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Thread: 80's Air cooled bike EFI conversion

  1. #1
    Member darkfibre's Avatar
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    80's Air cooled bike EFI conversion

    One of the thing about restoring an older project bike is the fact that the carbys are 30 odd years old. Having spent most of my career in the automotive trade focused on Electronic Fuel Injection it was almost a certainty with my background that an EFI bike was going to happen.
    In the last 25 years I have been involved in over 45 EFI conversions on cars, some as a complete project, and some just doing the electrical wiring.
    My ‘Pumba’ XJ750 project is only months away from going over the pits and will be on the road for the end of winter. The engine in Pumba is unknown both in condition and mileage but is fine for getting the bike over the pits.
    My spare engine has a known history and is low klms. I have ordered a full gasket set and it will be getting a full strip down and rebuild. This engine will be EFI.


    OK

    1983 air cooled XJ750 EFI conversion.

    Lets start basic and get complicated later.

    An EFI conversion requires consideration of the following points;

    Removal of carbs (DUH)
    Some method of throttle (throttle bodies, one per cylinder on a bike)
    High pressure fuel supply (30psi upwards)
    High flow fuel supply return (more on this later)
    Injectors
    ECU (Electronic Control Unit) to control things that needs the following inputs;
    Engine speed and position (crank angle sensor)
    Throttle position sensor
    Engine temp sensor
    Air temp sensor
    Engine load (air flow or manifold pressure sensor)

    So the start of the project is to do research on what parts to use and integrate into the system.
    Last edited by darkfibre; 28-05-2010 at 09:29 AM.
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    Member darkfibre's Avatar
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    First part of the research finds that a Microsquirt EFI module at $250 fits my requirements and enables the ability to control ignition advance as well as fuel.

    Second part of the research shows that the ignition pickup will need to be modified to work with the Microsquirt.

    More research shows that a fuel pump for the EFI will draw at least 4 amps and needs to be allowed for in the charging system limits.
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    Member darkfibre's Avatar
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    Deciding on R6 components is very easy considering a complete throttle body set up can be bought out of the states for $29 US plus freight if you shop around.

    This pic also shows the diameter of the throttle compared to the original XJ size

    But for the price we now have injectors (don't rate injectors by engine size, rate by HP) Throttle sensor, MAP sensor and wiring!
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    Member darkfibre's Avatar
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    At this stage is a good idea to cut up some old carbs

    Then cross section them to see if injectors can be fitted or how they would work as a throttle body with the venturi machined out;

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    Member D.J's Avatar
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    Interesting stuff, subscribed.
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    Member mcmurray's Avatar
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    Looking forward to the rest.

    I'd like to fuel inject my old CB750 four at some stage.

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    Member darkfibre's Avatar
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    Realizing there is not enough material in the carbs to mount an injector narrows the options.

    The easy option that has been done before is to just adapt the R6 throttle bodies to the engine.
    The problem with fitting a large throttle to an engine with ports/valves that are much smaller is trying to tune it later. Large throttles are overly sensitive at part throttle openings.and can be difficult to tune at light throttle, and wide open throttle from the engines perspective (maximum air flow)
    occurs at 3/4 throttle makes tuning less than optimal.
    So its a no go adapting much larger throttle bodies.

    The option I have decided on use existing manifolds and existing throttles from the carbs, but cut then short and machine out the venturis.
    Injector mounting will be between the head and the original manifolds. Work has started on this idea.

    Last edited by darkfibre; 28-05-2010 at 09:33 AM. Reason: re-edited when sober
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    Member D.J's Avatar
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    Hey DF, will this create a noticable lag of changes in throttle having the extra depth of manifold?
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    Member darkfibre's Avatar
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    Quote Originally Posted by Black Rider View Post
    Hey DF, will this create a noticable lag of changes in throttle having the extra depth of manifold?
    Considering it conforms to most standard EFI manifold designs (most cars have injectors near the head but a SINGLE throttle a long way away from the injectors), and the fact that the first thing to be affected by throttle changes is the throttle position sensor (not the actual air flows inertia) and this can be programmed.
    My answer is it will have less lag than a carb setup. (If its is done correctly) Time will certainly tell
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    Member XSorXpire's Avatar
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    I may have an injector bank and throttle bodies for an old gpz1100 floating around if you want a look.

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    Member darkfibre's Avatar
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    Quote Originally Posted by XSorXpire View Post
    I may have an injector bank and throttle bodies for an old gpz1100 floating around if you want a look.
    I would love to see that set up, but I have committed to a path that follows later designs.
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    No sweat.
    This was the second of the (failed) injection systems after they had started injecting straight into the inlet port(?) and then went back to carbs, so it may not have been much good anyway.
    But i am in Balga if you want a look.

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    Don't be such a pussy, darkfibre - direct injection FTW!!!
    "Once upon a time we would obey in public, but in private we would be cynical; today, we announce cynicism, but in private we obey."

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    80's Air cooled bike EFI conversion

    Well when your finished I'll pay you to do my xj lol

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    Megasquirt is great, its what we used on the Busa, more than capable.

    Let me know if you have any questions, but I think it will all make sense with your experience.

    Also, there are plenty of fuel pump options that draw less than 4A.

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    Member darkfibre's Avatar
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    Quote Originally Posted by nath View Post

    Also, there are plenty of fuel pump options that draw less than 4A.
    I must admit I am having trouble finding a pump with low current draw. At work we have a large range of car EFI pumps but very few with specs.
    Our Sydney branch has a Pierburg fuel pump tester and have tested a wide range of automotive pumps and recorded the current draw. The guys there say virtually no pumps run under 5 or 6 amps once the pressure is up to 30psi.

    The thing to remember is current draw goes up as the load (pressure) increases. No load current draw is irrelevant.

    Do you have any details on possible pumps?
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    Nath's Avatar
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    My bad mate, I double checked all the ones I had in mind, none of them will provide the pressure required.

    A bike like that should have a heap of opportunities to salvage current draw though, replace tail/park/indicators with LED's etc..etc..

  19. #19
    Member darkfibre's Avatar
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    I have 19 amps to play with, so I may end up regretting the dual headlight (or just use the one on low beam), also the sub woofer draws 10 amps just by itself
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    Just only give it shit during the day time

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