Fuel regulation questions

Xavier · #1 (**permalink**) 12-04-2006, 12:54 PM

I have a 140GPH electric fuel pump with a regulator mounted before the carburetor, I have a gauge mounted on the fuel line going to the Edlebrock carb. I have the fuel pump running off of a manual switch, which I do not know if it is a good or not good idea. When I have the fuel pump on, and the engine was not being turned over, it was at a too high 12psi. When the engine's ignition start running to be turned on the fuel drops to what I need it to 4 to 5.5psi. THis makes sense to me, because I understand that the fule line is building up with pressure, until the carb needs it and it is higher because there is no place for it to go, but I am afraid that once the carb goes to except the fuel as that there suddenly becomes too much to gulp down at a surge of 12psi. Make sense? Mine seems to be plumbed like everyone else's I see. I just want to make certain this is right. Not that familiar with carburetors and it does not seem right.

RobbMc · #2 (**permalink**) 12-05-2006, 10:49 PM

Dead-head (non-return) regulators only work correctly when the engine is running because there has to be at least a little flow for them to regulate. Return (bypass) style regulators will work even if the engine is not running.

vettestr · #3 (**permalink**) 12-06-2006, 07:43 AM

Xavier,
I did see the Gage is reading after the regulator and before the carb so properly plumbed. If you have 12 PSI before starting engine the reg is not working right. I hear what Rob suggested and respectfully disagree. A regulator should not vary output pressure some 200+ percent between flow and no flow.
With a non bypass type regulator the flow is dead headed every time the float in the carb is at the top adjustment and flows again when needle and seat open again or a constant on and off cycle. Most stock needle and seats will be overcome by 12PSI and Edelbrocks web site mentioned 6PSI is what their street pumps flow. Regardless pressure should remain at set point on output at flow or no flow within a small % of change if working right.
A bypass type regulator flows regulated fuel at pressure to the carb and all additional flow is sent out the return port of the reg.
As a footnote to your wiring of the electric pump you mentioned it was through a toggle switch for on/off. As safety concern you should have a impact or G-force sensor in the line before the pump (available aftermarket or salvage on all newer injected cars). These often have a rollover function built in as additional CYA. If using a key to start engine I would also wire so key is in the ON position to enable the pump.

Xavier · #4 (**permalink**) 12-06-2006, 07:24 PM

Thanks for your reply. Its confirmed, the fuel regulator is bad. Another brand new part failed...

Any idea where I can get one of those impact or G-force sensors (new). I can not seem to find them any where...

Thanks.

vettestr · #5 (**permalink**) 12-06-2006, 08:35 PM

Well they are expensive from a dealer and in most cases have only been used 1 time in their history if you get it from a wrecking yard. Try any late model wrecking yard. Mustangs to Jeep, about any late model injected car or truck.
PS>>>> All cars consumed.... for donor parts have one or had one