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Thread: Dual Carb setup for the 084

  1. #1
    Administrator Papee's Avatar
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    Dual Carb setup for the 084

    First a little background on the carbs. They are Tillotson carbs made for the Army mule. The carbs were used on a twin cyl engine much like the 084. These twin cyls are a 42 cubic inch motor which is exactly half of the 084. The good thing about these crabs is that they are made to be on a motor with varying rpms which the carbs on a 084 are not, they are designed to run at a constant 3600 rpms.

    These carbs also have air and fuel adjustments as well as a accelerator pump making it a good choice for these motors if run as a dual setup.
    The carbs.


    The animal they are designed for, the Mule.



    I had some time to spend in the shop today but I didn't get much accomplished other than some head scratching. I am making or trying to make new intakes to allow these carbs to be used on our 084s. I didn't want to just build a box plenum because they are just not efficient and do not flow well. If you have any corners the gas will get trapped there and not flow well. I am trying to design intakes that will get the best performance from these carbs using round tube.

    The problem I am having is becasue of the magneto position it is hard to get the right placement on the carbs. After looking at if for some time I see that I have two choices. One would be to raise the intake tubes so the carb on the mag side has room above the mag, this would require that I also raise the other side to match to make both intake sides the same. The other is to scrape the "use the stock intake tubes" idea and make a new set of intakes that would bring the carbs to the outside of the engine right above where the intake tubes come out of the cylinders.

    Like this



    The problem with this is that it would be a nightmare to figure out a reliable throttle linkage. I'm now trying to figure out a way to stack them. There are other ways to do it also by making a plenum in the end of the stock intake to accept the two carbs but this just would not be efficient.

    Any ideas would be appreciated.
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  2. #2
    Member aerokirk's Avatar
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    Re: Dual Carb setup for the 084

    Can you post more pictures of the carbs, specifically the intake flange ends and throttle linkages? I agree, the ideal configuration would be side by side or stacked so a solid linkeage rod could be connected to the throttle actuators.
    11'6" Marty Bray Hull
    4A084 Continental
    Circle "S" 1.69:1 Reducer
    67" Whirlwind Razor X Prop
    SS Rigging

  3. #3
    Administrator Papee's Avatar
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    Re: Dual Carb setup for the 084

    I'll get more pics later but it's pretty much like the stock carb as far as the flange and linkage. The flange is just a tad smaller bolt spacing than the stock carb.
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  4. #4
    Member aerokirk's Avatar
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    Re: Dual Carb setup for the 084

    Papee ... I checked out the Saturn Surplus website and I don't see the carbs listed. Do they plan on carrying them or are they just a one-time purchase? I was trying to see a cost but if they're from an M274 mule I don't see a listing for them
    11'6" Marty Bray Hull
    4A084 Continental
    Circle "S" 1.69:1 Reducer
    67" Whirlwind Razor X Prop
    SS Rigging

  5. #5
    Administrator Papee's Avatar
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    Re: Dual Carb setup for the 084

    He doesn't have them listed. I can get you a price if you want. If this all works out I will most likely offer it as a kit with the carbs included.
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  6. #6
    Junior Member Doozit20's Avatar
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    Re: Dual Carb setup for the 084

    My throttle is run by a cable in a sleeve much like a bike break cable. I think that you can look up a dual mikuni cable from a rotax engine. It should be fairly easy to figure a way to utilize those for your dual setup as long as the carbs are close enough together as to not kink the cable. Now being able to sincranize the two carbs will be the biggest challenge with that setup though it has been done and I have confidence that you can figure something out
    Hull:10'6"x69" 1/2 deckover .100
    Motor:4a084 w/ stock carb
    Reduction:direct drive
    Prop:ultraprop 3 blade 59x10*
    Mods:Motorcycle exhaust

  7. #7
    Administrator Papee's Avatar
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    Re: Dual Carb setup for the 084

    I have no problem figuring out the linkage once I get the intake made, I already have that part solved. I use to run a Honda 750 four back in my younger days(4 carbs) so I'll have no problem setting them up. It's just a brain teaser to get the intakes figured out. I guess there is no easy way to do it and I'll just have to make the intake tubes from scratch. I was hoping that I could use the stock intake tubes to make it a quicker conversion.
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  8. #8
    Administrator Papee's Avatar
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    Re: Dual Carb setup for the 084

    Here's more photos.
    Attached Images Attached Images    
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  9. #9
    Junior Member Doozit20's Avatar
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    Re: Dual Carb setup for the 084

    4 carbs wow that would be crazy. I think the only way would be to make up different short tubes going straight into the heads. I looked up the EFI that a guy did a few years back and the results were very impressive. I think the guy named Les?? was able to get a wood prop 58x25* to 3100 direct drive with his setup but I dont think that was cheap in my aspect. Keep us updated on what you come up with..if anyone can figure it out I know you can
    Hull:10'6"x69" 1/2 deckover .100
    Motor:4a084 w/ stock carb
    Reduction:direct drive
    Prop:ultraprop 3 blade 59x10*
    Mods:Motorcycle exhaust

  10. #10
    Member aerokirk's Avatar
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    Re: Dual Carb setup for the 084

    Papee ... Though you may not be using a Circle S reduction drive on your boat build, for those of us who are, I just saw something on mine that you should be aware of in your design of the dual carb setup if you are planning to market it in the future. The starter protrudes forward from the reducer drive just above the intake tubes on the mag side of the engine. From the top of the intake tube to the top of the starter is 5 1/2" and it extends forward to just behind the back of the mag. I just painted my engine today and attached the reducer and starter for the first time and I realized that a redesigned intake manifold would have to be kept low on the mag side if it were to work with this engine. I am attaching some pics to show the relative locations. (I painted my engine gloss black so its hard to see in the pics... sorry!) Just thought you should know
    Attached Images Attached Images      
    11'6" Marty Bray Hull
    4A084 Continental
    Circle "S" 1.69:1 Reducer
    67" Whirlwind Razor X Prop
    SS Rigging

  11. #11
    Administrator Papee's Avatar
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    Re: Dual Carb setup for the 084

    Thanks for the photos of the redrive. I think the best way to do it is make the intakes from scratch and position the carbs at about the same place the stock ones are but higher to clear the magneto.
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  12. #12
    Junior Member Doozit20's Avatar
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    Re: Dual Carb setup for the 084

    I actually thought about moving the intake tubes up and forward for my dads boat if the starter didnt clear the block. The plan would have been to have the same length tubes but up and forward as you are planning papee so the starter could be mounted on top of the engine but we manages to squeeze it where it is at now so no worries. If we find it is getting too much heat where its at then thatll be the route we will go but until we know for sure the starter will stay where we have it at now.

    Keep us posted on those duals papee
    steve
    Hull:10'6"x69" 1/2 deckover .100
    Motor:4a084 w/ stock carb
    Reduction:direct drive
    Prop:ultraprop 3 blade 59x10*
    Mods:Motorcycle exhaust

  13. #13
    Administrator Papee's Avatar
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    Re: Dual Carb setup for the 084

    I will and please do a build thread on your starter setup. I most likely will be doing about the same thing to mine and my uncles boat.
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  14. #14
    Junior Member Doozit20's Avatar
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    Re: Dual Carb setup for the 084

    Ok ill see what I can throw together
    Hull:10'6"x69" 1/2 deckover .100
    Motor:4a084 w/ stock carb
    Reduction:direct drive
    Prop:ultraprop 3 blade 59x10*
    Mods:Motorcycle exhaust

  15. #15
    Member aerokirk's Avatar
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    Re: Dual Carb setup for the 084

    Papee ... any progress on the dual carb setup?
    11'6" Marty Bray Hull
    4A084 Continental
    Circle "S" 1.69:1 Reducer
    67" Whirlwind Razor X Prop
    SS Rigging

  16. #16
    Administrator Papee's Avatar
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    Re: Dual Carb setup for the 084

    Nothing much but I do have a plan now. I've been full on working on finishing my uncles boat. I got the bottom paint and just waiting on god weather to get it on.
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  17. #17
    Administrator Papee's Avatar
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    Re: Dual Carb setup for the 084

    I've been working on this setup some and have a question for the reduction guys. If the spider part of the intake were reversed so it were pointing toward the prop would there be a clearance problem for you guys? I would only need 1 1/2 inch past the flange where the carb mounts. My design really does not go past the plane of the motor if you would put a straight edge verticle on the prop end of the motor. My design points the carbs back towards the original direction they are in now and would be located at about the center of the motor. I'll try to draw something up if this is too hard to understand.
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