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Thread: Fuel Injection?

  1. #1
    BigDaddyPT's Avatar
    Join Date
    Oct 2006

    Fuel Injection?

    Hey...what do you guys know about this system?

    I'm getting an

  2. #2
    SeaLion's Avatar
    Join Date
    Aug 2006
    Ride Mohave To Havasu. Live In Los Angeles.
    Man those retailed for around $1300 in 1995 dollars. Supposed to work well once set up. People either loved them or hated them. I guess the ones that got it dialed in are the ones that loved it.

  3. #3
    Moderator beerdart's Avatar
    Join Date
    Aug 2006

    Carb Tuning GroupK 1999

    From groupK
    Mechanical Fuel Injection - Within the pwc community, the only aftermarket fuel injection system that has stood the test of time is the one offered by MRD. This mechanical injection system has an advantage over all carburetors in the sense that it does not depend on "carb signal" to conduct itís metering work. Hence, MRD owners can use huge venturi throat diameters with little concern of harming "single point" metering. Single point metering refers to the amount of fuel being delivered at one particular load level, and one particular rpm. The MRD fuel delivery curve is strictly rpm based (driven by a fuel pump at the crankshaft), and allows the owner to make various range adjustments via a series of adjuster screws and pop off valves. Many pwc owners (grudge racers in particular) have had very good peak speed results with this fuel management system on many different engine platforms.
    Unfortunately, all this simplicity comes with a few important compromises. The first, and foremost, is that the MRD system has absolutely no ability to deliver less fuel to an unloaded (out of the water) engine that is offering a weaker signal. The result of this inability to self-adjust (as all conventional carbs do) is a very noticeable over-rich condition when operated on rough water conditions. This same phenomenon contributes to the MRD's very high rate of total fuel consumption (higher than virtually any conventional design carburetor). On the water, this inability to correct fuel metering for unloaded operation can lead to a "landing with the brakes on" feeling as you run through rough water with high throttle openings. MRD owners, who ride on rough water, are forced to make a compromise of the mixture that might be ideal on glass vs a mixture that does not foul the plugs during unloaded operation. With such a compromise setting, the risk of detonation, or piston scoring, is greatly increased if you suddenly find a big piece of glass water. Furthermore, mechanical fuel injection will not correct for varying air density conditions (as a strong signal carburetor can).
    All this said, the MRD system can work well so long as you are willing to regularly fine tune it for any changes in the prevailing water and weather conditions that you will be riding in. While the MRD system has little in the way of self compensating abilities for mid range operation, it "can" be easily tuned to meter the correct amount of mixture for full throttle smooth water operation (this is called "single point" operation). Because of itís ability to work very well under single point operation, the MRD systems have been successfully used by many grudge racers who ride only on smooth water conditions (where no compensating abilities are ever required).
    From our perspective, this system can work well for individuals that operate on glass water conditions in areas that do not experience significant swings in air temperature or air density. While this might be fine for some owners, most of the high performance pwc owners we deal with are seeking a fuel management system that is more versatile, and more forgiving to adjustment.
    About Atomizer Designs - Among the biggest design differences between all the aftermarket carburetors is the apparatus used to introduce the fuel into the passing air stream. These devices are called atomizers because their main function is to introduce the fuel into the air column as an "atomized" spray.
    By far the most common atomizer design is the "booster venturi" design (used in most production pwc carbs). Many folks (us included) have referred to the booster venturi as a "bomb-sight" atomizer because it has the appearance of a gunnerís bombsight.
    The booster venturi gets its name from the circular bell-mouthed venturi mounted at the top of a main jet fuel outlet. This venturi helps to boost the negative pressure signal over the main jet supply orifice (hence the term booster venturi). We have been reminded, by the carburetor folks, that nothing inside any carburetor is being "bombed", so they would really prefer that we use the technically correct term, booster venturi...fair enough.
    Another popular design is the "atomizer tube" which is a brass bar that replaces the traditional booster venturi. There are variations in the shape and fuel outlet orifices among different aftermarket atomizer tube designs, however the basic concept of all these variations is the same. The atomizer bar represents a much smaller obstruction to airflow than the traditional booster venturi. Unfortunately the atomizer bar design does not have any additional device to induce strong signal directly over the high-speed orifice outlet (as the booster venturi has). One other design that has experienced intermittent popularity among pwc competitors is the "annular discharge" atomizer. These carbs introduce fuel (for the main jet) via a series of orifices around the full diameter of the carb throat. The intent of this design is to offer better performance than other designs because of superior fuel atomization abilities.

    Thanks To GroupK
    Attached Files Attached Files

  4. #4
    It looks like a cool pain in the ass that I'm going to pass on! Z

  5. #5
    jcc011185's Avatar
    Join Date
    Sep 2006
    Kannapolis NC (north of Charlotte)
    Lol yeah.. I love my car's fuel injection, but I didn't have to dial that in; and it's computer controlled... but I can't even imagine how hard it would be to get a mechanical one tuned properly... Hell, i can't even get carbs right...I'm having to "have them done" lol...


  6. #6
    SeaLion's Avatar
    Join Date
    Aug 2006
    Ride Mohave To Havasu. Live In Los Angeles.
    Like I said, for those that got them to work they worked well and those that couldn't or wouldn't spend the time, they were a nightmare. I would pass too. Too much effort for a rec set up.

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