[Schurkey]

Originally Posted by Sirrotica

Article about what companies make filters with return lines and why they work, along with part numbers and pictures.

https://esgcapitalinc.com/fuel-filter-with-return-line/

1. Wix and Purolator are both owned by the same parent company--Mann + Hummel. Best guess is that the Wix and Purolator filters are identical...buy whichever is less expensive.

2. MOST GM cars with "vapor return" have the vapor outlet on the engine-driven fuel pump. Connects to the same sort of plumbing as these filters would connect to, only the location is different. Specifically, the filter--placed between pump and carb--would vent vapor AFTER the outlet check valve(s) in the fuel pump, while a vapor-return nipple on the pump vents vapor after the inlet check valve(s) but before the outlet check valve(s). I have no idea how the before/after check valve issue affects operation except that you can expect all fuel between the fuel filter vapor-vent, and the needle/seat area of the carb(s) to vanish down the vapor-return plumbing when the vehicle sits awhile--and it's going to take some cranking to push the fuel back up to fill that plumbing again. OTOH, venting vapor directly from the engine-driven fuel pump will make the pump more efficient.

3. I am VERY hesitant to put HOSE on the pressure side of a fuel pump. Installing these filters between pump and carb means you've got sections of hose on the inlet, and the two outlets of the filter. There are plenty of OEM applications that do this...but you'd better be inspecting that hose on a regular and frequent basis.

[Sirrotica]

The return limes usually have orifices in them to only meter vapor at a high rate, and fluids at a much reduced rate. The return lines usually are plumbed above the siphon point of the carb, and the tank so that they don't empty the lines upon shut down.

The Kawasaki engine on my Ariens mower is plumbed like this and one time it came detached from the clip that held it elevated, the gas flooded the carb until I realized the hose was no longer at a raised position. as soon as I clipped it back the flooding ceased.

I have seen some bypass filters on certain applications that were hard line plumbed between the carb and pump, but that is the exception, most are neoprene hose. To be fair when this type system was implemented in the 60s there was no ethanol added fuels to accelerate the deterioration of gas lines. The gas line material was also of better grade that it is today.

Chrysler was the most outspoken when ethanol blended fuels were mandated in the 70s that the OEM materials they used in manufacture were breaking down prematurely when exposed to the ethanol blended fuels. They argued that they weren't going to warranty the problems associated with ethanol fuel deterioration because their systems were designed for pure gasoline.

[3X24SPD]

Hi Bob, did you ever check the fuel pressure before- and then after you made the swap to the new filter/return?

[zippy]

I went to a Holley Blue pump at my tank many many years ago for this reason. Refills the carb when Key on so there no more 3 min of cranking to get fuel up. LOL
Right now I am also incorporating a Oil Press Sw and a push button. So, havent run her in a few days, I know carb will be empty, I can push the button for 5 sec or so. You can hear the pump note change when bowl is full. Then start as per normal. But if I just came out of a store, Just start her, Fuel pump will automatically start when oil press switch closes. AND, if engine stalls, or an accident, oil press drops, switch opens and fuel pump shuts off for safety.

[Goatracer1]

Sorry never did a before and after comparison.

[3X24SPD]

Fuel pressure is/was clearly the root of the problem.
If you swapped carbs, then whole intakes (to TriPower carbs)- and still had the same exact issue- that's telling you something.
The return you installed is now bleeding off just enough fuel pressure through that orifice to make things happy.
Should have checked the fuel pressure first, before going through all that work you did.
At that point, you might have said "Wow- 9psi- must be time for a new Fuel Pump!".
What is interesting to me though- is that 61-67 Pontiacs actually used that Filter with the return in production.

[Sirrotica]

Something I ran into decades ago when Pontiac was having all the nylon timing gear failures. I had a customer car that a timing gear replaced, someone didn't get the eccentric installed properly making the fuel pump stroke much longer than it would normally be, raising the fuel pressure too high because of the increased stroke.

Replacing the eccentric to it's original position cured the problem, just something I ran into many years ago that can cause too much fuel pressure with a stock style pump. Might be worth checking if your fuel pressure is exceeding the capacity of the needle and seat.