Fuel pump absolutely necessary on a 1985 VF700?

Discussion in '1st & 2nd Generation 1983-1989' started by FasYankee, Mar 17, 2014.

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  1. FasYankee

    FasYankee New Member

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    Wondering if the fuel pump is absolutely necessary on a 1985 VF700. Bike build would be easier if I could forgo the pump. Never had a carb'd bike with a pump before....always just gravity fed.
     
    FasYankee, Mar 17, 2014
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  2. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    It's well accepted that the 500 runs well without the pump. Even Honda did away with it on the 500 in '86 I believe.

    As for the 700, 750, and 1000; the topic is hotly debated. At low fuel levels the fuel flow to the bowls can be insufficient. There's 4 carbs there and the petcock is at the same level as the carb fuel rails. So there's very little help coming from gravity when the fuel level gets low.

    I usually subscribe to the idea that manufacturers would rather not include unnecessary things that would drive their costs up.
     
    tinkerinWstuff, Mar 17, 2014
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  3. Jeff_n_Franklin_Tn

    Jeff_n_Franklin_Tn New Member

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    Yes, Honda did do away with the fuel pump on the 86 500F's BUT they also put a larger fuel petcock and a larger fuel supply line to the carbs. The 84/85 model 500F's will run fine without a pump but I think you'll have fuel starvation issues at wide open throttle....maybe not. :)
    Jeff
     
    Jeff_n_Franklin_Tn, Mar 17, 2014
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  4. squirrelman

    squirrelman Member

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    Without pump you won't be able to use bottom 1/3 of tank.
     
    squirrelman, Mar 17, 2014
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  5. TOE CUTTER

    TOE CUTTER Mullet Man

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    Squirrel is on the money.
     
    TOE CUTTER, Mar 18, 2014
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  6. Jeff_n_Franklin_Tn

    Jeff_n_Franklin_Tn New Member

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    Why not? Considering the fuel tank is above the carbs.
     
    Jeff_n_Franklin_Tn, Mar 18, 2014
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  7. TOE CUTTER

    TOE CUTTER Mullet Man

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    When the fuel level gets near the petcock it will stop gravity feeding and needs to be pulled oot.
     
    TOE CUTTER, Mar 18, 2014
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  8. Jeff_n_Franklin_Tn

    Jeff_n_Franklin_Tn New Member

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    I'm assuming this is with the fuel pump connected? If the fuel pump was bypassed that would alleviate the problem ???
     
    Jeff_n_Franklin_Tn, Mar 18, 2014
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  9. TOE CUTTER

    TOE CUTTER Mullet Man

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    I you ever try to empty the tank on gen 1 or 2 you have to pump oot the last couple of gallons or turn the tank upside down because of the internal plumbing in the tank because of the petcock design. Never had to do it on gen 1 but have on gen 2, it will sputter and run oot of gas at aboot half a tank.
     
    TOE CUTTER, Mar 18, 2014
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  10. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    I thought I explained it in the first post. Guess I have to get clearer.
     
    tinkerinWstuff, Mar 18, 2014
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  11. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    Maybe this covers it
    [video=youtube_share;ggNTFZktgVs]http://youtu.be/ggNTFZktgVs[/video]
     
    tinkerinWstuff, Mar 18, 2014
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  12. BWeiss

    BWeiss Johnny Partseed

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    look at tink getting all engineery and shit...Honestly, I was probably going to post something on Bernoulli's equation but you beat me to it.
     
    BWeiss, Mar 18, 2014
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  13. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    the voice in this video is easier to listen to

    [video=youtube_share;N4awnV1YLsU]http://youtu.be/N4awnV1YLsU[/video]
     
    tinkerinWstuff, Mar 18, 2014
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  14. BWeiss

    BWeiss Johnny Partseed

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    Better than my chinese instructor when I took the "fruids" class...
     
    BWeiss, Mar 18, 2014
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  15. Jeff_n_Franklin_Tn

    Jeff_n_Franklin_Tn New Member

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    You all have heard of Jamie Daugherty from Daugherty Motorsports? He used to race these old bikes. It's possible he still does. This is a quote from him from a question I posted on another forum and a PM to him.

    "No problem at all-the fuel will run completely out of the tank.
    I think what happens is people have a problem -> they look for the source -> find that only 2/3 comes out of the tank. Therefore, you need a pump to get the remaining 1/3 out, right? They forget the first step: they had a problem. Normally this problem is the fuel petcock which is the reason the last 1/3 doesn't come out right away(it will eventually, by the way). A fuel pump just masks the real issue.
    All my V4's run gravity feed and I run the tank completely dry without any difficulty. I hope this helps!"
     
    Jeff_n_Franklin_Tn, Mar 18, 2014
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  16. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    If I'm not mistaken, JD is in Ohio which ranges 450-1500 ft above sea level. It's one of the flattest states in the country. Try the same thing at 5000ft above sea level or more while a low pressure front is moving in and see what happens. There is less atmospheric pressure which will make the fuel flow slower.

    Again, my feeling is, when your most enthusiastic customers are young males with little money, you don't make the product cost more by adding unnecessary gadgets.
     
    tinkerinWstuff, Mar 18, 2014
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  17. Jeff_n_Franklin_Tn

    Jeff_n_Franklin_Tn New Member

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    Jamie is in Fort Wayne, Ind. Elevation-791 feet above sea level. The atmospheric pressure between Fort Wayne, Ind and Denver, Co. is 2 psi. That's really not that much of an effect of your flow rate in Denver, Co.
    http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html
    All I'm saying is I heard of many people that do run these old bikes without fuel pumps and without issues. If the atmospheric pressure has that much of effect on gravity fed motorcycles in Colorado then all motorcycle manufactures would have had to develop special fuel systems to deal with that problem for you fine motorcyclists in Denver, Co. Gravity is the key word here. Gravity is the same in Denver, Co. as it is in Fort Wayne, Ind. Gasoline in Denver, Co. weighs the same as gasoline in Fort Wayne, Ind.
    Not trying to be a jack ass about this. I just think you should consider that you might have a blockage in your tank or petcock. It does happen.
     
    Jeff_n_Franklin_Tn, Mar 18, 2014
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  18. tinkerinWstuff

    tinkerinWstuff Administrator Staff Member

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    2 doesn't sound like a big number until you consider it's PSI

    They didn't have to engineer different systems for different locations and conditions. Just one bulletproof system that would work in all conditions; i.e. a fuel pump on models that needed it.

    I90 Max elevation 6,300ft
    I80 Max elevation 8,600ft
    I70 Max elevation 11,100ft
    I40 Max elevation 7,300ft
     
    Last edited: Mar 18, 2014
    tinkerinWstuff, Mar 18, 2014
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  19. Jeff_n_Franklin_Tn

    Jeff_n_Franklin_Tn New Member

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    But the fuel tank will build up a little pressure from the fuel itself sloshing around and from the sunlight heating up the tank. More than atmospheric pressure...otherwise it couldn't vent through the cap.
     
    Jeff_n_Franklin_Tn, Mar 19, 2014
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  20. TOE CUTTER

    TOE CUTTER Mullet Man

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    You can just remove the pump and plan on always having half a tank of unused gas. :wacko:
     
    TOE CUTTER, Mar 19, 2014
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