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DaveM

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Fuel pump
« on: January 14, 2010, 04:38:44 PM »
 670 Rotax, twin 44 Mikuni's,  in a buggy. If the tank is above the engine, do I still need to, or should I,  run the stock pulse type fuel pump?
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Offline fabr

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Re: Fuel pump
« Reply #1 on: January 14, 2010, 07:24:13 PM »
It should gravity feed just fine unless the inlet needle is spring loaded due to the use of a fuel pump in the original application.
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SPEC

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Re: Fuel pump
« Reply #2 on: January 15, 2010, 05:00:59 AM »
Sled motor...
Yup you need the pump
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Offline fabr

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Re: Fuel pump
« Reply #3 on: January 15, 2010, 05:48:01 AM »
because of????????
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"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

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 " You have all the right in the world to believe any damn thing you'd like, but you don't have the right to demand that I agree with your fantasy"

SPEC

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Re: Fuel pump
« Reply #4 on: January 15, 2010, 06:04:44 AM »
Carbs are meant to run with a pump on the sled,
Sled carbs are slightly different in the inlet needle and seat area than conventional bike gravity fed carbs
Plus the pump makes sure the carb bowls are full of fuel at all times even WFO since the pump runs off of the pulses from the motor
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Offline fabr

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Re: Fuel pump
« Reply #5 on: January 15, 2010, 06:31:23 AM »
What's different in the needle/seat area?
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"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

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 " You have all the right in the world to believe any damn thing you'd like, but you don't have the right to demand that I agree with your fantasy"

SPEC

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Re: Fuel pump
« Reply #6 on: January 15, 2010, 08:27:04 AM »
I'll have to get you some pix
But If you use bike carbs on a sled motor they need to have the needle and seats replaced with the parts for use with a pump...I have never had any luck with gravity feed keeping up with thirsty sled motors
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Offline fabr

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Re: Fuel pump
« Reply #7 on: January 15, 2010, 09:52:26 AM »
That makes sense.
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"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
 " You have all the right in the world to believe any damn thing you'd like, but you don't have the right to demand that I agree with your fantasy"

SPEC

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Re: Fuel pump
« Reply #8 on: January 15, 2010, 01:23:54 PM »
And the fuel inlet too eyes
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Offline Nutz4sand

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Re: Fuel pump
« Reply #9 on: January 15, 2010, 01:44:19 PM »
Needle and seat size can be a big factor. Systems designed for fuel pumps can have smaller holes and different tapers to the needles and seats. Since they have pressure to force the fuel through.

But so can the layout. If the fuel tank is level with or below the carbs then its a no brainer. It needs a fuel pump.

If your machine is gravity feed with a higher tank and the tank is BEHIND the motor on heavy acceleration (ESPECIALLY UP a hill) makes the fuel in the lines (due to the fuels weight) be held back from flowing towards the carbs.

If the tank is ahead of the motor with the lines heading backwards to the carbs the fuels weight will actually induce flow towards the carbs on hard acceleration. The place fuel comes out of the tank also affects this.

A well designed system can even use larger fuel lines (properly laid out) to increase this pressure and helop keep the carbs filled on accelleration and up hills under load.



 
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Offline fabr

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Re: Fuel pump
« Reply #10 on: January 15, 2010, 02:11:46 PM »
Quote from: DaveM on January 14, 2010, 04:38:44 PM
670 Rotax, twin 44 Mikuni's,  in a buggy. If the tank is above the engine, do I still need to, or should I,  run the stock pulse type fuel pump?
As to this SPECIFIC question I'm inclined to say the answer is no you likely wouldn't HAVE to have the pump but IMO it would be wise to do so anyway.
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"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
 " You have all the right in the world to believe any damn thing you'd like, but you don't have the right to demand that I agree with your fantasy"

DaveM

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Re: Fuel pump
« Reply #11 on: January 16, 2010, 07:41:06 AM »
Quote from: masterfabr on January 15, 2010, 02:11:46 PM
As to this SPECIFIC question I'm inclined to say the answer is no you likely wouldn't HAVE to have the pump but IMO it would be wise to do so anyway.

 That's my thinking as well.

I did a test yesterday. I'm re-engineering this install and currently there is no tank. I put 6 " of 1/4" fuel line on the carbs, filled the carb bowls with a squeeze bottle. The flow stopped good on both carbs once full which left about 2" of visible fuel in the lines. Fired it up and as it ran the fuel disappeared from the lines into the bowls. So I surmise that they needle and seat set-up is not sprung to require a pump. But I have the pump, it's an easy install, so I might as well use it.
 On a side note, I gave the thing a squirt up and down the driveway, (in between filling the float bowls with the squeeze bottle eyes), spun the tires on pavement all the way. Maybe too much motor for trail riding. Got to look at some options for a different powerplant.
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Offline Engineer

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Re: Fuel pump
« Reply #12 on: January 17, 2010, 10:36:09 AM »
Quote from: DaveM on January 16, 2010, 07:41:06 AM
That's my thinking as well.

I did a test yesterday. I'm re-engineering this install and currently there is no tank. I put 6 " of 1/4" fuel line on the carbs, filled the carb bowls with a squeeze bottle. The flow stopped good on both carbs once full which left about 2" of visible fuel in the lines. Fired it up and as it ran the fuel disappeared from the lines into the bowls. So I surmise that they needle and seat set-up is not sprung to require a pump. But I have the pump, it's an easy install, so I might as well use it.
 On a side note, I gave the thing a squirt up and down the driveway, (in between filling the float bowls with the squeeze bottle eyes), spun the tires on pavement all the way. Maybe too much motor for trail riding. Got to look at some options for a different powerplant.

To much power??  ;D


Pics please!
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DaveM

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Re: Fuel pump
« Reply #13 on: January 17, 2010, 04:46:49 PM »
Don't laugh now, I'm just getting started with it. Lot to do. :-[


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