Ok, i am a new member, but in process of restoring my second pony. my latest project came to me as a birthday present. In need of some tlc, but #'s matching.. it is a blessing and a nightmare at the same time.
U may have found your answer, but.. it took me 2 weeks of an hour here an hour there to get thru mine, and I am hoping this info will save someone some time for someone out there
I had very similar issues. and with no history on the vehicle i was forced to troubleshoot this one from the ground up. my symptoms where multi pointed making this one fun to work my way thru
1) step on brake, car bogs
2) step on gas car bogs
3) step on gas hard and car really hates me
4) timing unstable from rev to rev
the brake apply/vacuum leak part was a sure sign that power boost was gone (as verified with a vacuum gage when 19lbs was normal idle (i shoulda seen it here as 20lbs is my target (at my elevation), and 10lbs was when brakes where applied. so i replaced that. stabilized at 19lbs the 1lb will come in handy later). Always check the check valve as this can also be a simple problem.
symptom 1 went away.
but 2 and 3 still remained. I could not get the timing to stabilize. timing would fluctuate from 10 to 6 and all around between there (after each rev). so i replaced the distributer... (it was cracked at the stem anyhow, and ...at 70$ y not.) points, wires, plugs, coil... basic tuneup (as i said this was a car that someone literally handed me the keys and said have a ball).
no help! since i had no way to test vacuum while in gear and under load.. the guy holding the guage just could not keep up with me while i was accelerating ;-) (some of you swifter folks out there,don't try this one gets messy real quick!). vacuum good at idle (- 1lb!), no bumping or swaying of the needle in the pressure guage under gas, entire ignition system replaced ran fine while revving in park.. i even did the poor mans vacuum test (ether/starter fluid (gumout works too) sprayed around the intake and base of carb !!lightly!! while listening for increase or drop in rpm). low rpm fine, would bog/miss, and rattle at about 2000-2500rpm only while driving.
long story short....... i found my problem of all places when i was restoring behind my dash... it turns out the previous owner installed an aftermarket cruise control unit. this unit used a vacuum hose from the manifold run thru the firewall, and you guessed it, now connected to nowhere. I had a small vacuum leak (-1lb doh!)which for some reason only would cause a drop in pressure when the vacuum secondary for the 4bbl tried to open. a little hose and a small screw, and she now run's like a kitten. timing is perfect. and smooth all around. Bottom line there is no 1 test to find your acceleration problem. you need to troubleshoot logically eliminating the cheapest possibilities 1st, and pay attention to the details.
1) i advise to get a vacuum guage, they are about 15$ and the easiest way in my opinion to troubleshoot timing, ignition, and overall health of the engine for a daily driver/garage mechanic.
2) try a bunch of different tests, to get a baseline of where the engine sits. believe it or not, you can identify sticky valves, worn guides, weak springs, worn seats, vacuum leaks, timing trouble, and several other problems with this simple tool and a little patience. It is almost idiot proof. Just google vacuum guage/tester
3) test frequently during your troubleshooting.
4) warm the car up before taking readings.
6) shoot yourself for not noticing 1lb differential! i'm kidding of course.
hope this helps someone out there. my 1st time through was eye opening.