350 mechanical fuel pump mod?

I have a warmed over 350 in my 68. finally in the 13s and im having some choking out problems at the top end (2-3 shift at about 4500+rpm) it will choke and nose over then recover if i get off it for a sec or so. No issues on launch or high RPM at the 1-2 shift, only at the back end. It doesnt happen every run, maybe every other run, and possibly when its warmer than usual. ran great, returned for a sec run and choked, happened twice so i called it a night. I'm wondering if my fuel delivery (all stock) is insufficient. Im going to replace all my old rubber sections of line, but I would like to upgrade my mechanical pump as well. im not seeing any better than stock options for the 350. is there? i did hear that you can use a performance pump for a pontiac (carter m6907 or M6122?) and switch out the pump arm for the buick. Anyone know if this is true? I've yet to disassemble a mech pump and have no idea how to remove the arm if so. my question is, can it (should it) be done? and how does the arm come off?
the carb is an excellent running qjet built by Mark Northcutt @ quadrajetpower and have never had an issue before the engine was rebuilt. i do believe the idle circuit is a little lean due to the larger cam. it has #72 jets but not sure if that will affect the top end like this?

 

I guess a fuel pressure gauge would be the right way to check on this?

I don't feel like my 350 has ever been short on fuel. Unless the pump is bad or restricted, I would be very surprised to hear you need to upgrade it. I am not a racer, but I have pushed mine pretty hard and it's seen some high speeds (especially when I was younger).

I think the Carb is a likely candidate based on your description... Assuming the fuel delivery system is good(tank, sock, lines, pump and filter.

 

Buy a pump from “rob mc” and have him or JW swap a 350 arm onto it.

 

Sean, have you seen pretty stock 350's starve for fuel with the factory pump? Just curious...

 

I can't imagine why a stock pump can't get you into the 13's consistently but the heat can be a factor. I agree with getting a fuel pressure gauge temporarily mounted on the cowl while you test it out. If you could find some kind of HP mechanical pump for a 231 V6 that would work. Otherwise I'd just install a pusher electric by the tank and that is all you'll need. My 455 Stage 1 pump by itself got me into the 11's in my '69 on a nice day but seems to be having a hard time keeping up on a hot day at the track so I added a pusher electric. I haven't tried it yet but I'm sure it will deliver plenty of fuel now.

 

I would also pull the fuel tank the fuel sock is likely plugged.

It’s likely not stock if it’s running 13s

 

Its not stock. I never had the issue running the same fuel delivery/carb before the motor was rebuilt and running low 14s with just a crower3 cam and large valves. now I have an even larger custom cam, slightly higher compression .030 0ver, TA intake. Same carb, same fuel delivery and now 13s im having these issues. So i assumed somewhere the fuel isnt keeping up. im still pretty novice at this so im open to any experienced suggestions.

I do plan to drop the tank and check. also going to change out all the rubber lines as ive owned this car for 26+yrs and never changed them.

 

Yeah i didnt even notice i had the issue until i went to the track. I run it hard on the street and runs great but rarely keep it full WOT all the way up to 2-3 shift which is too fast for these streets around here. got to the track and pushed it and it happens every other run or so.
I am going to check the tank, pickup, and all rubber lines. maybe the old lines are soft and collapsing?

 

Like I said the Rob MC Mechanical pump can be converted for a 350.

 

thanks Sean, Yeah Mark Demko mentioned to me thats what he runs on his SBB. I checked it out.. man thats a Pretty hefty price for a FP, im sure its worth it! but im trying to keep my budget under control and hoping for a less expensive solution LOL. But if thats my best option i'll make it happen

 

Exactly what I was thinking. I'd start there & replacing all the pieces of rubber line as they could be collapsing.

 

yes you may or may not need that much pump. You can also add an electric helper pump
As well.

 

Ok tank down. little 6" rubber line from the sending unit to the metal line outside the tank feels pretty soft. that will be replaced. pulled the sending unit and the sock (black) (assuming original) didnt appear to have any debris on it but it was brittle and had a split in it. i easily tore it off. now to find a new sending unit. Since the tank is down, now i can focus on the leaking filler neck. Car was bumped in the rear years ago and ever since the neck has a seepage around it. not a dripping leak but a slight moisture seep around the filler neck and tank mating area. i dont want to buy a new tank+shipping if this can be easily repaired

 

Havent had a chance to run at the track yet, will this weekend. But I plumbed in a fuel pressure gauge right at the carb inlet temporarily to check PSI, its reading 3-4psi. what should a mechanical pump serve the Qjet? i always thought it should be closer to 5-6PSI ?? New pickup, new rubber lines, original hard lines. stock type mechanical pump. from the pump to the carb is a nylon braided fuel lineto a cheapy Summit reusable inline filter (40micron, 130gph flow) fuel pressure gauge fitting to the carb inlet (no inlet filter) should the pressure be that low? or is that ok.

 

I would do the Rob mac fuel pump or the pickup he sells it is some good stuff. I use a Mallory 140 elec fuel pump been good for 15 years now rebuilt it once. No more fuel problems.