I'm trying this one again now that the dust seems to have settled with the forum upgrade.
I'm fishing for ideas and feedback on the problem described below. About 2 weeks ago, I started noticing a drop in power cruising on the highway - it manifested as I slowly accelerated to pass traffic in a 4-lane highway. RPM dropped to around 2500, it felt almost like I was running out of gas, then recovered after a few seconds.
It seems to be load related. I can manually drop into 2nd, push the car up to around 4000 RPM or better, and if I hold that a bit, the same thing occurs.
I can run the car up to 3700-3900 RPM in park and it revs just fine. Take the car on the road accelerate to 3000-3200 in drive, and it wants to fall on its face.
I have gone over the fuel delivery from end to end. I swapped carbs with a spare, replaced all the old rubber (most of it was not really old, but it was cheap), replaced the stock pump with a stock replacement (only $20 and was not sure hold the pump was anyway), checked the hard lines, replaced the filter, and pulled the sending unit (it was clean, the PO had replaced both tank and sender a few years ago).
I tried a new coil, temporarily swapped in a replacement Pertronix module, and both checked/re-gapped my plugs to .035, then just for ***** and giggles, replaced them (yes, checked the gap first). I made sure my timing did not change (I run around 14 degrees initial, all in @ 35/36 @ 2800). Vacuum adds about another 10-12 degrees,an have always run it off manifold vacuum.
I pulled the valve covers and did find some evidence that some valves are rotating as if insufficient seat pressure. I changed springs to a little stiffer set, seat pressures is close to 125 installed.
I road-tested after each change and found that nothing actually had any effect on the symptoms whatsoever.
Last night I realized I had not looked at the radiator fluid, and found it was a little low -I am not sure it's related, but now wondering if I have a small head gasket leak. The car has not overheated. There is no evidence of any coolant leaks, and oil level is normal. No evidence of oil/coolant mixing anywhere. If it is a leak, it has to be coolant leaking into a cylinder and small so it doesn't effect performance at low RPM (below 2500).
When putting a vac gauge on the motor, Idle vacuum holds steady at 16 Hg, which I think is to be expected with my cam profile, and I see no unusual behavior suggesting valve float when revving up to 3700 RPM, or evidence of worn rings or other head/valve wear.
What I have not done: When cranking w/out the coil hooked up,the car sounds like cylinder compression is even, but I have not checked actual numbers. I am not sure that a small head gasket leak would show up in that kind of crude check anyway. I have not changed plug wires.
Any additional forum thoughts on this? It's driving me nuts,and my wife really wants me to focus on finishing our deck vs messing with this an old car. I'm too OCD to let it go, so before I either pull the heads myself, or take this to a mechanic and let him deal with it, I'm looking for any ideas to help narrow my options down
If this looks familiar, I started the same thread just before the forum upgrade,and my thread disappeared - right as I started troubleshooting, so that was frustrating in and of itself.