Fuel system design help

[Matt Harwood]

Hey guys,

I've decided to get the original vacuum tank on the '29 Cadillac working properly. Right now it runs on an electric pump and a regulator, but 1) it's noisy, 2) it takes valuable electricity to run that would be better used to power the headlights, and 3) even regulated down to 2 PSI or so, it's still too much pressure and the carb loads up at idle. I figure those are all good reasons to get the vacuum tank operational.

My plan is to run two separate fuel systems and keep the electric pump as back-up. I'm going to fit a T to the gas tank outlet, run two separate lines forward, one to the vacuum tank and one to the electric pump. I'll install another T before the carburetor and join them there. That way I can run it on either system depending on conditions. I'm also trying to locate check valves that will work under 1 PSI so that the pump doesn't fill and overflow the vacuum tank when it's running. I feel that this is a safer and more permanent solution than a momentary switch and using the fuel pump to simply fill the vacuum tank. I don't want to be on a tour and have to hit a button every few seconds to keep the vacuum tank full--I forget that kind of thing.

Anyway, what size tubing should I be using and what material? I'm leaning towards stainless since it'll last forever, but would copper be more correct for 1929? What about metal fatigue with the copper? What size, 1/4", 5/16" or 3/8"? I'm going to use hard tubing as much as possible to avoid rubber hoses and clamps, as well as ferrule-style fittings which should be more than adequate for this low-pressure system.

Does anyone have any other advice on this? I'd sure appreciate some guidance before I start buying parts and materials.

Thanks!

[rons49]

Matt, I think I would go with the 5/16. Many cars of that vintage used 1/4, but I believe you will get more volume with lower pressure. McMaster - Carr sells the check valve you want. Steel line should do fine. Would not waste money on stainless, if you can find it. Bending is difficult. Copper is easy to bend can stress crack faster then steel, but is an absolute no-no for brakes(hydraulic). Should be OK for low pressure fuel. What was original? Regarding the regulator... What type are you using. Check out Summit Racing they sell a regulator that will adjust down to 1-4 Psi using an hex key . The dial in type are not accurate, and are noted for leaking in short time.

[HarryLime]

You said you "Decided to get the original vacuum tank Working properly". Why do you need another fuel system as well ? So many cars used vacuum tanks for so many years ,Yet with todays technology we need redundant system ? That's too nice a car to mess with an electric pump. It just needs nothing more. As for tubing, what was there ? Steel will out live us both, copper too if you want the easiest and quickest way. Great auto, I saw it at Stan Hywet.

[rons49]

I argee with that, mostly. Try the original system with the rebuilt vac tank. But, out here in AZ many guys' cars still fuel starve do to the lack of pressure on the volitility of the fuels that have today. If that is your case, place a solenoid type pump back by the tank out of sight with a true 1 psi regulator closer to the V tank out of sight as well. At the very least, After the car has sat for a while, the electric pump will get the fuel system primed up quickly.

[TexRiv_63]

Matt, I recommend using Cunifer tubing in 5/16" size. Cunifer is a copper/nickle alloy that bends and flares as easily as copper but eliminates the work hardening danger. It also polishes to look just like nickle plating. I did all the lines on my 32 with this material, it made the jobe very easy and it looked great.

[Restorer32]

Yep, we use the Cunifer, available from McMsaster-carr.

[rons49]

Cunifer tubing?? Is that the tubing that Oreillys sells instead of steel( brake line)? Last year I went to purchase 5/16 tubing to change a portion of my fuel line on my Hudson. The counter guy gave me some greenish coated tubing, which I bought but used some where else, because the color did not match the bright steel line already on the car. At a later date, I tried the greenish line on another car, and was impressed how easily it bent and flared. Is that what cunifer tubing is? Ron

[Matt Harwood]

Thanks for all the suggestions, guys. I've pulled the vacuum tank and will be sending it out to be rebuilt. I'll look into the cunifer tubing, sounds like exactly what I need. I'm still going to integrate the electric pump into the plumbing, just because it's there and I like the peace of mind it offers. I'm noting that 5/16" flange nuts are none too easy to find, however. I'll keep looking. I've also found some check valves that operate with as little as .3 PSI, which should be just fine for protecting the vacuum tank from the pressure of the electric pump, while still opening and flowing with just gravity feed.

Thanks for all the suggestions! I'll keep you updated on my progress.

[DavidMc]

I would be very interested to know the source of those low pressure check valves.

I have my vacuum tank set up with a bypass electric fuel pump exactly as you propose for use when the car vapor locks. The check valves are spring loaded and I have reduced the spring tension but I am not confident that they will allow flow from the vacuum tank under gravity and prevent reverse flow when the pump is operating.