Hello,

I have a carburated 73' 914 with fuel pressure issues. I have tried about (5) different fuel pumps from a Faucet with and without a regulator closed circuit to Holly with a regulator open circuit; and have tried 2 different regulators. My current set up for the fuel pump is in the picture. I have an aftermarket return line on the regulator that feeds back into the top of the fuel tank.

The issue that I am having is that my fuel pressure will not remain constant at the small window of 2.5-3.0 required by Raby ACT for his engine I bought. I have found that the performance is degraded when operating outside of this window.

One major issue I found while trouble shooting was that the tiny breather located near the fuel cap was pinched closed; it is now open. Other than that, I cannot find any other issues for why my pressure fluctuates from 2.0 to sometimes 5.0 after setting the pressure to 2.7 then driving for a while and/or when I start it up the next day, after resetting to 2.7, it will be higher or lower. I just about have to adjust it every time I get in the car and in the middle of a drive. Is there a solution for this? java script:emoticon(':confused:',%20'smid_24')

I will post a picture of the engine compartment and return line tomorrow morning during the day light to give a visual of my set up.

Thanks,
-Reese

Have you tried a bypass regulator and return line? What brand regulator are you using? You get what you pay for with regulators...

Here is a pic of my current set up, it is a $178.00 Aeromotive #13202 A2000 Carbureted Bypass Fuel Pressure Regulator. Part number A27-13202; says it can be set between 2 and 20 PSI.Click to view attachment Click to view attachment

Single steel braided return line from regulator to fuel tank.Click to view attachment

Fuel injection is pressure sensitive, carbs are volume sensitive. I haven’t encountered a return with carbs before, which doesn’t mean it’s wrong but I’d suspect that the fuel bowls may not be staying full fuel because too much gas is being diverted.

possible fuel flow restriction prior to the pump. ever cleaned the the strainer located on the tank outlet? imho all the fancy regulators and pumps are overkill, not to mention the high end braided lines and fittings. in my experience a relatively inexpensive internally self regulated rotary fp is all you need. maybe a quality inline gauge to confirm the self reg pump output.

reese, i'm trying to figure out where the pump is installed. is that the rear trunk or front?

k

I was experiencing the same exact issue. Replaced a bunch of parts. Finally replaced the gauge and the problem that never existed was cured. The gauge I ended up getting was from Pierce Manifold. www.piercemanifold.com .

Good luck

Listen to Kevin on this one. Ask me how I know

What's the setup under the tank up front? My issue was a kinking hose just of the tank out let.

Rhodyguy,

The pump is located in the front trunk. I figured all the fancy stuff was overkill, however I got it to try to fix the consistent fluctuation. I had simple lines, filters and pump originally and I had the problem then too, so I figured all the old stuff was the issue. I got rid of it all and went for new stuff that looked hoping that the issue would be resolved and it would look nice too.
I bought a new strainer but never installed it. I saw the old one and it looked like someone sprayed gray primer on it so i'll pull the tank and install that.
In the next day or so, I will hook up my faucet where I have the holly, and put a gauge right behind it and I will let you know my results. Thanks for your help!

I have a steel braided line with enough slack to lift the tank out so about 1 foot; the other nipple for the return line is sealed shut.

Joe,

I will look into this site to pick out a new gauge. I am very inexperienced in this area... please forgive my, what may seem like obvious answer, questions. Do you think the one I have is faulty? What did a gauge from PM site do to solve your issue? Thanks

Current set up
Click to view attachment Click to view attachment

I understand that ultimately the fuel bowls not staying full will make the engine run rough, but my issue is happening before the carbs I think. The fuel pressure goes up some times and down others even though I set my regulator so that the gauge reads 2.7 and it never stays there. The pic of my current set up in the post labeled "current set up" will give you some eyes on my engine compartment to show what I might be doing wrong.

Could also be the pump speeding up/down either due to current flow or heat problems.

I had a fuel pump in the front that came with 2 hole straps. If the straps were in the right place and the pump warmed up, it expanded the pump just enough to bind on the strap. My pump would just stop working for 5 minutes, but you could still have drag.

If is is a current flow or wiring problem, most likely is a bad ground or grounding point. The 914 electrical system does seem to spike quite a bit. This is evident to the guys that have a volt gauge and turn on the blinkers. larger size wire may also help. If you have a high performance pump on the stock wiring, this may also be a bottle neck for current flow.

You could try to connect the vacuum line on the regulator. At idle (max vacuum) it will reduce pressure. At WOT (least vacuum) the pressure will return to static spring pressure.

So you could use the vacuum to set the minimum pressure and at higher rpm, the pressure would increase. This only works if the diaphragm is still good, it should be if there are no leaks.

You could also try to seal the vac port and see if temp inside the chamber is an issue.

What he says makes sense. I took the tank out to clean it before installing my Raby 2270cc daily driver and saw the strainer looked like someone sprayed gray primer on it. problem was, I took it out away from my home and had to put the tank back in to get back. I ordered the part, its here. So I will get on that asap. So I should install a internal pump too? I feel obligated to ask; so how do you know? lol

The positive wire I have is pretty thin, and it runs from the pump in the front of the car through the car to one of the fuses that gets power when the key is turned one click so I can prime the carbs by tapping the gas. I forger which one it is connected to, but i will use a thicker gauge.

I never thought of using the vacuum line. I called the shop where I bought the regulator from and they said the port that sticks out is for a turbo connection; the regulator is less that 9 months old. Is this port the same as the vac port? If so, how do I proceed? I'm not sure what to connect it to.

i think you will find that all of those breather tubes are pinched - and that you will also find that they actually allow breathing in that status - it's there for vapor capture on emission controlled cars - should be totally irrelevant to carbs

i have found that it only breaths when the fuel tank is pressurized enuf to overcome the diaphragm in the fuel cap

but it will allow fuel vapor smells into your trunk & thereby in your cockpit if it is not vented overboard somehow - especially if it is full open and or you have defeated the oem sealed gascap

The vac port is for a pressurized system but you will see a slight pressure change with it connected. In a boot condition (turbo) it pressurizes the chamber and increases fuel pressure.

In your condition, the vacuum will reduce pressure at idle slightly. Less than 1 psi or so.

Ha, so thats why the inside of my car smells like a gas station! I will route it out of the car. thanks!

Oh ok, but; so should I leave it as it, or plug the removable port? It currently is not connected to anything.

while you cleaned your tank but didn't install the mesh strainer, the first line of defense for the fuel filter is missing. have you tried a new filter? if it's a stocker, they're cheap...toss and replace.

if you soak an old mesh strainer in lemon juice and rinse, more than likely it will have a somewhat brass finish.

read up on that holly pump. jeez...what a monster

and, as said above by several guys - no carb car needs a return fuel line

but carbs do require a open vented tank since the basic physics of "air-pressure pushes fuel into the pump" applies here - pumps don't "suck"

- that is a problem if we are using any oem FI setup 914 & converting it without attending to differences such as the emissions sealed gascap & vapor return system

carb fuel pumps have in internal bypass that obviates the possibility of over pressurizing the lines and a simple inline psi control handles the low 3 psi necessary for webers, etc since a "std" pump is designed to produce about 6 psi min before it "relieves" internally

p.s. - I got one of those Holley pump & psi valve setups on a car I bought running a weber DCOE - "WAY TOO MUCH PSI" - replaced it with a facet and all was well

just to be complete
a carb system will run without a return line

but a return line on a carb system is superior in many ways
more power, cooler fuel. Many fuel systems (including the 914 original system) included a return line in part for this reason

did the factory add a return line to the 914/6 which was carb'd?

so it may not be needed
it is definitely a good thing though

I do not believe all carb pumps have an internal bi-pass
I do not believe rotary pumps have a bi-pass
I do not believe the holley pumps have a bi-pass



to the original poster
this is not likely your problem
but I use those holly pumps also
they have an internal gross filter screen built in
again probably not your problem, but take the bottom apart and check the screen as well as blade/rotor condition

yes, the 914-6 oem pump is a rotary with 3 pipes - has a return, but no psi regulator is used between it and the carbs, so the bypass valve is in the pump head

I have a new one on the shelf

theoretically - - one could simply "tee" the return outlet to the inlet pipe - so no return line is needed

but even the factory recognized the benefits of having a return line and thought it was worth building it that way...

a lot of pumps are build/designed for a specific output and don't need a regulator if that out put is what you want


the holley is designed for around 6.5psi output.... its just not the same output a webber wants.

but that desined output is a different thing than having an internal regulator.

The original gauge I had was an expensive oil filled gauge. It would show pressure sometime, then other times it showed fluctuation from no pressure to extremes regardless of how I adjusted the regulator. I was buying some jets and stuff from PM and decided to buy the gauge they recommended. It has a small spread on the pressure (0 to 15). I installed it and found my pressure was sitting solid at 3 lbs. The needle throbs a bit moving between 3 lbs and 2 3/4 lbs depending on engine RPMs. I think what I'm seeing is the result of the float opening and closing. So, for me it turned out to be a bad gauge. However I'm not running a return line so your issue may be different. If I had it to do over I think I would have spec'd everything for the fuel system from Pierce.

I figured since Pierce Manifold is in the weber business the fuel components they recommend should work, and so far it would seem my assumption was correct.

Hope this helps.
Joe

I have looked up the specs on your regulator and it appears you may not have the right one for your application. I copied this from the instructions pdf on the Aeromotive site.

"The enclosed Aeromotive regulator is designed to be used with high flow (300 gph minimum), low pressure fuel pumps similar to Aeromotive P/N 11202. Performance may be degraded if a similar pump is not used."

http://aeromotiveinc.com/wp-content/upload...09/12/13202.pdf

Your holley pump flows 71 gph at 4 lbs.

That whole set-up seems way too complicated. I use a CB Performance rotary pump 3.5 psi, mounted in the engine compartment, lower than the bottom of the tank, NO regulator, NO return line. I have the screen strainer at the bottom of the fuel tank and a filter after the pump going to Weber 44idf carbs. All the an hardware and steel braided lines look cool but not really necessary.
Cheers, Elliot

well put elliot. another instance where less (fuel delivery system) is more. did you leave the metal canister, a filter, that comes attached to the pump in place?

iirc the instructions that came with the CB unit state that you not mount the pump in an inclosed area, trunks, and to place the pump as low as possible.

k

Pics of the fuel system for my Weber carbed six.

Holley Blue high volume pump
Cartridge fuel filter with shut off valve for easy filter element change
7-15 lb adjustable bypass regulator near pump
1-4 lb adjustable regulator on firewall near carbs with pressure gauge
Bypass line to fuel cell

I ran for years without a bypass line but warming the engine for 10 minutes idling, and sitting in pre-grid waiting to go on track resulted in lengthy idling periods which heated up the fuel pump because it was not moving much fuel at idle. The pump got too hot for my comfort and the fuel also heated up so I changed to a bypass setup. Fuel stays cooler, pump stays cooler and fuel pressure seems to be better regulated.

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Interesting! I guess I will switch out pumps for sure. Thanks!!!