Setup:
Carbed 350. Bypass Holley 12-842. In tank, stock TBI fuel pump. See picture below for fuel flow direction at FPR. Barbed adaptor at steel line and standard fuel hose from the return line and feed line into the FPR. The Charcoal canister steel line is cut and crimped closed near the front of the car. No charcoal canister. Aftermarket 2 way vent is installed.

What happened:
First startup try, hit the switch and fuel pump turned on and sent 12psi straight to the carb. Gas went everyone.
What is weird is I pulled the hose off of the steel return line and a heavy continuous flow of gas came shooting out of the steel return line. Also, I took the gas cap off, and heard pressure release.
The pressure I heard releasing when I took the gas cap off is concerning too, but not sure why that is present when I have the vent installed.

My thoughts:
Gas shouldn't be coming from the return line out toward the front of the car unless it's stopped up somewhere in that line, right? BUT before I reinstalled the steel lines, I blew them out real good and they flowed freely. I'm starting to wonder if i've got something crossed somewhere at the tank. But it still doesn't make sense if it's crossed it still wouldn't come shooting out the return?
Ya'll got any bright ideas or theories of maybe what I should be looking for or what i can try?

 

The return line sits at the bottom of the gas tank along side of the fuel pump strainer...I just put a Aeromotive bypass regulator for fuel injection to carb on my 383...also installed a new Aeromotive low pressure guage 0 -15 psi and a high pressure guage 0-100 psi...gas came out of the return line like you are speaking of...I disconnected the pump wiring and ran the carb dry...and opened the gas cap...

 

Try more like...."Higher than ~7 PSI".

Which it is, if it's "Spewing out of the carb". I went through this TWO SUMMERS AGO. Only need a couple PSI to have plenty of fuel for the carb.

 

that is true have mine set at 6 1/2 with a AED 750 double pump with mechanical secondaries...

 

UPDATE: still stuck.
Tried a holley 12-887 this time.
Stuck a bolt in the carb line to simulate the bowls being full.
1) With the return hose feeing into a gas jug - psi was around 3 psi.
2) With the return line connected to the cars return line, it was still 12 psi.

Our theory: The return line on the sending unit was low in the tank and with the gas level high enough to cover that line it wouldn't allow fuel to freely flow back into the tank.

What I did:
Blew air through the return line at the front of car and the line is indeed freely flowing air and not stopped up.
So, I cut the return line high on the sending unit. About 3 inches below the top of the tank with only about 2 gallons left inside the tank....STILL 12 freaking PSI.
I'm at a loss.
After cutting the return hard-line inside tank short: I put a PSI gauge at the end of the hose (carb end) instead of a bolt so that I'd have a reading at the FPR and the end of the line...both still 12 PSI.

 

Just read another thread on here of a guy who said he used this fuel pump in the tank. May be what I have to do idk.

Carb is only a 600cfm. 5psi is plenty ..12 PSI will make it ****.

I've took all the plugs out and drianed the oil. Gonna turn it over a few revolutions before putting the plugs back in and throw some fresh oil in it before cranking it....AFTER I get this gas situation under control, that is.

 

IDK why you cut the return line in the tank, but I'd be scrutinizing the hell out of the FPR (and the plumbing thereof), if I were you.

 

Thanks for the input but 2 different brand new out the box Holley carb rated FPR just happen to both not be working? I find it hard to believe.

 

I don't find it that hard to believe...but note that I also said this:

The regulator is the device that is responsible for....regulating....the fuel pressure. You've confirmed clear fuel lines. You've cut the return...for reasons unknown to me. If you can't adjust the fuel pressure down below 12 pounds with the adjustment on the regulator, I'm sorry bub, but the regulator ain't workin'! Either it's junk, or it's plumbed incorrectly. You should probably vent your gas tank too, since you eliminated your EVAP system.

 

This is a page from the GM 345 HP ZZ3 350 H.O. Camaro engine conversion kit installation manual. This engine conversion kit was meant to be used on 1982 to 1987 carbureted Camaros with the L69 5.0L H.O engine or the LG4 5.0L V8 engine.

This kit came with an in tank 3.5 PSI draw thru helper electric fuel pump as used on some year L69 Camaros and all 1987 LG4 Camaros. This same kit was dealer installed on earlier year L69 & LG4 cars that didn't come factory with it on customer cars with complaints of fuel boiling and vapor lock. Sometimes also installed with a ducted blower fan to blow air over the Q-jet carb to keep it cool.

With this kit installed you modified the fuel pump hanger/sender assembly and replaced the 3.5 PSI draw thru helper fuel pump with the 14 PSI high volume fuel pump (TBI fuel pump on steroids). You removed the engine mounted mechanical fuel pump and replaced it with a Holley adjustable fuel pressure regulator and special mounting bracket that blocks off the fuel pump opening on the block. You reused the metal hardline from the fuel pump to Q-jet and used the 3/8 NPT to 3/8 barbed fitting for the supply line and a special 3/8 NPT to 1/4 barbed fitting with 0.042 inch restriction for the return line.

NOTE: Use only the 3/8 NPT x 1/4 fitting supplied. It has a .042" restriction which is critical to the proper operation of the fuel system.

Why? I don't know. But GM's Chevrolet Race Shop said so. Maybe it's only true with this model of Holley fuel pressure regulator used with this engine conversion kit.

Rant On

This is how the fuel system should be setup with all carbureted 3rd gen these days on cars that do something beside sit in the garage and get looked at. They also should have a heatshield between the intake manifold and carburetor baseplate.

Cars with a Q-jet have it worse because of their small volume, centrally located fuel bowl. It gets heat soaked and stays that way longer and with the small volume of fuel it holds it evaporates quicker.

Put gasoline under pressure and you raise its boiling point. Put gasoline under a vacuum and you lower its boiling point. An in tank electric fuel pump puts the gasoline under 14 PSI of pressure until it hits the fuel pressure regulator then 6 PSI until it hits the carb. A mechanical fuel pump pulls a vacuum on the gasoline all the way to the pump. They also get hot AF mounted to the block. You could say the same about having the regulator mounted on the block like with this engine conversion kit but you could always mount it to the car and run a rubber fuel hose instead.

Gas today is not the same as gas of decades long past. All cars for decades now are fuel injected with in tank high pressure fuel pumps. Gas today doesn't have the anti-varnish, anti-boil, anti-evaporation stuff that carburetors needed decades ago.

 

NOTE: P/N 12-842 is a bypass regulator with idle bleed jets intended for use with drive belt or high pressure alcohol fuel pumps. This regulator comes from the factory with a .040” idle bleed jet. This will give a good starting point for your idle pressure. Each engine and pump combination will be different and will require tuning of the jet to obtain the desired idle pressure. To raise idle pressure, lower the jet size. To lower idle pressure, increase the jet size.

NOTE: Alcohol engines require 3-5 psi at idle and 9-11 at WOT.

I'm guessing that is why the 12-842 regulator has the idle bypass jet.

NOTE: These fuel pressure regulators are marked “in” and “out”. However, due to the design, the regulators can be plumbed either way. For example, you can use the inlet as the outlet and the outlet as the inlet with no negative effects on the fuel pressure regulator operation.

PDF | HOLLEY BILLET FUEL PRESSURE REGULATORS P/N 12-841, 12-842, 12-845, 12-846, 12-847, 12-848, 12-879, & 12-880 Installation Instructions.

 

Airwolfe this is fantastic info. There MUST be something to that restrictor fitting. I think I'll try that today.
Along with checking for a second time that the lines are hooked up correctly.
I wonder, with the charcoal canister hard-line Ive cut and crimped closed....I still have the rubber line hooked to it. Maybe that's doing something. I'm going to unhook that rubber hose from that line and see what happens.

To your point of the Holley being for a belt system. That's why I bought the second one intended for just car. Application old school stuff ..with the same result.

 

A restrictor in the return is only going to increase the pressure to the carb for any given regulator setting...the amount that it will do that will depend on the volume pumped by the fuel pump.

 

Tom the note in that manual shows the restrictor is in the outlet not the return. Yes a restriction in the return would seem to raise pressure BUT the restriction being in the outlet just might be the solution.

 

Way I read it is 3/8" NPT x 3/8" barbed fitting for the tank supply to regulator inlet, 3/8" NPT x 3/8" inverted flare to carburetor fuel supply hardline, and 3/8" NPT x1/4" barbed fitting with .042" restriction outlet for fuel return back to the fuel tank.

I don't know that this restrictor has anything to do with your problem or not. It might just be a Red Herring leading you off on a tangent.

I don't know what car you are starting from or what engine and fuel system it had to begin with. I seem to remember 4 lines. Fuel supply, fuel return, EVAP, and tank vent. I remember 3 sizes. 3/8", 5/16", and 1/4". I remember two of the lines being the same size. Make sure you have everything going to the right lines and don't have EVAP, vent, or return mixed up.

You have an aftermarket vent valve. Maybe back the fuel cap off so loose it's about to fall off and doesn't seal as a test.

It is possible you have two defective regulators. Remember everything is Made in China junk these days. Everything Made in the USA these days is junk too because Americans have been beat to death in life and just don't give AF anymore.

Companies don't have QC anymore. You the customer are the QC inspector.

 

Cool story. Way back in the day when me and my friends were teenagers one of the friends had a rich Daddy. He bought 5 mini crotch rocket motorcycles for him and his friends to ride around on and have fun. He said he bought them and we all had to take care of them. We had a blast. They were full blown mini super bikes in looks but really just hopped up mopeds that could be rode without a motorcycle license. They were fast for what they were.

We did all the upkeep and maintenance on them. Then one year we get them out and they all ran just fine but one. It would start and run OK then just keel over dead. We fooled with it until it was beyond us. Took to the dealer where bought and they worked on it and still the same, took to a ATV dealer had them look at it and work on it and same thing, took to a buddy that raced motocross and worked on his stuff and other people's stuff and he couldn't find the problem either.

Defeated we bought everything at the dealer to rebuild the fuel system. Still would start and run fine then keel over dead.

One of us said "You reckon that rubber hose on the bike that goes to the carb vent is clogged?" I blew though it and sure enough clogged up solid. Took it off the bike and poked a coat hanger into it from both ends and squeezed it were I felt the clog and broke it up. Then blew it out.

It was a clump of dead ants. I guessed climbed up the vent tube going after the sweet smell of old varnished gasoline and got overcome by the fumes and died in there.

Bike ran like a champ after cleaning out the blocked vent hose.

Sometimes chasing down these problems runs you nuts.

 

Lol great story. Sometimes it's the simple things. I think I'll start at square one, making sure these lines arent crossed up somehow. Then work my way forward.
FYI it's an 88 camaro that was an original TBI car. New thank, new sending unit etc.

Thanks to all of you for your input on this. For the fun of it I'll post an update once I get this squared away.

 

My bad...I misunderstood "outlet" as meaning the return/outlet back to tank.

But, I don't agree about the restrictor. Especially at idle where fuel consumption is low (fuel velocity through the restrictor is extremely low, thus the restrictor is not a restriction). If the restrictor is "lowering the pressure"...then you really don't even need an FPR, do you?

The FPR should be able to drive the fuel pressure all the way down to 0 PSI
*If it's working
*if it's plumbed correctly.

 

That's a gooder.

I got two sort of like that one...We had a snow cat at work, that developed a problem where the engine would randomly die. It could go two minutes and die, or it could run for two weeks without any problem. Obviously, when it was running fine, it was hard to diagnose a problem that didn’t exist. After trying a number of things, we had an idea and pulled the sending unit from the fuel tank, looked inside—and there was a latex glove in fuel tank! It would randomly get sucked into the fuel pick up, then when the cat would die, it would float away.

How did a latex glove get into the fuel tank? The operator lost a fuel cap, then thought a mechanic’s latex glove would work. As the fuel was consumed, the glove was sucked into the tank and the troubles started.

The other similar one was similar to ^that^, but we got a little sidetracked looking for the problem. The operator was convinced that it was a drive system/calibration issue. I tried calibrating the drive a couple times and kept getting the same complaint—that the cat had no power. Finally, in a conversation with the operator he said, “...right before the cat dies, it”—“Whoa, hold on a minute,” I said to the guy, “It DIES!? That’s not a drive system problem, that’s a fuel problem!”

After that I started going through and checking the fuel system. There are red, plastic caps the vendors install at the factory in all the ports and fittings of the fuel tank. Someone must have just pushed them into the fuel tank during assembly rather than pulling them out. One of those plastic plugs was getting sucked up into the pick up tube. It had a tiny hole in it that would allow just enough fuel to run the engine most of the time, but not enough flow for the engine to create real power.

...and that last one is what a "restrictor in the outlet line" can/will do. Limit top end power, and/or make it starve under heavy demand.

 

Question....
If you have a carb that ran great until you accidentally push 15psi through a carb and it floods
THEN fix everything to only flow 3-5 psi and it continues to flood THEN you adjust float level and still floods.
It's dribbling out both venturis no matter what I've done.
What should I be looking for?
blown power valve maye?
Anything else you can think of that may have been damaged from running 15 psi through it?

 

Needle and seat assembly maybe?

What did you do to finally get the pressure down?

 

That and CONFIRM that you really have 3-5 PSI at the carb.



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