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Garden Tractors Discussion Forum

Fuel pump

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Rusty wheel

11-21-2023 09:07:21

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Wondering how these little fuel pumps work. What makes them pump fuel? I put a new Brigs engine in a JD 111 but it didn't come with a fuel pump. So I installed an electrical pump from NAPA. I put a flow control valve ahead of the carb but It either gets too much fuel or not enough fuel. Thinking of installing a fuel pump from a 176. Just wondering how they work and if it will solve my problem. Thank you much.

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11-22-2023 06:00:47

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 Re: Fuel pump in reply to Rusty wheel, 11-21-2023 09:07:21  
You never followed up, what was the solution to your 325 starting problem?

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Rusty wheel

11-24-2023 09:58:13

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 Re: Fuel pump in reply to Blackhole49, 11-22-2023 06:00:47  
I haven't worked on it anymore. The starting relay is $77 from JD. Gonna try the wiring suggestion I got in the replys. Thank you very much for your inquiry>

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11-21-2023 17:37:35

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 Re: Fuel pump in reply to Rusty wheel, 11-21-2023 09:07:21  
I am thinking you are asking about the pulse type fuel pumps that are commonly used on small engines. They are a small diaphragm pump.

The principle they work on is that as the piston goes up and down in the cylinder there is a corresponding fall and rise in the crankcase pressure. (Actually the manufacturers try to create a small vacuum at all times to keep the engine from blowing oil out the seals, but still there is a rise and fall in the pressure, even though it is less than atmospheric pressure all the time.)

They use the changes in pressure in the crankcase to operate that small diaphragm pump. It has check valves (usually rubber flaps) that allow the pump to force a tiny bit of fuel toward the carburetor every time the pressure goes up in the crankcase.

I have put a pressure gauge on them before, I have never seen one develop more than two psi, even with the carburetor line completely pinched off.

You can install one of these pumps on an engine that did not originally have a pump. If the engine is apart, just drill and tap for a 1/4 nipple in the crankcase well above the oil level. You want your hose to the pump to not have any dips in it because if it fills with oil the oil will dampen the pulses and the pump will quit working. It is best if the pump is mounted high and the pulse hose runs up to it.
Briggs and Stratton connects their single cylinder fuel pumps to the dipstick tube. It has the nipple for the pulse line molded into it. This might be an option for your replacement engine, those dipstick tubes shouldn't be very expensive.

The other thing that sometimes happens is that even at 2 psi, sometimes the pump can blow fuel past the needle valve and cause the carburetor to flood. Single cylinder Briggs and Stratton engines with carburetors set up for a fuel pump usually use an inlet needle seat with a noticeably smaller inlet hole for the needle to seat against when compared to a similar carburetor intended only for gravity feed fuel delivery. Because the needle seat hole is smaller the inlet needle can hold back the flow of fuel and also, because it has a small pressure, there is still enough fuel available to operate the engine under all loads.

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Rusty wheel

11-24-2023 10:06:58

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 Re: Fuel pump in reply to T.R.K., 11-21-2023 17:37:35  
Many thanks for your reply. You told me just what I wanted to know. I think I'll try a lower pressure pump.

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wore out

11-21-2023 11:07:46

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 Re: Fuel pump in reply to Rusty wheel, 11-21-2023 09:07:21  
I recently installed a Facet electronic fuel pump from NAPA on a John Deere garden tractor and it's working fine, 1 - 4 psi rating, IIRC.

What's the pressure rating of the one you installed?

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11-21-2023 09:33:45

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 Re: Fuel pump in reply to Rusty wheel, 11-21-2023 09:07:21  
I believe the karting guys use pumps that rely on engine vacuum. There's probably a forum or two that discuss all things karting.

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