How much horsepower can a mechanical fuel pump handle?

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asked Jul 23, 2023 in Repairs/Maintenance by Ratpleased (2,980 points)
How much horsepower can a mechanical fuel pump handle?

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answered Aug 23, 2023 by Wendell (42,480 points)
A mechanical fuel pump can handle up to 900 HP.

The biggest difference between a mechanical fuel pump and electric fuel pump is the mechanical fuel pump uses the engines crankshaft or camshaft and engine power to operate the fuel pump and an electric fuel pump uses electricity from the battery to operate.

The electric fuel pump has an electric motor for in tank fuel pumps and for inline electric fuel pumps they use magnetic force and work like a solenoid to pump the fuel.

Mechanical fuel pumps require cranking the engine to pump the fuel and electric fuel pumps only require turning the key to get the fuel pumping.

The advantage of an electric fuel pump over a mechanical fuel pump is the electric fuel pump provides instant fuel pressure to the carburetor without needing to crank the engine to provide fuel pressure.

With an electric fuel pump you can more easily prime the carburetor before starting the engine.

The disadvantages of a mechanical fuel pump include the reliance on the engine to to drive the fuel pump, diaphragms failing, no constant fuel pressure, possible leakage of fuel into the engine crankcase caused by a ruptured or leaky diaphragm, vapor lock in the fuel pump, fuel pressure drops and faulty diaphragm spring etc.

An electric fuel pump uses the battery to keep it on and can provide instant fuel pressure and constant fuel pressure.

A mechanical fuel pump cannot and will not pump too much fuel.

The mechanical fuel pump uses the engine to operate the fuel pump and diaphragm in the fuel pump so it won't pump any more fuel than it needs.

Electric fuel pumps though can pump too much fuel and if the mechanical fuel pump is going bad it can pump too little fuel or no fuel at all.

You can replace a mechanical fuel pump with an electric fuel pump as long as you have the correct fuel pressure that is not too high.

If you use an inline electric fuel pump then the fuel pressure should be just fine but if you have an intake electric fuel pump then you will most likely need a fuel pressure regulator to keep the fuel pressure at the proper PSI.

You do need a fuel pressure regulator with an electric fuel pump if the electric fuel pump produces a fuel pressure higher than 7 PSI.

Some fuel pumps such as inline fuel pumps will only put out at most 7 PSI which is okay for a carburetor engine but in tank fuel pumps can put out higher fuel pressure and in that case you would need a fuel pressure regulator with the fuel pump.

The PSI that an electric fuel pump should be for a carburetor is between 5 PSI to 7 PSI.

Carburetors don't require as much fuel pressure as a fuel injected engine as the carburetor just needs enough fuel pressure to fill up the carburetor bowl and then the carburetor sends the fuel into the engine.

You can hook up an electric fuel pump to a carburetor.

Carburetors can use either electric fuel pumps or manual fuel pumps.

An inline electric fuel pump will work just fine for a carburetor on a vehicle, lawnmower etc.

The amount of fuel pressure that is needed for a carburetor is only about 4 PSI and for a fuel injected engine it requires around 60 PSI of fuel pressure to work properly.

If you put an inline fuel filter in backwards the pressure of the fuel system may not be correct and it will not filter correctly.

In some cases an inline fuel filter put on backwards may not cause any issues and in some cases it may restrict flow.

A fuel line can be too big and a fuel line that is too big can take longer to pressurize and could have a drop in fuel pressure as well.

It can take a larger pump to pump the fuel in a larger fuel line.

Fuel lines should be sized correctly to get the correct fuel pressure and prevent fuel leaks as well.

Fuel line length does matter as the longer the fuel line the more pressure it will need to get the fuel to the engine.

However most times there's no worry about the length of fuel line from the fuel pump to the engine as the fuel pump should provide enough pressure to send the fuel to the engine.

You can use rubber hose for fuel return line as long as it's rated for fuel.

It is OK to use rubber fuel lines for fuel as long as the rubber hose is rated for fuel such as gasoline and diesel.

The size that most fuel lines are would be 3/8 inch size.

The most popular fuel line sizes are.

-6AN (=3/8" OD)
-8AN (=1/2" OD)
-10AN (=5/8" OD)
-12AN (=3/4" OD)

You can use braided hose for fuel line as long as it's automotive type braided hose and rated for fuel.

You cannot use braided hose that is rated for water or non fuel as it can degrade and leak.

But use of braided hose such as stainless steel braided automotive fuel line is good and can be used for fuel including gasoline.

Polyurethane tubing can be used as fuel line as polyurethane is resistant to gasoline, diesel and most other fuels and chemicals which make it an ideal tubing type for fuel lines.

Vinyl hose will not work on fuel lines as vinyl cannot withstand the contact with fuel and will degrade and leak.

Also gasoline and other fuel tends to make a clear vinyl hose go hard, and when that happens the pipe may become brittle and the seals at each end may be compromised.

Silicone tubing and hoses are not resistant to gasoline as silicone hoses are porous and not suitable for fuel or oil.

Stainless steel can be used for fuel line as it's resistant to fuel and good for high pressure as well.

The best material for fuel line is braided stainless steel fuel line that has much higher heat resistance and withstands high pressure liquid better than other fuel hose.

Rubber fuel hose is also good for fuel line.

Fuel lines don't usually need Teflon tape if you're using compression fittings.

However some fuel lines may need Teflon tape depending on the type of fuel line connector you're using.

You can Zip tie fuel lines to hang them or to also submerge the fuel hose in gasoline or diesel.

Plastic zip ties are fuel resistant and safe to be submerged in fuel.

Nylon fuel zip ties are also fuel resistant and also resistant to most chemicals.

The hose clamps for fuel line should be tight enough so that it's squeezes the fuel line somewhat and tight enough so the hose cannot be pulled off.

Tighten the hose clamp a little at a time and check the hose.

Just make sure the fuel hose clamp is not tight enough to cut into the hose.

You can use polyurethane tubing as fuel line as it has exceptional resistance to most gasoline, oils, kerosene, and other petroleum-based chemicals, making PU tubing and hose an ideal choice for fuel lines (although additives in today's gasoline and petroleum products warrant field testing).

The kind of hose you can use for fuel line is rubber fuel line hose that is rated for fuel.

SAE 30R7 hoses are designed for fuel.

Rubber hose that is rated for fuel can be used for return fuel line as well as pressure fuel line.

When using rubber hose for fuel line pressure make sure the rubber hose is rated for the fuel under pressure.

However any fuel hose that is rubber will be okay for fuel return line.

However just note that regular non fuel rated rubber vacuum or heater hose should never be used in fuel applications.

The hose will deteriorate from the inside out and can plug fuel filters and carburetors with rubber debris, long before it springs an external leak.

SAE 30R7 hoses are designed for fuel.

These can go under the hood and are typically used for low-pressure applications like carburetors or a fuel return line.

It can also be used for PCV connections and emissions devices.

SAE 30R9 hoses are designed for high-pressure applications like fuel injection systems.

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