Fuel tank return side block-off, for carbed 914s... Options

[DougC]

OK, I replacing a fuel cell with a stock fuel tank on a 914 that's got Webers. The stock tank has 2 ports at the bottom, one for feeding the engine and the other is a return. My understanding is that the return is not necessary for carbed engines..So, my question is how do I seal up this extra port on the bottom of the fuel tank? TIA..

Doug C

[brant]

Doug,

your mostly right.. Its not totally necessary to have a return on a carbed car...
You could just pinch and fold over a stock tank outlet pipe...


but I would recommend that You DO run a return...
You will run cooler fuel if its circulating... more Hp..
better to run a return in my book
brant

[ArtechnikA]

what i did on my car was to attach a 4" (or so...) AN-6 hose with a hose clamp at the tank outlet nipple and a straight AN-6 hose end at the other end. screw in an aluminum AN-6 plug and ta-da, built-in fuel drain. 'course i never needed it after i did that ...

[DougC]

Where does it circulate back FROM, on a carbed car does it return from a fuel pressure regulator or someplace on the webers?

Doug C

[SirAndy]

leave a couple of inches of the rubber hose on the return plastic line, take a 13mm bolt and press it in there, then use a hose-clamp to seal off and tuck it away under the fuel pump.

voila!
(IMG:style_emoticons/default/wink.gif) Andy

[brant]

I wish I was more computer savy.. then I would draw you a diagram... but I'm not so I'll try to 'splain....

from the entrance into the engine bay... you "T" into carb number one... then across the motor and a second "T" into carb number 2....

then into a regulator that will create back pressure for the carbs... (good to mount the regulator not leave it hanging, and also a guage)

finally back down to the firewall and return to tank.

brant

[DougC]

Yeah Brant you really lost me there, I've thought about it over and over and read that explanation several times and can't figure out what you ment, I even tried drawing a picture as I read - no good. Sounds like you'd have the pressure regulator just before the fuel line entered the tunnel to return? This is easier than I'm making it, I'm sure..

Doug C

[brant]

sorry for the confusing explanation...

how do I paintbrush a picture and then post it onto the board?

anyways, the regulator is topside above the engine sheetmetal and in the engine bay, but it is after the carbs and not before....

it then creates back pressure depending upon how open it is adjusted, and thus the fuel guage allows you to read the amount of back pressure......

a "T" in the fuel line for each carb and then the guage and then the regulator and then back below the motor to return through the tunnel....


oh.. I didn't mention this before. I'd recommend a filter before the first carb.

hope this helps.
brant

[datapace]

If you DO want to block it off, check out JWest engineering:
http://www.jwesteng.com/fuel.htm

I ordered two fittings from him a while back, one was for -6AN for supply, the other was just a cap for the return. He will make one if you ask. I didn't like the idea of the hose end with a bolt in it, it seems like a good solution until the hose deteriorates or a clamp loosens.

How's the fuel supposed to stay "cooler"? Before it gets to the engine, what's heating it up? Especially if you have the fuel pump up front under the tank?

-datapace

[Eddie914]

It all depends on what type of fuel pump and pressure regulation system you are using. If you are using a high pressure FI fuel pump with a bypass type fuel pressure regulator, you definitely need the return line.

If you are using a low pressure fuel pump for a carburetted engine, the return line is not not needed unless you are using a bypass type fuel pressure regulator.

[ArtechnikA]

Where does it circulate back FROM, on a carbed car does it return from a fuel pressure regulator or someplace on the webers?

the 914.6 fuel pump, for instance, is a recirculating pump with a built-in regulator; one thing the recirculating feature does is continuously filter the fuel.

in a FI engine, pressuring the fuel heats it a bit, and in some race cars, a small heat exchanger is built into the return loop to reject heat to the airstream. i can't see this being a significant factor in a carbed car, but if you did have a way of making the fuel cool (e.g. cool can...) recirculating the fuel through that would be A Good Thing. last i checked, SCCA permitted a 1-qt cool can in at least some SOLO-II classes (Prepared and above, for sure...).

[brant]

other SCCA classes are cool can friendly too.
I know locally the spec-7 guys can't get through a session without a cool can...

it is a mandatory item locally for lots of track cars (of cours rotarys are pretty hot)

I think the higher altitude reduces the effectiveness of cooling and makes it more of an issue too...

but by having the fuel fully recirculate, it is not sitting in the engine bay backed up behind a fuel regulator and gaining temp....

yes more plumbing
yes not necessary for a street car
but still one of those things that is more good than harm, and could save you from re-plumbing later if you decide to go tracking.....

brant