate for engine load. The controller is changing the duty cycle based on where you put the controller, and the crossover (#4) is turning on the high speed circuit at your desired rpm. I have learned by playing with the controllers that a higher setting on the idle circuit (#1) will richen up or carry over to the accelleration circuit (#2).

    The high speed circuit is pretty rich from the factory. Hell, we have tested boats with VFIII reeds and no controller and they held together. You must forget everything you know about 4-strokers for a minute. Fuel actually cools a 2-stroke motor. Thats why I always add extra water cooling to these motors when I modify them. The controller is the biggest help in the transition from cruise to WOT, and idle to WOT circuits.

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    Prism's Avatar
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    Good stuff. Thanks for your thoughts. I can't wait to see the results of your 1390 EFI. If I wasen't so far away I'd have you set up my 1390 when the time came. You sure can make a 1300 FLY!! The 1390 should be insane!

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    I think I can find a little more speed in the 1300s. I still have boxes of parts to test.

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    Is there anyone using a higher setting on #3? I have mine set at 6-6-6-9.

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    My son (mohawk man) jeffsntx's Avatar
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    6 on the third pot is pretty high from what I have seen and heard. I am a newbee with the EFI stuff and I dont have mine dialed in exact yet but think its going to be a 1 or 2.

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