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Discussion Starter · #1 ·
Dear all,

I checked the flow rate of my 1977 GL1000 fuel pump at 3000 revs and it's pumping 700ml per min. The spec is supposed to be 450ml. Has anyone heard of a pump over supplying?

By the way, can anyone tell me how the carbs deal with the excess fuel required as there is no return?

Many thanks


Mark
 

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That's not "overpressure".... that's just "more than adequate supply" you measured. :)
Pressure is a totally different measure. Excessive pressure will overwhelm inlet needle and seats and cause flooding if it's high enough, a "more than adequate supply" measured under zero back pressure will not.


Dear all,

I checked the flow rate of my 1977 GL1000 fuel pump at 3000 revs and it's pumping 700ml per min. The spec is supposed to be 450ml. Has anyone heard of a pump over supplying?

By the way, can anyone tell me how the carbs deal with the excess fuel required as there is no return?

Many thanks


Mark
 

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You have informed us of the volume, but what is the pressure
 

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Discussion Starter · #6 ·
Hi there,

Thanks for replies

I don't have a pressure gauge, all I can do is measure the volume of flow, which is a function of pressure.

How do the carbs deal with all th eexcess fuel please?

Ride safe

Mark
 

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There are several ways to limit a pump's pressure capability inside the pump itself, depending on design. Some pumps are a set of vanes driven by electric motor, some are a simple plunger between wire wound poles that act as electro magnets and a set of points that open and shut at stroke end, a spring or pressure feed back returning the plunger for next stroke, and some are "mechanical" and usually use lever operated diaphrams.
Up to the point that the limit is reached, the pump will pump fuel at a given flow rate dependent upon volume of each stroke or revolution of pumping mechanism.
Once the pressure limit is reached, it can no longer pump, and fuel stops moving until the pressure above the pump drops (through use).

Gravity feeds depend on weight of fuel above the float bowl in a tank and lines. They loose pressure with use as weight of fuel above float bowl is less when empty than full (Model T Fords and my old push mower come to mind).
Early racers used hand operated pumps to pressurize fuel tanks (MOON comes to mind) to maintain fuel flow, they had a pressure release that limited pressure.
 

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Here is how I explain fluid movement.
"pressure is the measurement of resistance to flow"
 

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The mechanical pumps on these bikes is adequate but not going to put out excessive pressure. Normally the volume/time called for in the manual is a minimum value. What your pump is telling you is that the pump, fuel lines, fuel filter and tank screen are in good condition.
 

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to look at it another way.
If the bike had a fuel tank above the carb and used only gravity to feed the engine,
you would have the same pressure at the carb if you had 3/8 fuel line or a 2" fuel line but the 2 inch line would have way more flow if you let it run into a container for 30 seconds compared to the 3/8 inch line.
But hooked up to the carb it would not notice any difference.
Wilf
 
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