BrokeLoser

I’m converting from manual fuel pump and manual choke on a Weber carb to electric Carter fuel pump and Edelbrock carb with electric choke. Counter guy at the parts store is claiming that since I’m going with an electric fuel pump I won’t need to wire the choke up.
Why would he say that?

duke460

An election tric fuel pump turns on with the key. If you wait a few seconds it will pressurize the fuel bowl to 2-3 psi. When starting the vehicle fuel will flow almost immediately. On an manual pump the bowl will lose pressure after it sits. Should still pressurize in a 10-15 seconds of cranking I still keep my chokes when I convert to electric pumps. Feel you still need it.

keith ohanesian

smccormick

Two entirely different functions. Cold engine needs a rich mixture to start unless you are always starting in fairly warm condition. Electric pump delivers the fuel to the bowl, choke fattens up the mixture to aid cold start.

BrokeLoser

Right...my thoughts as well...so even though the float bowl pressurizes almost immediately with an elec fuel pump we still need a proper air/fuel mixture for different conditions. That’s why it didn’t make sense when the parts store guy said it.

tunnles

When starting first time for the day the choke just needs a quick flick to get the initial rich mix into the manifold and to the pistons and should start instantly !!
The choke will not have to be used at all for the rest of the day !!

My VEE 4 2 STROKE outboard even after sitting for 11 months i just pumped the bulb up hard and a quick flick of the choke and instant start ! never had to be touched the choke again till the next morning ! summer, winter hot or cold was always the same thing every time !

GaryDoug

He is wrong, probably thinking of fuel injection.

prowlersfish

That's why he is a parts guy and not a tech . Did he tell you how to wire the pump so its off when there is no oil pressure ?( needs to be done) , and its a spark protected marine pump right ?

BrokeLoser

He didn’t...but I am aware of the required low oil pressure switch...I am wiring one inline.
I don’t think I’ll go as far as to wire in a relay with it to help reduce cranking time....Your thoughts on that?
I usually stay with the idea that fewer connections on a saltwater boat is always better.haha

billinstuart

Wrong.

1) A fuel bowl on a carb is not pressurized
2) Fuel does not "flow" from a carburetor
3) The float bowl is full all the time, even when sitting.
4) A carburetor float bowl is like a toilet tank.
5) A choke is a mechanical device intended to enable the engine to pull MORE fuel for a short period when the engine is cold.

bladenbullet

only in a part store....

bills description is probably the best abridged version ive ever seen...

when an engine starts cold a rich mixture is required due to fuel resisting vaporizing, pooling in the intake and just plain not getting to the combustion chamber....its a very short duration event just to get the engine started....the choke plate on a carburetor reduces the amount of air entering the engine and allows a very rich fuel air mixture....as soon as the engine starts, a vacuum break partially opens the choke plate to allow normal but continued rich operation as the engine warms up....then a thermostatic spring or heater element opens the choke plate completely to allow the mixture to return to normal....

a fuel bowl is never pressurized and always holds fuel regardless of what kind of pump is used to deliver fuel to it...a needle shuts off the flow of fuel to the bowl when it is full...the "pump" required to start an engine shoots a squirt of fuel into the manifold for that rich start up mixture...that function is accommodated by the accelerator pump on an automotive style carburetor....

the only thing an electric fuel pump in the line would eliminate is the necessity to pump the primer bulb...as the pump could draw fuel up and push fuel to the carbs without assistance...although your application sounds like an inboard mounted engine....

some engines have an electronic enrichener that adds fuel when the ignition key is depressed to assist with cold starts...this is how many outboards overcome the lean cold start and run situation....

it gets a lot deeper than that when we involve the actual physics but thats it in a nutshell in laymans terms....

mitchell master

Why convert to an electric pump ?

billinstuart

Now there's a GOOD question.

LouC

What you need to know:
The Edelbrock carb uses an electric choke heater. The choke closes from spring pressure but the electric heater in the choke housing is what OPENS the choke! So if you don't hook it up it will never open and you will be running on an excessively rich fuel mixture all the time. So follow Edelbrock's instructions and hook up the electric (OPENING) choke....Holleys are the same way......

alloyboy

If fuel does not flow from a carburetor then how does the fuel get into the intake manifold?

Dacman

This is what I was thinking. The electric choke thermostatic element either gets heated by a low voltage resisted current from the distributor or engine heat, it should open up after the engine heats up but will be very slow to do so without the electrical connection.

seahorse

don't listen to parts people. Most of the time they get the information confused or completely inaccurate. Unless they show you something in factory service literature, it is best to talk to a technician.

There are plenty of parts personnel who know their stuff and may even be mechanics previously, but how do you know for sure, unless you know their background and reputation.

If you develop a good relationship with your dealer, you come to know the employees and what their strong and weak points are.

mitchell master

controlled leak.

LouC

google "Bernoulli's Law" and the venturi effect

The area under the venturi in a carb is in a low pressure area. IE, the air pressure drops there because the air flow must accelerate as it passes through the narrowed area under venturi above the throttle plate. The fuel in the bowl is at atmospheric pressure, approx. 14.8 psi. So the atmospheric pressure in the bowl, actually pushes the fuel into the lower pressure area under the venturi. When the choke is closed, it further lowers the air pressure there and causes more fuel to be pushed out of the bowl into the venturi, via the idle jets and emulsion tubes. The emulsion tubes add air to the fuel flow to atomize it and make it easier to burn.

This is also how an airplane wing flies. The top of the wing is curved (in cross section) the bottom is flat. When the air flows over the top of the wing, it speeds up and the air pressure on the top of the wing is lower than that underneath it. Therefore the wing produces lift. Now if the pilot pulls the nose of the plane up too high it disrupts the flow on top of the wing and the plane can stall. Bernoulli's Law. I learned this back in the late 70s when I bought a book on carbs to learn how to rebuild the Autolite 2100 2bbl on my 1970 Ford Torino 302.

alloyboy

If I have a leak in a can such that the stuff is coming out is it flowing out?