For reasons unknown, I swapped out the fuel injection system for a carb. The FI pump delivers about 10 psi and the two barrel carb requires 5-7. Is there a restrictor I can put in-line? Do I need the fuel return line back into the tank?
Any other tips?
Thanx, Dan
what you need is a fuel pressure regulator, not a plain restrictor. if you used an oriface type restictor it would still overpressurize when demand from the carbs was low, and probably not have enough flow to the carbs at max demand. I think that you can get adustable low pressure regulators from places like summit and gegs. ggod luck.
,NO , you can put a "T" in the line and run the fuel you dont need back to the tank. they do make a regulator that you can install. its ?? $130. the T is $0.130.
return style regulator - send the extra fuel back to the tank so you dont overheat the pump
A "T" won't regulated the fuel pressure and quite possibly your pressure will dip below what you need, a return regulator is what you need, Holley units aren't expensive and they are reliable.
For what you are doing Dan, a return style regulator is perfect.
Fuel flow should go:
Pump - Carb - Regulator - Return line
IIRC there are cheap ebay carb regulators patterned after the Holley unit in the $25.00 range shipped, just make sure you are getting a low pressure return style regulator.
GVX19 wrote: ,NO , you can put a "T" in the line and run the fuel you dont need back to the tank. they do make a regulator that you can install. its ?? $130. the T is $0.130.
So you just put a T in the line between the pump and the carb and run one back to the tank? Is that gravity-dependent or something?
I've always wondered about running electric fuel pumps in carbed cars, I've seen a few cars that do it but I haven't had a really good look at how they're set up. Both my cars have mechanical pumps and they're not going to last forever, and I probably won't be able to replace them (although that might not be the best solution anyways)...I've been thinking of running redundant fuel pumps in my sammy for reliability.
1st Gen Rx-7's have 4Bbl Nikki carburetors and have electric fuel pumps. The pumps are already designed for carb applications though.
If you're using a high-pressure fuel injection pump then you need a low pressure carburetor friendly return-style regulator. As others have said the Holly is a good unit. You want the regulator before the carb though, it won't do much good after it as the high pressure will destroy the carb.
An FI pump that delivers 10 PSI? Wowsers, that's low. Most of them will hit the 45-60 PSI range and the regulator will drop it to around 36-38.
You should be able to use a Holley return style regulator to get the pressure where you need it , though. You'll need some way to keep the return line pressurized slightly. The aforementioned RX7 Nikki carbs had a return line check valve which kept residual pressure in the return line so the carb won't starve on hard acceleration.
GM throttle bodies work at low psi 9.5psi - 14.5psi with a 10psi standardoperating pressure.
TBI injection pumps use low pressure, but still need the return line and need the pressure to be up there to prevent run out.
On a previous car I used the stock pressure regulator from the car set up to conect the fuel supply and return lines. (Stock fuel pressure regulators are really just relief valves that relieve excess fuel back to the tank if it comes in at a higher than desired set-point.) This kept the fuel pump and lines and everything happy and gave me a pressurized source of fuel at the front of the car at too high a pressure for the carb. Then I connected one of the cheapo pressure reducing regulators from the supply line to the carb.
Sure it's two regulators, but the non-return carb regulator was so cheap it still saved me $, and this way I didn't have to worry about the pump either.
Jensenman, I was guessing at the psi, whatever it puts out is too much for a carb.
FWIW, this is a Geo Metro fuel pump and a Motorcraft 2100 2bbl carb.
Dan
Hmm. Wasn't aware the TBI's used pressure that low. Good to know. BTW, we ditched the TBI fuel injection in favor of a carb on our LeMons car, we are running a Holley 'red' pump with an adjustable regulator, both of which came off of my freebie J-H. We are even running points, that way we can fix anything on that POS with a hammer. 
A restrictor would reduce the flow but not the pressure. A simple pressure regulator is all that is needed. Run the least amount of pressure that will still supply the carbs requirement.
This setup was a Holley 650 double pumper with the stock Mazda fuel injection pump. In order to bring it down to the correct pressure, I ran a T in line before the carb, with a regular adjustible carb pressure regulator between the T and the carb, and a return line off the other side of the T. Never had a problem with the carb in 5 years of street and autocross use.
In reply to iceracer:
This thread from 2009...brought back by a canoe.
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