I missed post #15,sorry.
A bouncy mark at idle is usually a sloppy chain. Try it again, but rev it up to 2400 or better, hold the rpm steady(use a fast idle step is easiest), and check for bouncy mark.
Or just rotate ,by hand, the crank. First go CCW from the front, them CW. Rock it back and forth a few times, and feel for the slack in the chain.It's easy to feel if it's worn out.I did read that it got a new chain a year ago.
But even if it is worn out, this is not your problem.
Here's a recap;
"After 2-3 minutes of perfect idle it dies.Starts right back up."
"Right at the powerband and WOT it backfires, sputs, spudders. If I ease into it it will do...Kinda ok."
"Took it out and the same stuff... spitting spuddering, and dying on me every time i stopped. Occasional backfire."
" I pulled a plug and it looks like its been running lean.."
"Got everything buttoned up. Now the only time its cutting out is at WOT on the down shift. ...."
"Runs smooth through all gears, idles well and runs as it should until you start to get into it. It will start surging/backfiring and doesnt clear up. let off the throttle and she runs fine.... I'm about to be done with it..."
I think this summarizes it.
I believe the fuel delivery is faulty. Either the fuel level is very low, or the main circuit is faulty.There is also a small possibility of valve problems.
The fuel level could be low because the pump is bad, or it's sucking air, or the delivery circuit is restricted, or the float level is wrong. The pump should be pumping solid fuel with no air bubbles in it. On Carter BBDs like yours?, it is possible to idle that teener with the top of the carb removed. If you contemplate this, be advised that there is a tremendous risk of fire. If you do this, you will be able to see the running fuel level and be able to watch for air bubbles. The teener/BBD should idle quite happily at 600 or so.There are safer ways to check this stuff, but this is fast.IF you choose the safer way, I would firstly check all the rubber lines in the fuel delivery circuit, especially the jumper at the back. The pump likes to suck air back there. Next I would do a fuel delivery test. This involves removing the fuel line from the carb, and sending the fuel into a clear jar of at least 1 qt capacity.The engine needs to be running for this test. While the jar is filling,the hose should remain at the bottom of the jar so that you can see any air bubbles. You will fill the jar about half way, and measure the time it takes, very accurately. Then you will measure the exact amount of fuel. Then with a little math, you will convert the numbers to pints per minute, and compare that to a standard. And finally you wil need to prove that the floatlevel has been correctly set.
Now if all that is good or made to be good, and the problem persists, then you will have to prove the main circuit in the carb is clear. Since it idles, and power delivery is good except at WOT, most of the carb is working, ie. the idle/transfers and metering rods, and bleeds. But My guess would be that one or both main wells under the mainjets are restricted.Since the car has a long history of sitting, I would just go here first.
But, on the off chance that a problem is not found here in the mainwells either, I would do a leakdown test, looking for valve sealing issues.Since you mentioned bent pushrods, there is a chance that some valves are sticking, or bent, or they are in some other way not quite sealing or intermittently not sealing.I mention this lastly cuz a valve seat sealing issue usually shows up pretty clearly at idle, and on a vacuum gauge, and you mention the engine not smoothing out until 900 or so rpm.
If you know me at all, I would do all these tests in reverse order. I would do an idle vacuum test at 600rpm, then the leakdown test,then the mainwell inspection, and finally fuel delivery test.Hyup that's how I would go.
Well, I should add that a severely restricted exhaust system could present pretty much all your symptoms too. .
