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  1. #1
    Race, wreck, repeat delagem's Avatar
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    Tricking the EMM? MSX140

    I've been thinking about how to "rejet" a FICHT motor. Normal tricks on fuel injected bikes won't work due to how the FICHT injectors work. So I was thinking about how to fool the emm into thinking the air was more dense.

    Apparently for every 5 degrees Farenheit temp drop, air becomes 1% more dense. a 4% increase in density could be achieved by making the computer think it was 65F instead of 85F, as an example.

    I needed to change my air temp sensor due to the lovely design of the F/A on the 03 and early 04 MSX140's. So, I brought the F/A baseplate inside from the garage, shot it with my Raytek and took resistance readings every 5F. At 65F the resistance is 936 ohms. At 85F the resistance is 1040 ohms. I did every temp from 45 to 85 just to ensure it's linear. It's not, but close enough.

    Hooking resistors in parallel will create lower resistance. formula is R = (R1 × R2) / (R1 + R2)

    Long story short, if I hook a 9300ohm resistor in parallel with my Air Temp Sensor, it should trick the emm into thinking air is 4% more dense, and add 4% more fuel.

    Am I thinking clearly? Any flaws with this?


  2. #2
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    That sounds logical. Perhaps you could use a variable resistor in series to adjust on the fly? With no other changes to what you have now, it should be easy to see how the fuel amount changes with the wash pattern eh?

  3. #3
    Race, wreck, repeat delagem's Avatar
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    Unfortunately no. If I'm understanding correctly, FICHT motors don't develop the wash patterns like normal 2 strokes, as the fuel doesn't come in thru transfer ports, it's injected from the center of the head. Dunno really, I've only owned the ski a month, and haven't ridden it yet.

    If what I've read about lack of normal wash patterns is correct, it makes it a PITA, eh? I was talking with Randy about monitoring EGT's, but he didn't seem to think it was worth it.

  4. #4
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    k447 is going to be one of the best Sounding board,Bernie also should have some input of ideas. How are you figuring on increasing better air flow?

  5. #5
    Race, wreck, repeat delagem's Avatar
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    Quote Originally Posted by Keddano View Post
    k447 is going to be one of the best Sounding board,Bernie also should have some input of ideas. How are you figuring on increasing better air flow?
    Kieth and I have been bouncing these ideas back and forth. He's got a different approach than this, though.

    F/A's, Flowrites, reeds, waterbox, that bitchin' exhaust outlet from GPEngineering, I'm not sure yet?

    Michael

  6. #6
    Moderator beerdart's Avatar
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    What type of fuel regulator does the FITCH use??

  7. #7
    Race, wreck, repeat delagem's Avatar
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    Quote Originally Posted by beerdart View Post
    What type of fuel regulator does the FITCH use??
    I don't know, but I think I know where you're going with that! It was my first thought, too until Kieth explained how FICHT works. On the Ducati motorcycles, the injectors can be tricked by raising the fuel pressure; 120milliseconds at 55psi is more than 120ms at 45psi.

    Unfortunately, the FICHT injectors don't work that way, they're a solenoid. Raising pressure only fills the idle injector more quickly; it won't affect the quantity sprayed in.

  8. #8
    Rasta Mon Condoms We Be Jammin!!!!! TxVirageTx's Avatar
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    ???

    and whats the benefit???burning more fuel will cause it to be rich and hurt hp unless its so close to the edge right now its on the lean side as is.or are you considering bigger throttle bodies or triples???either way i believe the real issue was that the fi bodies simple can't supply enough fuel for either upgrade

  9. #9
    Race, wreck, repeat delagem's Avatar
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    Quote Originally Posted by TxPro1200 View Post
    and whats the benefit???burning more fuel will cause it to be rich and hurt hp unless its so close to the edge right now its on the lean side as is.or are you considering bigger throttle bodies or triples???either way i believe the real issue was that the fi bodies simple can't supply enough fuel for either upgrade
    They are reported to be on the ragged edge of lean, due to the impending 2005 emissions regulations. The FI is close to the upper limit, supposedly the injectors are only capable of 10% more than current max.

    I'll take that 10%, if I can!

    I'd love a set of triples! Send them to me, I'll powdercoat them and give them a nice home! The reason I'm looking into this is I simply can't get a set of triples, or pretty much anything else performance-wise for this ski. That, and I don't like being told something "can't" be done.....

  10. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Arrow

    Quote Originally Posted by delagem View Post
    So, I brought the F/A baseplate inside from the garage, shot it with my Raytek and took resistance readings every 5F. At 65F the resistance is 936 ohms. At 85F the resistance is 1040 ohms. I did every temp from 45 to 85 just to ensure it's linear. It's not, but close enough.

    Hooking resistors in parallel will create lower resistance. formula is R = (R1 × R2) / (R1 + R2)

    Long story short, if I hook a 9300ohm resistor in parallel with my Air Temp Sensor, it should trick the emm into thinking air is 4% more dense, and add 4% more fuel.

    Am I thinking clearly? Any flaws with this?
    I would suggest simply replacing the stock sensor with a fixed resistor matching the coldest allowable value.

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