Having fuel pressure issues - have always had them since my swap.

1992 - was TBI car, now carbed 350, in-tank TBI pump, Mallory 4309 regulator, Edelbrock 1405 carb

I can't (and never have been able to) get my fuel pressure below 6psi. If I back out the adjustment any more on the 4309, it falls out. Had another 4309 laying around, tried it, same result. Also tried another brand new guage, same result. 4309 is within 2ft of carb (as Mallory recomends), and guage is within 6in of carb.

Was looking at the 4309 directions - states that minimum 3/8 return line is required, smaller causes a restriction in returning fuel, thus increasing presure. Then looked at car - return line factory hose connected to metal hardline in engine bay clearly reads "5/16". Also, it's nearly impossible to squeeze this rubber line onto a 3/8 fitting.

Edelbrock carb instructions clearly state at no time should fuel pressure ever be above 6psi - they recommend 5-5.5psi at most.

Having trouble getting a decent tune out of my carb - always have. Idle mixture screw adjustments don't seem to make any difference unless all the way in or all the way out (where at either point car dies of course). Sometimes it'll bog down instead of accellerate when it's warm (210+ temp), sometimes it will die on a fast tight turn (Edelbrock says this is a high fuel pressure issue). Car just seems to run rich no matter what I try.

So ...

1) Am I correct? Is the stock return line 5/16?

2) The feed line is the larger one (3/8) right? (that's what it states in the carb swap article)

3) Why am I the only one having an issue with this?

There's hundreds of members here using the stock TBI pump and 4309 without issue. I've even checked with Barry Grant, Quick Fuel, Aeromotive - they all state that if the return line is smaller than the feed line, there's going to be a fuel pressure increase with their respective return-style regulator products. I haven't read of many folks changing out fuel lines - the few that mention it here are doing it for repair purposes, or to fed a large hp gas sucking HP beast.

Is anyone else running rich or having issues with fuel pressure?

4) Or, is my tuning issue something else?

Any ideas greatly appreciated.

 

I did some testing - if I attach a 3/8 line to the return on the 4309, then I can adjust the 4309 down to almost 0psi - so the 5/16 line is causing the problem.

I played with carb a little more, and reduced some richness out - no more black exhaust marks in driveway from unburnt fuel, but still rich.

So - I assume that most other folks running this setup were running rich as well.

Is my next step a timing change with carb readjustment after?
Or a rod/meter change in the carb?
Or am I going to have to replace the return line (I really don't want to)?
Other options?