leeperryracing

I recently added a carter inline electric pump to help out the mechanical but with the added volume, the stock 5/16" return line has become a big bottle neck by backing up pressure in the regulator and flooding out the carb because it can't return the fuel "efficiently" to the tank. I though it was a bad regulator so i called aeromotive to get some quick tips....the first things i was asked was what pump/pumps are used and the return line size....I told the guy it was the stock 5/16 return line, he almost crapped himself! said i was lucky the diaphram in the regulator is intact. I did some tests he recommended and with a 3/8 return line, everything was working very good but he suggested a 1/2" return line for my power levels. So, will some 1/2" braided line be "easy" enough to route from the reguator all the way back to the tank?(eliminating the 5/16 completely). What y'all think? any road blocks I might run into?

Lo-tec

If you make the feed and return lines the same size there will be no backup in pressure.

Apeiron

Which Carter electric pump did you use?

leeperryracing

that makes sense but the 1/2" line won't hurt right?
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the part# is P4070: 4-6psi, 72gph....using an edelbrock victor mech. pump with it.

Apeiron

I have a hard time believing that pump is outflowing a 5/16" line.

five7kid

Do you have an output pressure gage on this? Is it going above 6 psi? If it isn't, the return line isn't to blame for your carb flooding.

jstoltz

If you end up changing the line I would go with SS hard line under the car and just use the braided in the engine compartment. It isn't hard to bend line. just take the old line out and use it for a template and make sure you are using a 37 degree flare for the AN fitting on the end going to the braided line. also adding a sump kit helps. This is how I plan on running mine.

leeperryracing

there is also the edelbrock victor mech. pump on the block too in conjunction with the electric one.....a 5/16" line is not by any means "big".

leeperryracing

five7, i have a 2 5/8" autometer guage mounted in the hood cowl area(non-liquid filled) and its bouncing all over the place....6psi @ idle, 7.5-8psi part throttle and 8-8.5 WOT if i can get that far without it flooding out and falling flat. I tried 2 other autometer guages i borrowed from buddies and also an el cheapo tiny summit brand one and they all behaved the same way. With the help of an aeromotive tech, we figured out its the small size return line causing the backup in pressure in the regulator which is why the guage is reading so erratic. I took a piece of 3/8 rubber hose from the return port of the regulator and stuck it in a gas jug, then run the engine for a little to prove our theory and guess what! fuel pressure was rock solid, the guage was now registering even minor pressure adjustments and it will stay wherever I set it now without bouncing all over the place and the regulator doesn't tick so hard like a bad exhaust leak anymore, its almost dead silent now...that poor regulator was constipated by that 5/16 return line. With that figured out, back to the original question.

five7kid

I'd suspect a restriction such as a kink or smashed spot on the return line, rather than the size of the line itself.

leeperryracing

nope, no kinks or restrictions in return line.....I had the car on a lift and traced the line all the way back as far as I could still see it and smooth bends all the way! its just that them two pumps together move good volume and the fuel needs to return "efficiently" so the regulator can do its job properly. I have a "stealth" aluminum tank built by rick's hot rod shop which is internally sumped with the A1000 pump, filters, lines etc. inside....i'm just tempted to tear down all the stock sh*t and put that one in and all i'll need is two lines, -10 feed and -8 return, nice and clean...the tank has a little vent tube welded on the top already so don't have to worry about a third line. I wanted to save that tank for my twin-turbo project that will sit in my other '86 Z28 though. By the way we were all rooting for you at PINKS!!! I didn't even qualify because of that PITA fuel press/delivery problem.

five7kid

Two pumps? What two pumps?

leeperryracing

a carter inline electric prt#P4070 and an edelbrock victor mech. on the block

Apeiron

The Carter P4070 has an internal bypass regulator set at 6 PSI. It's not enough pressure to overcome the internal bypass regulator of the mechanical pump at 10 PSI. The P4070 also only free-flows a measly stock-ish 72 GPH, which is well within the flow capacity of a 5/16" line.

What regulator are you using after the mechanical pump?

leeperryracing

the regulator is an aeromotive prt# 13301, those two pumps will flow more than enough volume and pressure to run both the motor and the 125 N20 hit....just need to get that return line ran so the system can do what its supposed to. Do you have any ideas as far as "hooking" a -6/-8 return line to the tank WITHOUT dropping it?

jstoltz

You should drop it. If you are rerunning the line You will HAVE to drop it. If you are doing that though invest in a sump kit and just do it right. It will cost around another $125 but that is for a sealer kit and sump kit and paying to have it welded. If you know what you are doing well it will save you around $35. This way you won't have to worry about it ever again. Or try to save on it now and then find out you will have to do it later, your choice.

leeperryracing

I was fearing that i'll have to do that...i'm not too big on the "cut a hole" idea in the rear hump area. Looking at the comp. engineering kit with the 1/2" npt in/out or would the 3/8" one be plenty?

89RsPower!

This may be a stupid question, but why do you need two pump anyway?

five7kid

Which spring are you using in it?

jstoltz

why do you want to cut a hole in the rear hump? a sump kit installs on the bottom of the tank. there have been some on here that have added an access door to th etank and sending unit by cutting a hole but I haven't seen any that looked all that great. I guess it could be a feasable idea if it was done correctly (including framing it and sealing )but that wasn't at all what I was referring to. That would be OK for a street or cruise car but if you are planning on putting down some strip times get rid of as much weight as you can without sacrificing structural integrity.

leeperryracing

because either one by itself won't be enough for the motor and nitrous....i've seen a few motors go under because people put all the eggs in one "weak" basket.
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I was talking about just doing the return line only, not the sump and so that was a way to do it without dropping the tank....but gonna go ahead and do the sump so no need to cut any holes in the rear hump area to get to the tank door.
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i'm using the low pressure spring....0-15psi

jstoltz

doing the sump now will save you some headaches later on anyway. Modify the sending unit to accept an -AN line for the return so it will still come out on top and then use an NPT to AN fitting on the sump for the feed line. and weld up the line that use to be for the evap cannister unless you are still using it and do the vent however you want.

leeperryracing

between the full length of feed from the sump to the regulator and from the return port to the top of the tank, I ordered 40ft of -8 braided hose(better to have too much than too little), AN hose ends, NPT to AN fittings and the comp. engineering sump kit. For the venting of the tank, i might just do away with the evap canister completely....don't think its doing a good job of venting anyways. Theres a piece of rubber hose(stock) that goes to a little breather/vent thing right above the axle....that sucker is CLOGGED! i bet both that and the piece of rubber is been on the car since it left the factory('86) so replacing those and "making" my gas cap into a REAL vented piece, there should be no problems with horrid pressure build up in the tank....now on to the fun part which is dropping that damn tank

jstoltz

stant makes a vented cap for our cars

Apeiron

The volume of the two pumps in series isn't additive though.

89RsPower!

yeah I've never heard of doing it that way.. I have a seperate line and pump for my 200 shot..

leeperryracing