1979 gas tank question
 

Hi guys, I am in the middle of swapping a 91 s5 motor in. I have swapped the fc cross memeber and suspension and I am almost ready to try to crank however I have hit a road block.

When running my new fuel lines I attempted to trace them back to the tank and plug them in appropriately however I am not certain that I have done it right.

Is there any way to know or test to ensure that I have the feed and return right.

Right now i have the feed to a 90 degree solid pipe that is farther back and on the right..I have the return on one that is a little closer and runs much more vertical. Also the one that I have run as return seems to be smaller diameter than the one i have run as a feed.

The issue is that now with all of the lines run the feed line is just pumping air....

Thank you for your help!

simple way to find out witch one is return and witch one is main line.
is to cap one and put air pressure in the other and if the presser just excapes and no fuel comes out its the vent. try the other side one should pore out gass.

I just happen to have my tank out of my SA and the lines are still on it labeled.

So with the tank positioned like it was in the car there are 4 hose connections. I'll reference the front most one as number 1 and work my way back.

The first one is the return line and its smaller than the feed.

The second one is the main fuel feed line and its larger and sticks up higher than the first.

The third one is for the cut and check valve and can be capped or connected, your choice.

The rear most one goes to a fitting in a rubber gasket and thats the vent line. If you cap it off get a vented gas cap.

Hope that helps.

This question leads me to believe that you did not pull the sump out of the 79 tank. The tank will need to be converted internally to run FI (if FI is the route you going with the 91 S5 motor).

IS the sump removeable on the SA tanks? For some reason I seem to recall them being welded in place prior to the FBs.

tank is welded and sealed gas pump is inline not in tank.

Perfect! Thank you so much guys, this was exactly the information I needed. I know its an inline fuel pump stock because I pulled it off, it is just really confusing trying to trace the lines back to the tank!

So I think I have had everything hooked up right all along...Hmmm...I wonder why I am not geting fuel...:scratch:

I understood the pump is behind the seat under the car. But I thought that a non-FI tank needed a bigger sump like what is in the GSL-SE tank to work with FI. It also needs a bigger return line.

Yea it was right where You said it was...I have run much bigger feed and return lines but as for the sump I may be confused as to why it needs a bigger sump...i dont think there is any access into the tank so I hope i dont need to weld in another one because I would have to cut a big hole! ahh!

I'm not sure about the 79 tank, but Trochoid on the board does a mod on the first gen 12A tanks where we takes the sender level out of a FI tank and puts it in a non-FI tank. Once the tank is dropped, there are screws on the top to remove the sending unit and sump. The sump is just a bigger area that hold fuel for FI.

Only the S3 tanks have removable fuel supply/return units and only the SE tank has a sump cup. All the earlier tanks have the fuel lines brazed to the tank and no sump. I have pics posted in the archives showing the differences between the carb/FI S3 tanks. Your tank will not look like the S3 tanks. If you can locate an S4 tank and install the cup and fuel supply/return unit along with the intank pump, it makes for a much cleaner upgrade.

https://www.rx7club.com/1st-gen-archive-71/fuel-interchangeability-fuel-tanks-facts-604917/

Imho, the stock carb feed lines are too small for FI. The SE supply return lines are probably larger than needed as all later FI rotaries had slightly smaller lines.

my 1979 rx7 gas tank as 4 hose connections...
The rear most one goes to a fitting in a rubber gasket and thats the vent line. If you cap it off get a vented gas cap.
What can you do if you can not find a vented gas cap, and my vent line connection is broken and no good???
I need help badly!

has* not as