Re: New fuel pump= flooding and gas every whare.
 

Thanks for the suggestion. The good thing about NAPA is they actually have values for pressure and flowrate. Seems like Autozone and oreillys don’t think that’s important.

I don’t want to replace the pump with another one that may have still have excess pressure and get no further forward. I can see how a lot of folks just put on something and let the separate regulator compensate for not having the appropriate pump.

The return line on the installed pump is just capped off, for good or bad. That’s another argument for changing the pump to a 2 line with the lower psi output. Seems like the lower psi (lower flowrate) pumps have 5/16 inverted flare connection, complicating getting to the (probably original) 3/8 inverted flare at the carb.

Re: New fuel pump= flooding and gas every whare.
 

OK, I guess I missed the part about the return line. That pump is made to have the recirculation line free to pump fuel back to the tank. That is probably the issue. Having it deadhead against a plug isn't good for it, and evidently not for the carburetor, either.

Re: New fuel pump= flooding and gas every whare.
 

I have a '71 Jimmy with a 350. [Crate motor now.] The system had the fuel pump with 3 connections input/output to carb/ return line. I put '69 vintage 2 connection fuel pump on it, and delete the return line usage. Works OK.
I had a Delphi [Korean] fuel pump fail on me, right after it's 1 year warranty was up. The pump I replaced it with has been OK since July 2019. So far so good.
I bought an NIB Carter SBC fuel pump from a Craigslist ad, last year. A retired lady sold it for $15. It had been the spare part for the 350 in their Camper. They sold the camper, so she was selling off the spares. After the transaction, I told her how much of a pain it was getting to be to find reliable vintage American-made parts, and how the imports went bust after short intervals. She asked for more money then, but I said ''a deal's a deal.''

Re: New fuel pump= flooding and gas every whare.
 

My local NAPA [Marana, AZ] doesn't carry mechanical fuel pumps for SBCs.
But do you have a part number?

Instead of capping off the return line, buy an earlier iteration [MY '69] mech fuel pump without a return.
If your truck is a MY '68, why does it have the 3-line fuel system? Those emission protocols came in later than '68.
And if your truck has 5/16'' fuel connections [and CS in the VIN] it was originally an L6 truck.

I had a Holley fuel pressure regulator inline before the carb [Carter AFB 9635S 600 CFM] on my 350 in a '71 GMC Jimmy... I dialed it in to 5.5 PSI with a pressure gauge [then removed the gauge]. A few years later, I got a mechanic to troubleshoot why I had power issues. He looked at the regulator and said, ''Well, you don't need that,'' and we took it off. Ran fine ever since.

The L6 fuel pump is a different animal. Forget about using one on a V8.
L6 fuel pumps operate with the flat part up. V8 pumps are flat part down.
The actuator arm meets the cam directly on the L6. On a V8 there's short pushrod that links the cam to the pump arm.

Re: New fuel pump= flooding and gas every whare.
 

I think it's likely if you get a stock type fuel pump from a store other than NAPA for a 1970 or earlier Chevy with a 4BBL 350 engine, it will have the right pressure to work with a Quadrajet. Here's one a Jegs that says it is 5 PSI. The part number is 117-MF0001. I imagine (but admit I don't know) it is the same part Autozone lists as AMF0001.
https://www.jegs.com/i/Delphi/117/MF0001/10002/-1
I don't know what to think of NAPA. When I go to the 2 links you provided and click the link to check vehicle fitment, for both the 5.5 PSI and the 9 PSI fuel pump say it does not work on a 1970 Chevy C10 pickup.

Edit: It could be a 5 PSI fuel pump would still give you problems that appear to be pressure related if your carburetor is having a problem with the needle and seat and float.

Re: New fuel pump= flooding and gas every whare.
 

That AMF0001 looks like a great candidate. Thanks for finding that. Although Autozone says it doesn’t match the ‘81 g30 350 engine I have in the ‘68 C10.

I’m going to go with regulator approach. It should eliminate the risk of a the rated pump value not being accurate. If the new 3 line pump already on the truck prematurely dies then I’ll try the AMF0001. After shutting down the engine, the pressure quickly drops to about 6psi so I think that’s the limit for my carb.

That 5.5psi at NAPA did have a different lever, so was a non-starter (see picture).

Re: New fuel pump= flooding and gas every whare.
 

Closing my fuel pump problem. It turns out my random dying wasn’t fuel fuel related at all. I won’t go into all the incorrect rabbit holes I went down to find the problem, but it turned out that the new Summit HEI distributor ignition module was bad. I replaced with AC Delco and am confident the random dying is history.