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1984 Honda Shadow Vt700c Cafe Racer

This is a discussion on 1984 Honda Shadow Vt700c Cafe Racer within the Project Builds forums, part of the Caferacer.net Forums category; Andddd I'm back. So put a few miles on it last year, I got a car so i haven't used the bike much this year. ...

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Thread: 1984 Honda Shadow Vt700c Cafe Racer

  1. #291
    Member Star Lord's Avatar
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    Andddd I'm back.
    So put a few miles on it last year, I got a car so i haven't used the bike much this year. But I want to get some riding in this fall. However having some fuel issues.

    Recap from last year:
    My fuel pump was over heating and shutting off and I could not figure out why!
    I bought another fuel cut off switch relay, and a new pump. Tried old pump new relay, new pump old relay, new pump new relay. Nothing worked.
    So I just ditched the pump and relay, and went gravity fed. Which worked fine. However being the genius that I am I removed the petcock and flooded my rear cylinder. Hooray.
    I drained it, changed the oil and reinstalled the petcock. And thats how I ended summer 2017.

    Where we are now:
    end of summer 2018.
    I cleaned the carbs, I have the floats set high high, so that the bowls can fill more. Fuel is still gravity fed.

    Problem:
    I believe the bike is starving for fuel because it dies a minute after riding (idles extensively) and starts back up after a few seconds of sitting. (The less time I wait before riding it on the quicker it dies, because i feel like the bowls aren't filling)
    Also the carb and tank are positioned awkwardly, as a result the less fuel is in the tank the less pressure I have in the line, this creates a jarring inconsistency.
    Current tank nozzle points away from carb.

    Thoughts:
    there has got to be some optimal fuel pressure (I imagine it is very little) where the bowls stay full but fuel doesnt blow past the needle and flood...

    Ideal scenario:
    Get the bike back up and running with fuel pump.

    Current ideas:
    Increase diameter of fuel hose, I feel like if I do this I'll lose pressure in the line faster as the tank drains but I'll have more volume at the ready.
    Decrease diameter of the line, would increase the pressure, and It would probably maintain the pressure closer to empty.
    Cut current tank nozzle off and weld new threaded bung for AN fitting potentially use one of those filtered petcocks and just have a one straight line from tank to carb. Creating less bottle necks and simplifying the journey the fuel has to make from tank to carb.

    Future ideas:
    I have taken thermodynamics I.
    Spring 2019 I'm taking thermo II, and computational fluids. I have already started thinking about how to make this bike fuel injected. If I could properly design the manifold, I pretty confident i could machine it. Prototyping the fittment would be easy as I have a large 3D printer. Last year or so I have put about 100hours each on cnc and lathe. I have experience with programming so working with air and fuel sensor won't be too difficult.
    Thinking about making this my senior design project. Not sure yet.
    Delson Da Silva,
    Mechanical Engineering, BS 2019
    Boston, Massachusetts
    My projects: www.projects.djd.im | [email protected]

  2. #292
    Senior Member Teazer's Avatar
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    Check you float valves. Carbs with fuel pumps typically have very small diamtere float valves in the 1.5mm range where bikes with gravity feed need much larger valves (2.5 - 3.5mm) to allow sufficient fuel to flow at lower pressure.
    Star Lord likes this.

  3. #293
    Senior Member XB33BSA's Avatar
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    you could not possibly be anything but a complete moron from another planet who is trolling us.
    fer fucks sake you don't even know basic physical principles of gravity and whatnot....that exist on this planet
    and you are an engineer ?? horseshit !! ,fuckoff ,go home and troll on your own planet asshole
    Last edited by XB33BSA; 09-17-2018 at 10:15 AM.

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  5. #294
    Senior Member TrialsRider's Avatar
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    I cleaned the carbs, I have the floats set high high, so that the bowls can fill more. Fuel is still gravity fed.
    ... that might not work so well, fuel level is set to make the venturi pipe do it's thing :|

    Problem:
    I believe the bike is starving for fuel because it dies a minute after riding (idles extensively) and starts back up after a few seconds of sitting. (The less time I wait before riding it on the quicker it dies, because i feel like the bowls aren't filling)
    Also the carb and tank are positioned awkwardly, as a result the less fuel is in the tank the less pressure I have in the line, this creates a jarring inconsistency.
    Current tank nozzle points away from carb.
    ... you just confirmed why the bike has a fuel pump on it.

    Thoughts:
    there has got to be some optimal fuel pressure (I imagine it is very little) where the bowls stay full but fuel doesnt blow past the needle and flood.
    ... is totally dependent on your fuel consumption,
    have you done anything to the bike to increase fuel consumption significantly like remove the entire exhaust system and or install pod filters

    Ideal scenario:
    Get the bike back up and running with fuel pump. <- yaaaa! that or replace the fuel tank with something far superior.

    Current ideas:
    Increase diameter of fuel hose, I feel like if I do this I'll lose pressure in the line faster as the tank drains but I'll have more volume at the ready.
    Decrease diameter of the line, would increase the pressure, and It would probably maintain the pressure closer to empty.
    Cut current tank nozzle off and weld new threaded bung for AN fitting potentially use one of those filtered petcocks and just have a one straight line from tank to carb. Creating less bottle necks and simplifying the journey the fuel has to make from tank to carb.
    .... Montesa 360VA had 2 fuel taps and 2 fuel hoses to feed one carb. ... needed both taps open on reserve or you could starve the 54mm Bing for fuel if you really, really worked at it.


    btw: your fuel pump is on there to deal with a problem that manifests when the tank is low on fuel, if the thing lacks fuel pressure when your tank is full you have a problem elsewhere.
    Last edited by TrialsRider; 09-17-2018 at 02:25 PM.

  6. #295
    Senior Member TrialsRider's Avatar
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    ... have you seen the ones with a secondary fuel tank that houses a fuel pump? The guys who designed that abortion were suppose to be engineers too!

  7. #296
    Member Star Lord's Avatar
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    Quote Originally Posted by TrialsRider View Post
    I cleaned the carbs, I have the floats set high high, so that the bowls can fill more. Fuel is still gravity fed.
    ... that might not work so well, fuel level is set to make the venturi pipe do it's thing :|

    Problem:
    I believe the bike is starving for fuel because it dies a minute after riding (idles extensively) and starts back up after a few seconds of sitting. (The less time I wait before riding it on the quicker it dies, because i feel like the bowls aren't filling)
    Also the carb and tank are positioned awkwardly, as a result the less fuel is in the tank the less pressure I have in the line, this creates a jarring inconsistency.
    Current tank nozzle points away from carb.
    ... you just confirmed why the bike has a fuel pump on it.

    Thoughts:
    there has got to be some optimal fuel pressure (I imagine it is very little) where the bowls stay full but fuel doesnt blow past the needle and flood.
    ... is totally dependent on your fuel consumption,
    have you done anything to the bike to increase fuel consumption significantly like remove the entire exhaust system and or install pod filters

    Ideal scenario:
    Get the bike back up and running with fuel pump. <- yaaaa! that or replace the fuel tank with something far superior.

    Current ideas:
    Increase diameter of fuel hose, I feel like if I do this I'll lose pressure in the line faster as the tank drains but I'll have more volume at the ready.
    Decrease diameter of the line, would increase the pressure, and It would probably maintain the pressure closer to empty.
    Cut current tank nozzle off and weld new threaded bung for AN fitting potentially use one of those filtered petcocks and just have a one straight line from tank to carb. Creating less bottle necks and simplifying the journey the fuel has to make from tank to carb.
    .... Montesa 360VA had 2 fuel taps and 2 fuel hoses to feed one carb. ... needed both taps open on reserve or you could starve the 54mm Bing for fuel if you really, really worked at it.

    btw: your fuel pump is on there to deal with a problem that manifests when the tank is low on fuel, if the thing lacks fuel pressure when your tank is full you have a problem elsewhere.
    I will set the floats back to stock height. This will hopefully tell me if its a fuel pressure or float level problem.
    I will take another shot at investigating why my fuel pump was overheating and shutting off. This is the only way I see to address the pressure issue, as per your comment.
    Are there "self regulating" fuel pumps and stop and go depending on the pressure?
    The one I have seems to run constantly unless fuel safety relay cuts it off. This is why I think it overheats, and shuts off

    When you say "replace the fuel tank with something far superior." what do you suggest?

    That Montesa 360VA is a pretty cool bike, quite the guzzler.
    Delson Da Silva,
    Mechanical Engineering, BS 2019
    Boston, Massachusetts
    My projects: www.projects.djd.im | [email protected]

  8. #297
    Member Star Lord's Avatar
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    Quote Originally Posted by Teazer View Post
    Check you float valves. Carbs with fuel pumps typically have very small diamtere float valves in the 1.5mm range where bikes with gravity feed need much larger valves (2.5 - 3.5mm) to allow sufficient fuel to flow at lower pressure.


    Good point I'll look into it.
    Delson Da Silva,
    Mechanical Engineering, BS 2019
    Boston, Massachusetts
    My projects: www.projects.djd.im | [email protected]

  9. #298
    Senior Member kenessex's Avatar
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    Set your carbs back to the stock fuel levels and fix your fuel pump issues. You still suck at diagnosing. I am pretty sure that your fuel pump has a set of contact points located in the base under a plastic cover. The cover collects moisture and corrodes the points set so they won't move. If the points stay closed, the pump runs continuously and overheats. Check your fuel pump.

    You can't get a carburetted bike with a fuel pump to run correctly and you think you can successfully get it to run with EFI?
    woodsman likes this.
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  10. #299
    Senior Member TrialsRider's Avatar
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    Quote Originally Posted by Star Lord View Post
    ... That Montesa 360VA is a pretty cool bike, quite the guzzler.
    Yep, fuel tank holds 2 gallons of premix and if you are careful that's just enough to finish a 20 minute moto race.

    What makes a good fuel tank imho: Aluminum construction because it is light weight and does not rust, capacity that is commensurate with your application, location and shape that facilitates gravity feed if you are running carburetors, and lastly it should look really fly on the bike.

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