74ZZ430

I'm using a 1721 Edelbrock fuel pump which Eledbrock claims puts out a maximum pressure of 6 psi. I am see over 10 1/2 at idle which is causing idle problems. The pressure does drop down to six at full throttle, which means I can't use a regulator beacuse they need a minimum of 4 psi difference in inlet and the regulated pressure and I need to hold at least 5 1/2 for the nitrous system. I talked to edelbrock and they weren't much help. I did install the part # 1797 bottom plate. Any suggestions
Thanks

After Shark

Sounds like a bad fuel pump. I'm guessing this is a mechanical pump. If so they are suppose to be internally regulated. If it doesn't maintain and they are not willing to help, then I would return the pump and get another or another brand to try.

Triple_Wild_Bill

I had a similar problem on a previous car. Too much pressure for The Carbureter Shop's Quadrajet. I solved the problem by adding a Cagle vacuum operated fuel pressure regulator. The Cagle is adjustable. I ran 3 psi at idle. When I'd romp down on it, the pressure would climb back up to 7. Q-Jets are known for not liking much fuel pressure.

cardo0

I don't know what type of carb your using but unless you want to replace that fuel pump with hi press or an electric, you may need to change carb inlet needle & seat and possibly float setting. And for a ZZ430 you can handle a much bigger area inlet valve seat vs stock motor & carb. Probaly something due for a change anyways.
Now I'm right now in process of building new hard line fuel line including a regulator and filter from my new Carter mech pump to carb. It will have a small 1/4" recirc-line from regulator to that vapor return line (along side of 3/8" fuel supply line). Doug Roe's how to book on Q-jets says a recirc will help prevent vapor lock and keep fresh/cooler fuel at carb. He recommends 0.020"-0.060" orific size for a controlled leak. But hey, I've read posts that say using one of those dual outlet Fram fuel filters work just fine and Doug Roe mentions them too. So for a quick test I'd plumb one of those cheapie little Fram dual oulets up with rubber fuel hose and see how that works. I guess I'm trying to say you could just add a small recirc line without regualtor. I'm going with the small orifice and hard line as Doug R. mentions a lot recirc will entran air into fuel in tank and create a lot of fuel vapor in tank .
But if try it post your results for me will ya.
Good luck. cardo0


[Modified by cardo0, 6:29 PM 6/27/2004]

74ZZ430

Thats for the suggestions, I will look into the vaccum operated regulator. I replaced the first 1721 pump with another 1721 and this one runs at about 9 psi. I put a tee in the line and ran that to the 1/4 return line, first with a .045 restrictor which caused to much of a pressure drop at high end with the nitrous on. I purchased a set of nuimber bits that go down to 80 and drilled a .023 hole in a piece of aluminum stock which lowered the pressure to about 8 1/2 psi and at least allows all the pressure to bleed off the carb when the engine is shut off and still maintains about 5 1/2 psi on top end.
I'm using the original q-jet with a .130 inlet.

cardo0

Wow great timing Double Z. I'm getting ready to drill holes for my recirc. Man this forum is great. Check out my post this forum as I just plumbed into the fuel inlet of my Qjet to get my press reading and recirc as close to carb as possible - be carefull here.
Another suggestion for yours would be to add another orifice(s) in series to slow leak/recirc flow (use some space/volume between Os). BTW what type gauge are you using to measure fuel press. Just a heads up those liquid filled gauges are worthless as they can't compensate for heat and will produce bad readings - sometimes peg low (or high, can't remember).
Well sounds like progress and sure beats plumbing and wiring up an electric pump. Please post any improvements. cardo0

74ZZ430

I've tryed two gauges and they read very close. What I think I'm going to do is put a normally open solenoid in the return line, which will allow full return of the fuel , which does drop the pressure by about two pounds and have that wire to my nitrous arming swith which will completely stop the fuel return when I have the nitrous armed.

cardo0

Quote: ...What I think I'm going to do is put a normally open solenoid in the return line, which will allow full return of the fuel , which does drop the pressure by about two pounds and have that wire to my nitrous arming swith which will completely stop the fuel return when I have the nitrous armed.

Nice work and tricky idea. Hope you feel safe with that set-up (I have no experience with NOx).
I kind'a think that your fuel supply line may be a problem here. I didn't like the stock flex hose with tight 180* S-bends from supply line to pump - too much restriction. Realigned my Carter pump inlet & outlet to allow a gradual 180* flex hose over pump to inlet. Also no 90* tubing fittings (brass inverted flare fittings). Straight brass inverted flare fittings only for mine and gradual tubing bends made with a tubing bender. Found 45* fittings at local NAPA but hopefully can do without and use the rounder tubing bends (tubing bender from Harbor Frieght). Doug Roe recommends 1/2 fuel line from tank to pump for hi hp big blocks (which may apply to your motor) - but more work than I'd need for my set-up.
Just a little more unsolisited advice but hope it can help. Lets us know what works and what don't. cardo0