The SU pump delivers fuel at 3-4 psi. The carburettor float valve can
shut off and turn on the fuel arriving at that pressure so that it
maintains the level in the carburettor's float chamber (bowl). If the
pressure is much greater, the float valve assembly cannot shut off the
incoming fuel, and the level being too high will cause "flooding"
Since the carb mixes fuel and air, and there is a fairly narrow range
of burnable mixtures, the carb needs to have as many things constant as
possible. Atmospheric pressure is one, and the fuel level is another.
Essentially, if there is too much fuel in the bowl, then you are going to
get too much fuel into the air/fuel mix and the engine won't run right.
It's "flooded" with gasoline, or at least running "rich".
You did not mention in this posting what fuel pump you are using. If
it's an SU, it is probably doing the job OK and the problem is elsewhere.
If it's another pump, you may find, as your friend did, that the pressure
is too great and that a regulator will solve the problem. Or, you could
use a 4 psi pump. There was some correspondence about other low-pressure
pumps a couple of months ago. If you can't find it, let me know and I
will go archive digging for these.
Forget about using the switch to regulate things. That's going to get
you rear-ended when you forget the thing and the engine dies as you leave
a stoplight. Use the switch to keep someone from stealing your car.
On Sun, 05 Apr 1998 00:31:32 -0800 danny <Ldanny@concentric.net> writes:
>I posted awhile ago about my 74 midget not starting, got a lot of good
>advice and are just waiting on another part (new points and condensor
>already bought)- the breaker plate in the distributor (yes, I switched
>the wires and fried one.. DOH! I'm doing all the stupid things ;) ).
>Okay.. here's my question...
>On my vehicle, you have to flip a switch to start the fuel pump. It's
>a little switch under the dash. I flip the switch, hear clicking, and
>then start the car. When it did start it did 2 things. If I left it
>on it died; presumably flooding the engine (what does that technically
>do?). If I started it, shut it off, it would die; presumably not
>getting enough fuel. So I was talking with my Friend Larry, and he
>said if I was going to drive it with this I could do two things.
>Either get a regulator to lessen the flow with the switch on and just
>leave it on, or drive turning it off and on... not exactly feasible.
>So I was just wondering what you knowledgable ppl suggest. I doubt it
>originally came with this annoying switch, so I'm really leaning
>towards purchasing a new one that goes with the car w/o a switch, or
>getting the regulator so I won't have to turn it off and on. I think
>that's all the information...
>I live near San Diego, CA by the way, if anyone wants to cruise by and
>help out a desparate 17 year old wanting to drive his cool covertable
>on these gorgeous spring days! =D