Return line, can it be smaller than the feed line?

-
Cope

Cope

Fusing with fire
Joined
Oct 20, 2009
Messages
6,737
Reaction score
10,191
Location
San Jose, Ca.
I'm about to start on the back half of my car and will be running 1/2" line and -8 fittings.
Do I want the same for my return set up or can it be -6?

Thanks.
 
Nope, low pressure. HIGH VOLUME...

Turn it up to eleven, kinda volume....
:)
 
Our dirt cars on alky run a -10 supply -8 return out of the regulator.
 
I would say it depends on your setup and fuel requirements...motor size, Compression ratio, blower, dual carbs...all factors to be considered when factoring line size and return!
 
Can go one single large carb or two 650s (twin carbs more for looks than HP tho..)

Currently running a single 950DP.
but that may change.

May switch to one 1050 or the twin 650s

Just want to build the fuel system once and have it good for what ever changes may come down the road.
 
Should be good to go with the lines you suggested...but if you twin carbs, you may need two FP’s...the Holley Black only goes up to 14 psi output!!
 
Cope said:
Can go one single large carb or two 650s (twin carbs more for looks than HP tho..)

Currently running a single 950DP.
but that may change.

May switch to one 1050 or the twin 650s

Just want to build the fuel system once and have it good for what ever changes may come down the road.
Click to expand...
Hey brother I didn't even read this thread but I just wanted to call you and put this stuff down your PMI me about in pictures. I'll probably point out a few things that was pointing my fingers at a couple things.
IMG_20180719_192518.jpg
IMG_20180719_192546.jpg
IMG_20180719_192603.jpg
IMG_20180719_192616.jpg
 
Okay now that I've done that and got those pictures out I'm going to start with the last picture first and work my way forward. The last picture is a nice little feet of mine that 45-degree bent piece of stainless steel bracket that I built in the parking lot of the apartments I used to live in years ago using extension cord and crude grinding tools. When I had more tools and a garage and made a bracket underneath it that stabilized it from the lower part of the back left drivers corner of the dual-quad plenum. I actually ground a special wrench just to get the nut on behind that bracket. You'll like that too. Anyways I'll take a picture of my cable but it's pretty short going to that bracket and I'm pointing out to the back of the (second from last picture) first hammer on the first carburetor where I attach the cable itself. Attach the back carburetor to the sliding lever at its highest and farthest point from the fulcrum. And the rear carburetor is the one I use for the main carburetor. I even have the electric choke connected to it. It's that real lightly it goes off quickly. But works perfectly. (Side note the carburetor the Chevy guy gave me for free cuz he couldn't get the choke to work! LOL a whole 12 volts will work a miracle!)
On the second picture I'm pointing out to where I have it connected on the front carburetor at a lower or closer to the fulcrum point location. Pretty much the location where I grabbed the rear carburetor with the cable. Anyways that's the one I use when I use it progressively the first carburetor slides through until it hits that stop which is all set up at Full Throttle so both will be at Full Throttle at the same time at the end. Or that piece that's just slid in the middle of the rod and just hanging there for no reason is actually there when I want to run the carburetors one to one and I just put that in that big hole at the top of the front carburetor. I just kind of use it then as a pivot point and I lock it in.
With a real aggressive cam and my 4 Speed it's nice to have it setup progressively as it actually like a wimpy car with the little 600 CFM carburetor and then at about 1/3 of a throttle it feels like all hell breaks loose LOL or you have the same option as one-to-one and just slamming it to the floor and having it all there at once. It's kind of fun to just hot riding around just hitting close to that tightness in the spring when it grabs that second spring and second carburetor. The tends to get a little stiffer as you get into the second carburetor obviously.
 
Even with those pics I still have no idea how your linkage is working....

I'm gonna start a thread and see what folks have done.

Thanks again bud!
 
It CAN but it doesn't have to be. The size of the return line really has no effect on operation, because it's the return orifice that matters. This is why when I plump a fuel system with a return, I use a return style regulator and put it in the return line so it acts as the orifice. That way, you can use whatever size you want, including the same as the supply line and it does not matter.
 
RustyRatRod said:
It CAN but it doesn't have to be. The size of the return line really has no effect on operation, because it's the return orifice that matters. This is why when I plump a fuel system with a return, I use a return style regulator and put it in the return line so it acts as the orifice. That way, you can use whatever size you want, including the same as the supply line and it does not matter.
Click to expand...


There was actually a Barry Grant pump and regulator with a return line and that system used the return line as the restriction. I forget the part numbers of the stuff but I ran into several of them and had to change the return line to make them work.
 
yellow rose said:
There was actually a Barry Grant pump and regulator with a return line and that system used the return line as the restriction. I forget the part numbers of the stuff but I ran into several of them and had to change the return line to make them work.
Click to expand...

You can certainly do it that way. I think using the regulator for the restriction is easier. One less part.
 
yellow rose said:
I agree. Most of the BG stuff I ran into was a PITA. If you did it his way it worked.
Click to expand...

I still remember all the stuff I saw online about metal shaving in carburetors and all. No wonder Holley ended up buying him out.
 
I ran my return line the way RRR stated above. I used a Holley return style regulator 12-803BP. I used the same size line 3/8".
 
The return line can be smaller because it drops the pressure in the main line and it does so very easily. Guys that run a restricted orifice certainly don't have a 3/8 or a 5/16 restrictor. I use a hilborn jet can with no jet. Just the poppet and spring with shims to set the opening pressure. I use that at the back of the car so I wouldn't stall the pump and to knock the pressure down too. Up front I have a standard regulator. Didn't really see the need to have a second line with gas running the length of the car. Or having the main line charged with way more pressure than I needed.
 
J par staged his linkage. Same way Mopar staged the linkage on the street hemis.
 
I just figured his out. Its just pulling in a line. For some reason I thought it was trying to pivot in an arc. I guess it is a arc but the arc radius is very large making the straight pull doable?
 
Looks like jpar is using the rear carb as sort of a primary carb and the front carb as a secondary carb. That front carb has to have the throttle pulled far enough to engage the U shaped bracket the adjustable stop.

Picture one is showing the adjustable stop. The further you move that stop away from the U bracket, the later it pulls the front carbs throttle.

Picture two he is pointing at the U bracket on the front carb.

Picture three looks like he is giving all of us the finger, or he is pointing out the rear carb hiem joint and how he spaced it out so the linkage is in line.

Picture four is showing his throttle cable mount.

So he is using progressive linkage. I never have used it because I always just let both sets of primaries open together and then the secondaries on both carbs open together.

With Holley carbs I pull all 8 barrels together.
 
Cope said:
I'm about to start on the back half of my car and will be running 1/2" line and -8 fittings.
Do I want the same for my return set up or can it be -6?

Thanks.
Click to expand...
fast says so.
 
yellow rose said:
Looks like jpar is using the rear carb as sort of a primary carb and the front carb as a secondary carb. That front carb has to have the throttle pulled far enough to engage the U shaped bracket the adjustable stop.

Picture one is showing the adjustable stop. The further you move that stop away from the U bracket, the later it pulls the front carbs throttle.

Picture two he is pointing at the U bracket on the front carb.

Picture three looks like he is giving all of us the finger, or he is pointing out the rear carb hiem joint and how he spaced it out so the linkage is in line.

Picture four is showing his throttle cable mount.

So he is using progressive linkage. I never have used it because I always just let both sets of primaries open together and then the secondaries on both carbs open together.

With Holley carbs I pull all 8 barrels together.
Click to expand...
You pretty much got it there except for that front adjustment. I tried to allude to the fact that all has to be adjusted at wide open throttle so everything ends up at wide open throttle. You adjust that stopped at wide open throttle and then you get what you get as far as how much of the first carburetor you get before the second one kicks in. Now to adjust that, that would be the distance again from the fulcrum point. And for those who don't know what the fulcrum point is that's the point at from which it pivots. So the closer to the fulcrum point the more the rear carburetor will work without the front carburetor and the closer to 1 to 1 the same distance from the fulcrum point will be one to one. So it was literally determined how far down I drilled that whole as to how much play the first carburetor will have before it grabs the second one.
 
You must log in or register to reply here.
-

Back
Top