Ok, I'm about at my wits end over a problem I've been having with my '69, aka 'the Beast'.
Symptoms: Runs great, until I hammer it. Then just about the 1-2 upshift, it quits - I mean flat quits, falls on its face, nothing, nada. At first I suspected ignition, but I've managed to rule that out. It's definitely fuel related. When "it happens", if I pull over and quickly raise the hood, I can see the fuel pressure going into the carb (I have a gauge on the regulator) has all but disappeared. Instead of the carefully adjusted 6.5 psi at the regulator output port, there's 2-3 psi, maybe less, and the need is fluctuating. Whats weird is that when I start it cold, the pressure is rock solid where it's supposed to be --- and will stay that way no matter how long I let it sit idling, until I drive the car and hammer it --- then it happens again.
Fuel system, back to front:
*Factory tank, modified to move the fuel pickup to a rear sump. (I still have the factory pickup (a new one with a 1/2" outlet port that I'm not using) in the tank just for the fuel gauge sending unit, but the fuel pickup itself is blocked off.)
*From the rear sump pickup point, -8 AN braided steel (about 2 feet) to a large RobbMc cartridge filter (100 micron).
*From the filter, probably another 4 to 6 feet of -8 AN braided line routed inside the rear and side of the drivers side frame rail and along the rear suspension crossmember to approximately the point where the factory fuel line would have connected.
*At that point it connects to 1/2" stainless hard line from Inline Tube that follows the factory routing where it appears again out of the same hole in the front crossmember where the factory line would have terminated.
*From there, again we go to -8 AN braided line to the input of a RobbMc 1100 hp mechanical pump,
*From the pump, more -8 AN to another large RobbMc filter connected directly to the input of (you guessed it) a RobbMc deadhead regulator
*The regulator and filter are mounted crosswise just above the water pump. From the regulator, -6 AN to the carb.
*The regulator has a RobbMc fitting for a vapor return line (even though it's a deadhead regulator) which is connected via -4 an to the repro Inline Tube factory style return line, back along the factory routing, and connected to the factory vapor return fitting on the tank via more -4 an braided line.
What I've done so far:
Pulled apart both filters and examined their bronze elements. Both were clean inside and blowing the elements out with compressed air didn't reveal any trash in them.
Rebuilt the regulator with a fresh diaphragm even though the "old" one looked fine and didn't seem to have any leaks.
Installed a second, brand new RobbMc 1100 pump adjusted to provide about 10.5 psi on the output side.
When I've caught it "doing it" after a test run while the fuel pressure is in the basement, I've hurried around and removed the gas cap on the tank to see if it might be a venting problem ---- no change, doesn't help - pressure still low.
I guess my next move is to drop the tank, remove the sending unit assembly and see if I can find something loose inside the tank that could be finding its way to the rear fuel pickup under acceleration. It's a job I don't really want to do, but at this point like I said, I'm stumped.
I guess maybe I could completely remove the filter elements from both filters and see if that changes anything... the only things left after that are the lines themselves.
Anyone ever hear of any AN braided lines that deteriorated inside and plugged up from the ethanol content in pump gas?
Another thought I just had... wondering if having the regulator/filter mounted where I do is allowing them to pick up too much heat from the water pump? I've got them mounted with a rubber insulated strap around the body of the filter and seems like the fuel flow would tend to keep everything cool but still...