Return fuel line with carbs?, Anyone running return fuel line with cabs? Options

[rhodyguy]

Get the self regulated carter pump. Keep it simple. Put the return line in the tunnel while you're in there so it's ready if you go back to fi. Cap both ends, the return spigot on the tank and leave it alone. Single supply to a Tee in the engine compartment. One line to each carb. Keep the carb lines off of the engine tin. Stock phenolic spacers under the intakes help with the heat. Some expensive hp pump, a gauge and regulator?

[bbrock]

What's up guys! I just purchased a pair of Dell 40's which I'm currently rebuilding at the moment. I like the idea of running a fuel return for 1.7 as some have discussed but my question has to do with the fuel pump and regulator set up. Can you run a low pressure (rotary style) fuel pump i.e. (CB Performance / Carter) with Option E and delete the regulator from the drawing? Or would I need to keep a high pressure set up with a good aftermarket regulator like Mallory ect. to make up for the amount of flow for the return and not flood the carbs?

It looks to me like E would work with either a high or low pressure pump, but you would need the regulator regardless. Otherwise, you'd just be circulating fuel around with no pressure built up beyond what little the resistance in the return tube would provide. It also seems like a low pressure pump would be better. But I have no actual experience with these, I'm just thinking through the plumbing.

[rgolia]

Not sure I get the return line need/benefit with carbs. I have driven a carbed 914 2.0 for over 70,000 miles with no return line and never had a problem. That includes driving from San Jose CA to New York City during August 1984....and I was in a rush too. Now, the first 70,000 miles I put on my 914 with fuel injection is another story....had a few extended sit and waits on the side of the road back then. (IMG:style_emoticons/default/smile.gif)

[bbrock]

This is just from what I've read on the Internets, and we all know how infallible those Internet experts are.. but there are potentially 3 benefits, none of which would make the car necessarily run better. These are:

1. It keeps cool fuel flowing to the carbs (okay, that might make it run better if vapor locking is an issue).

2. Pump doesn't have to work as hard since excess pressure is bled off in fuel sent back to the tank. Theoretically, the pump might last longer.

3. Return line is there in case you ever go back to FI.

Little things, but fussing over these cars is part of the fun. (IMG:style_emoticons/default/beerchug.gif)

[1adam12]

Thanks
rhodyguy
bbrock
rgolia
For the input. I guess it's another debate regarding cooler fuel temps to run or not run the return line with dual carb set up. Everyone seems to not have a problem with either variation of fuel line set up. I can definitely save some $$ by just getting the rotary fuel pump and just running a simple layout to the dual carbs.

[1adam12]

Get the self regulated carter pump. Keep it simple. Put the return line in the tunnel while you're in there so it's ready if you go back to fi. Cap both ends, the return spigot on the tank and leave it alone. Single supply to a Tee in the engine compartment. One line to each carb. Keep the carb lines off of the engine tin. Stock phenolic spacers under the intakes help with the heat. Some expensive hp pump, a gauge and regulator?

On the dual dells, one carb has a dual union fuel inlet and the other a single. Is the dual union originally for the return or to daisy chain from to the second carb. I know you mentioned about using a "T" on the fuel line to the carbs but just wondering the function of the dual inlet union. **Sorry guys I'm ordering the Dellorto Tech Guide tonight**

[brant]

also...

I've run many a rotary or low pressure pump with return line systems
so no need to buy a special pump


I would add... in theory at least... the cooler fuel promotes more hp
so because my application is a race car, its worth the additional effort. I also use insulated sheeting/wrap on my fuel lines in the engine bay... same idea... cooler fuel.

race cars often run fuel cooling canisters... I know I briefly had a spec R7 and those were considered mandatory for hot rotary engines running at altitude. also note that we have a race in Colorado at Snowmass - aspen... I don't know the altitude... but probably 8000 ft? altitude effects cooling... air mass effects cooling... anything that could prevent a problem is worth considering


not something you may be able to feel
but why did the factory go with a return line on the 914/6 ?
all cars made in the last 30 years use return lines

I can not tell any difference with or without the return on my fuel line when judged by seat of the pants.... however any and everything that could be better is worth considering.