First, I SUCK at diagnostics. Been wrenching/reading for decades, but I’m just not smart enough to do much more than replace parts until the problem goes away or gets better. But I’m out of ideas here.
My car is a ‘67 Dart, 273 (former 2bbl) auto, stock aside from an SP-2P intake, 500 cfm AVS2 carb, Pertronix converted/Halifaxhops-recurved distributor. Was running absolutely FLAWLESSLY and strong, aside from the fact that it ran hot (200-210 degrees), and very slowly lost water fm the cooling system over time (even w/a coolant recovery bottle). Oh, and it wouldn’t rev beyond about 3500, which I figured was the tiny intake, but more on that later. Saw a few bubbles little in the radiator, top hose usually felt ready to burst. So I assumed one or both head gaskets were compromised, and decided to check the heads for warpage. During teardown, found a few spots of greenish corrosion on the block at the corners where it meets the heads, and figured I was on the right track.
Checked the heads, slid a .005 feeler gauge in a few spots. Took them to the machine shop. They confirmed warpage, and took .008 off to clean it up. Also did a valve job and replaced the valve springs (which were under 50 lbs! That explained the unwillingness to rev, but the car is a cruiser, so I hadn’t really missed it).
Got a pair of the “good” 1008 Fel-Pro head gaskets, put everything back together, torqued everything to spec, adjusted the valves cold/loose for initial start-up, got the engine started, adjusted the valves hot, got the timing set at 16 degrees (same as before). (Distributor did come out to access the rear intake bolts, but went back in the same orientation pointing the same direction).
Runs rough now. Backfires/pops sporadically at idle, and WAY worse when driven. #8 and #6 don’t seem to be firing. If I pull those plug wires, there’s no change. I confirmed spark from those wires, and even replaced the plugs w/new ones I had. Temp gun says #8 is 100 degrees less than the others. I replaced the distributer cap and rotor with new Bluestreak parts, and the plug wires are Taylor Spiro-Pro’s purchased a few years ago.
I feel like the backfiring is probably a huge red flag/clue to smarter folks than me, but I can’t figure it out what it means.
(Oh, and to top it all off? The temp still sits comfortably at 200-210 with a 180 thermostat. But at this point, I’m not focused on the temp at all. I just want it to run like it did before teardown so I can drive it with my son.)
It’s got 60 psi of oil pressure. Haven’t done a compression test, since it ran SO well prior to the teardown, but the rockers are all rockin’, the pushrods are rotating, and the valves adjusted fine (not my first rodeo there). I’m at a loss.
What am I missing? Thanks for enduring this novel and any ideas — I wanted to make sure I provided all relevant info.