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Hello all, I am new to the scoot world and learning quickly.
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Post by mrscoot on Jul 18, 2014 17:17:15 GMT -5
I hear talk about fuel pumps and I just don't get it,,, Maybe I had something different,,, I don't know.... I ride mostly open hilly highway 50-60 mph with my scoot. A few months ago shortly after I got my scooter I noticed at WOT cruising down the highway I would loose fuel to the carburetor after just a mile or so. I determined that it was the fuel pump going out so I replaced it with a new one. The trouble continued! I was a little confused at this time because I had never seen a vacuum operated fuel pump before. I have been a custom hotrod car builder and antique automotive restorations guy all my life. A vacuum operated fuel pump? I just had to find out more about this so I took my old "pump" and carefully opened it up. Just as I had suspected, it is not a pump at all! It is only a vacuum operated fuel valve!!! Here is the deal,,, at WOT, intake manifold vacuum drops to less than 1hg vacuum,,,at this point the carburetor is operating in much the same way as grandmothers perfume spray bottle,,, Airflow and not vacuum. 1hg. at the manifold is not nearly enough to keep a fuel valve open or any vacuum operated device operational for that matter (Remember grandpa's old Nash Rambler had vacuum operated windshield wipers and whenever he got on the gas pedal the wipers would stop,,, No vacuum!!!). Of course the valve would close shutting off the fuel supply and fuel starvation happens. This would not be noticeable in city and or bellow WOT. Out on the open highway at 50-60mph on a 10-20 mile ride and you have problems. My solution the what I was experiencing was just a standard lever action fuel petcock valve and loose the vacuum operated valve altogether.
I now get out on the open road and run WOT 50-60mph constant mile after mile trouble free and have been doing so for many hundreds of miles. |
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Fuel Pump????
by: geh3333 - Jul 18, 2014 18:41:51 GMT -5
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Post by geh3333 on Jul 18, 2014 18:41:51 GMT -5
Your right about the fuel " valve " it's not a pump at all . I took mine out " they're junk" and installed a 1/4 inch shutoff valve . Some hVe fuel tanks that sit below the carb and need a fuel pump and many have tanks that sit up high and just work off gravity like ours . It kinda bothers me when they are called fuel pumps and all they are are just a vacuum operated valve .
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Post by william42 on Jul 18, 2014 19:12:13 GMT -5
Well I have one of those Vacuum Operated Fuel Valves on my Scoot because my gas tank is way lower than my carb. After trial and error I'm convinced that I cannot go WOT for more than a few seconds or my float bowl will run dry. My need for speed is no longer an issue any more with my advanced age. I just want to get where I'm going doing the speed limit of 45mph and she does that just fine. I've learned to use the downhill slopes to gain momentum to make it up the next hill without the need for WOT. And against a strong headwind fighting my large windshield, I just don't get up to speed quite as quickly. Besides, there isn't much more left after about half throttle anyway so WOT just doesn't matter. I just had to learn how to drive it. All is well.  |
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Fuel Pump????
by: geh3333 - Jul 18, 2014 19:53:41 GMT -5
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Post by geh3333 on Jul 18, 2014 19:53:41 GMT -5
Have u ever tried adjusting the float in the carb ?
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New Rider
Currently Offline
Hello all, I am new to the scoot world and learning quickly.
Posts: 16
Likes: 4
Joined: Jun 17, 2014 12:52:27 GMT -5
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Post by mrscoot on Jul 18, 2014 23:05:54 GMT -5
yes, it's been running awesome since I removed the vacuum valve and replaced it with a regular fuel valve!!!
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Fuel Pump????
by: geh3333 - Jul 19, 2014 2:16:38 GMT -5
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Post by geh3333 on Jul 19, 2014 2:16:38 GMT -5
Sorry mrscoot , I was asking william42 about the float . Lol . But that's good to know , those vacuum valves suck .
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Post by rockynv on Jul 19, 2014 4:33:39 GMT -5
There are two different items used on a scooter depending on the location of the tank. If the fuel tank is mounted above the carburetor it could have either a vacuum operated fuel pump or petcock while with the tank mounted below the carburetor it will usually be a vacuum operated fuel pump. Vacuum operated fuel pumps work due to the intake pulse between the throttle plates and the intake valve so it is critical that the vacuum line they are connected to is on the intake manifold and not part of the carburetor. At high speed with wide open throttle there will not be enough engine vacuum to keep a vacuum petcock open and the intake pulse can become so low that it can stop a dirty or marginal quality vacuum pump from working,
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Post by william42 on Jul 19, 2014 4:38:02 GMT -5
I looked at it some time ago, when I first found out about "the issue" but I figured that I best leave well enough alone for I'd have messed it up if I adjusted it. I thought about installing a higher output "pump" but again, I can get along with it by just adjusting my driving habits. It aint no big deal.
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Post by scooter on Jul 20, 2014 18:37:03 GMT -5
Mine is an actual pump. My tank is below the carb. I cleaned the carb and put it back on, and forgot to put the fuel line back on and, sure enough, 'spurt spurt spurt', out came the fuel with every rotation.
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Post by alleyoop on Jul 20, 2014 18:53:32 GMT -5
Its amazing what you hear, all the 250+ scoots with the tank up in front just like mine require a Vacuum Operated Fuel Pump and you can ride at 60+ with no problems whatsoever. Now on some the Fuel Pump may have been mounted higher than the tanks outlet which can create a problem. Reason is now in order for the gas to get to the pump so it can pump fuel to the carb, the amount of gas in the tank to have enough push to fill the hose and move the gas up to the carb may not be enough and now you have a dry pump. Here you want the fuel pump at least close to even with the outlet from the tank or little lower so that pump always has gas to pump.
With the tanks behind the seat which are gravity feed systems, folks have the hoses going up and down and to long and liquid does not flow up very well unless something behind it is pushing it. So in this situation you straighten out the fuel hose all the way from the tank to the petcock and fuel filter and down to the carb.
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..BAD TO THE BONE..