The restriction is not in the line from FPR to below the engine. That pipe is fine. It's in the next section that runs over to the passenger side then along the frame, back to the rear axle. My guess is that the restriction is the end of that pipe where it was crimped to make the saginaw fitting. As I said before, the i.d. of that end of the pipe is much smaller than the pipe end that goes into the bottom of the FPR, yet both are 1/4" pipes with crimped saginaw ends. And they are both original from the factory. My theory is all the original return pipes (except at the FPR) were crimped down too much, which wasn't a problem with the original low pressure fuel pump and FPR. But when you replace them with a higher volume pump (like Walbro 340) and adjustable FPR, now the BLMs drop way down because the fuel pressure is too high with vac line on.
In order to prove my theory, I'd have to cut off the end, then connect it to a new braided line going up to the FPR. I haven't decided yet if I want to do this, replace the entire line that runs along the frame, or replace both lines (from FPR to rear axle). The first option is certainly less expensive.
Oh, what I did for a temporary fix was make changes to the chip so less fuel is supplied at idle and while driving. (I make my own chips.) The BLMs are back to 128 +/- 4 but I'm still going to replace the "restriction" with braided hose, probably 6 AN. A 4 AN will probably work fine for my street driver but I believe the correct adapters are only available in 6 AN.
