hooking up electric fuel pump

[jaegzie]

I have an electric fuel pump 2-3psi. When i hooked up the fuel pump the car seems to flood itself out then i shut the fuel pump off and the car runs great for a shile then shuts off when it runs out of gas. Is this a carb issue or is there something special i need to do besides running the wires direct to the battery and ground. The gas is being pumped from a gas can right now.

TIA

 

[Trevor Jessie]

Carb issue. Does gas pump out of the carb float bowls if you leave the pump running?

 

[jaegzie]

When I first hooked them up I didnt have one of the return lines on real well and it shot gas out, i havent checked recently though. I will take a look tonight and get a better description of what is going on.

 

[Trevor Jessie]

Those aren't return lines. They are for vapor collection. The floats in the carbs should lift and shut off the valves. So either your floats are not floating or you have crude keeping the valves from fully shutting off.

 

[jaegzie]

intersting, Ill have to look at the setup better, That could be causing the problem right there I imagine. I will pull up one of the 69s and make sure everything is the same. Thanks again.

The other question I had was... Will the eletric fuel pump still kick off when the floats fill up? or how does the electric pump know when the carbs are full? This is one thing I am clueless on :blush: so be gentle when making fun of me on this one!!

 

[Trevor Jessie]

Some pumps turn off when they reach a certain pressure. Others continue to run, but can not move fluid once a certain pressure is reached. So, the float/valves are designed to hold back about 3 psi. If your pump puts out more than this, then the carb bowls will overflow.

 

[Sarastro]

Check the fuel pump output pressure to be sure it's not too high. If you are indeed getting 2-3 psi when it's flow is completely stopped, that should be OK. Much more and it can force fuel past the needle valves in some cases.

I can tell you how a mechanical pump works, so it doesn't pump when the flow is stopped, but with electrics it probably depends on the type of pump. In any case, it's not terribly important; all you need to know is that the pump's output pressure builds up to some maximum and that's it. Just need to be sure that maximum isn't too high.

 

[Bayless]

If it's a SU pump then it is just an electromagnet, a spring, a couple of one-way valves and a diaphram. Some other pumps work this way too. The magnet pulls the diaphram which pulls fuel from the tank through one valve. At the end of its stroke, a set of contacts open to release the magnet. The spring then pushes the diaphram back which pushes the fuel through the other valve on to the carbs. At the end of its stroke, the contacts again close to energize the electromagnet, starting the process all over again. When the backpressure from the carb needles closing exceeds the spring tension, the spring can't push any more fuel out. So, it keeps pressure on the output line until some fuel is used from the carbs, letting the float drop and opening the needle.