I've been having some problems with my fuel pressure(can't get below 70lbs) and the local speed shop guy says I should be running #10 line to the regulator and #8 for a return. does anybody agree?
I have 06 now and the stock miata return line. The Aeromotive regulator calls for 99% return line for idle.
If you've gone through this drop me a line. He says it will burn up the 255 pump shortly if the lines aren't big enough.

 

I have an AN6 supply and run the stock return with a cheap Ebay regulator. I have adjusted it from 20psi all the way to 80 with a battery charger on, engine off. It now sits rock solid at 40psi.

This is with a Walbro of course.

You need to find a new speed shop. The outlet for the walbro is 3/8's, or AN6

 

I've been Googling all around and can't find anybody that agrees with him. BUT I still can't get my pressure to go down below 65lbs at idle. The tuners says no problem but it still isn't right. I'm going to have to go under the car and pull the return line and see if it is flowing a nice stream back near the tank, and I don't have something obstructing it. Thanks for your imput.

 

bypass the regulator and see what kind of pressure you get. This will tell you if its the return line

 

I use 3/8 or -6 for supply and return on both of my walbro 255 pumps. I use them on a carbed application and use my aeromotive bypass regulator to drop my pressure down to 5.5 psi. I have not had a problem with the pumps yet I have 10k miles on the swap. Is the regulator plumbed correctly? Did it come with two springs? Is there a Boost/Vacuum Reference Port that needs to be plugged? This is the regulator that I am using http://www.summitracing.com/parts/AEI-13301/?rtype=1 . The bottom port is the bypass port and the other four can be used for inlet or outlet.

 

from 3psi to 65psi? That is sick! I assume they have an "EFI" spring and a "carb" spring in the box?

 

Comes with two springs. Very nice regulator. Its worth every penny.

 

I decided I would put the car up on stands and go from front to back with the return line and see if that could be the problem. My connection at the regulator was fine so I went under to where the Miata return line connected up to the stock clip on line to the tank. I put a gas can and hose on the line and turned on the key. It flowed nicely at that point. so I went to the tank and uncovered it and desconnected the other end of the return line and again put a hose line to a gas can and it flowed well. I pulled the top of the tank and removed the guts for inspection on the bench. With air pressure high the air moved through everything well. With it reduced to 40lbs it didn't move so well. HUM! There is a little flow regulator (at least that what I think it is) mounted with two nuts on the tank return line. I pulled it off and used air again on this regulator and it seems to restrict the flow. So I thought I'd experiment and remove it. After putting everything back on, I hit the key again and the pressure had dropped way down at the fuel rails, telling me that it was working now and I was able to adjust it back up to 55lbs. Took the jacks out and after a test drive it was so much better and had that top end speed that had been missing. I have a dyno on Wed and can't wait to see it perform again.
Anybody else experience andything like this?
Steve