TLDR - can I run inline style with a "t" before the inlet to make my own de-facto bypass style? For the E21, running a Weber 38.
Short story long - Currently have an old Mallory 4309 on it, but it gave up the ghost. That said, only getting 5 or 5.5lbs at the carb, and it runs pretty well.
It seemed to like 3.5lbs best, easier to tune, a little easier to set for good off idle, etc.
Cheap arse bastage that I am, I don't feel like spending $100 + (on the low end!) on a nice adjustable one if I don't have to.
Since an inline one only "sees" the inlet pressure, if the t-off is small enough, think it would work?
Or likely to not be able to do that since it would be too low a system pressure with the T? Fuel line is ~5/16, maybe if the T off is 1/8 (or smallest brass fitting available at Ace)?
I've modified a Holley non-bypass into a bypass type. I think the lower pressure one is the 12-804 and it is only deadhead. Probably a youtube video out there that shows you how.
How did you modify it?
Something akin to my thought above, or is there a provision/space to drill and tap somewhere?
I was going to try to type it out but I would be trying to talk with my hands while doing it,lol.
I found a video for you
I was able to hold low enough pressure to keep an IDA happy on a rotary even while using an EFI fuel pump(I think it was for a Ford truck)
I actually found that very same vid!
I don't have a drill press, nor a place to put even a small set up, so that route is problematic (sigh. I miss my 3 car garage with ample space everywhere...).
Years and years and YEARS back, on the blowthrough carburetor mailing list (it was a long time ago...) people had a way of running the Holley type regulators as a bypass type, as well as converting them to boost reference.
Info is long, long gone, of course. But IIRC it was as simple as running the fuel pump to the "outlet" of the regulator, with the carburetor teed into that line, and the "inlet" becomes the return. I think.
I mean, this was like over 25 years ago, I'm happy that I remember that it's possible at all 
In reply to Pete. (l33t FS) :
I think that would work, but also...
... I picked up a bypass type for relatively cheap on eBay, even though the lowest rated fuel pressure was still to high.
Since the inline and bypass type look like they share the same architecture, my thought was to use the rebuild kit for the inline one and use the lighter psi spring (rebuild kit comes with a diaphragm and "high" and low pressure spring).
Turns out the Holley 12-803BP regulator (I think that's the p/n) doesn't use the spring and diaphragm set up, the diaphragm sits on a spacer.
So, after watching the video above and thinking about what that dude said about spacing for the diaphragm, I took out the non-spring diaphragm and spacer, played around with washers to get a "lower ride height" on the spring diaphragm, and voila, 3.5psi to the Weber.
In case anyone is a CAMF like me and wants to know if they can make it work.
Sure, I could've spent $100-$125 on a decent bypass type and been done in 2 minutes, but, why do that when I can waste an hour or two and be in for half that amount?
Maybe don't answer that question....
Makes perfect sense at my $7.35 hourly rate! I always figure I'm happier in the shop tinkering for no money than working for someone else at $100/hr.
