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This bogging has to be fuel, right?

Ok. Let’s restart. Because it’s going to get weird. This IS a timing issue. And here’s the mystery.

Set timing to 10-12 BTDC. Rev car. Or drive. Check again. Timing has retarded another 10-20 degrees.

Set timing at TDC. Rev car. Check again. Timing has NOT changed.

Do this all again. Same results. For some reason when setting the timing to the correct position once everything is buttoned down and the motor is used it slips back. But not at more advanced setting.

My brain hurts.
 
Try to set the initial timing to 14-16 degrees with the vacuum advance plugged.
That's what I am doing now. I tried it with the vacuum advance plugged off and deleted but nothing good happened.
 
Wether the vacuum advanced is used at all, used during time setting, or only plugged in afterward has no effect.

Distributor is NOT slipping.

No matter where I set it it retards 20 degrees after use. A couple of times is crept back up to the timing I set. I’m leaning toward something on the carb opening and not shutting properly. Since my tach is not functional (RT will not answer emails even after I purchased a board) I can’t verify anything regarding RPM.

Just to update the setup: 383.
MSD 6A. Edelbrock AVS2 650. New Edelbrock coil. Mag pickup in old blue cap distributor. New V belt and plugs.
 
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solved.

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NOT SOLVED! New cap and rotor. Timed. Drive. Now ADVANCED 5 degrees. It runs.... I give up for now. At least that thrum thrum thrum sound at cruising speeds is gone.
 
1970 SuperBee 383 (20k miles on rebuild), brand new Edelbrock AVS2 650 (vacuum advance), brand new Vapor Separator w/ return line (from the good company I cannot recall the name), all new rubber, vented gas cap.

Bogging down under load. Mostly when shifting into 4th and stepping on it. I can finesse the pedal to drive fine otherwise. But it got REALLY bad going up a steep incline in third and second, which has never happened before. The only major thing I have done to the car recently is installed fresh plugs and set the timing as it was heavily advanced.

One weird aspect of this car is that it is a 383 with a return line. But it's worse. The return line delivers into one of the vent lines. And the return nipple on the sending unit where it is supposed to run is crimped shut and useless. I do not know why this was done. This is why I use the vented gas cap, as pressure was building up and causing fuel seeping from the vent lines between the metal and the hose under the car. Yes, I want to put in a new sending unit and correct this but it's a messy job I have been avoiding as I do not have access to a lift.

So this bogging has to be fuel related, right? But what to do? Try deleting the return line and trying again? Run some seafoam through the tank just because?
 
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