OK, so I have searched the forum for an entire day, no golden nugget to fix my current issue. Here is the background, current situation and troubleshooting to date:
'73 250 shortblock 106k miles suspected rebuild, '77 head 69k miles, 6-1 header, YF carb, duraspark2 ignition running ported vacuum, fresh plugs, gapped .045", Taylor race wires, MSD blaster coil, static timing 12 degrees, new fuel pump and filter, all new gaskets and seals, dissassembled and cleaned head and valvetrain when on original shortblock (which ate #6 bearing and destroyed block). No milling or decking, stock cam and valvetrain, felpro headgasket, 10W-30 penzoil crap until she is all straightened out and make sure no leaks, 93 in the tank, stock C4.
Upon startup, she has a horrible rough idle, vibration, and my PCV valve is clicking open and closed (not caused by pressure in the valve cover), as if it is loosing vacuum or seeing pressure on the intake side. Under load, I have spuratic backfire through the intake. You can pull #4 and #6 wires without effecting the idle. Replaced the PCV valve, I verified I had good spark, even replaced the plugs, and ohmed and swapped wires. I will do a compression test tomorrow, but I did pull the plugs on each of those cylinders, put my thumb over the plug hole and did feel compression, and each felt the same as #5, but this tells me little. I pulled the valve cover, and have good lubrication the length of the rocker shaft out all orifices. Each valve and pushrod appears to be operating correctly and to the same degree as much as an eye can tell visually at idle and higher RPM. Once I put about 5+ miles on her, and then come to a stop and idle a moment, the car suddenly smooths out and she runs well at idle and load. The idle is like silk, power is restored, the PCV valve stops clicking, and the symptoms to not return until the car cools back down. If you then pull the plugwires, as before, the idle stumbles as it should. I pulled the valve cover off in this condition, and the valvetrain appears to be operating the same. I thought I likely had a stuck intake valve(s) or lifter(s) colapse, but cannot confirm this visually. There is no smoke to speak of, she runs very strong for a stock 250 when she finally quits missing. Any ideas, I am going nuts here?! I really do not think this is a carb or timing problem, and cannot confirm my suspicion of the valvetrain...
'73 250 shortblock 106k miles suspected rebuild, '77 head 69k miles, 6-1 header, YF carb, duraspark2 ignition running ported vacuum, fresh plugs, gapped .045", Taylor race wires, MSD blaster coil, static timing 12 degrees, new fuel pump and filter, all new gaskets and seals, dissassembled and cleaned head and valvetrain when on original shortblock (which ate #6 bearing and destroyed block). No milling or decking, stock cam and valvetrain, felpro headgasket, 10W-30 penzoil crap until she is all straightened out and make sure no leaks, 93 in the tank, stock C4.
Upon startup, she has a horrible rough idle, vibration, and my PCV valve is clicking open and closed (not caused by pressure in the valve cover), as if it is loosing vacuum or seeing pressure on the intake side. Under load, I have spuratic backfire through the intake. You can pull #4 and #6 wires without effecting the idle. Replaced the PCV valve, I verified I had good spark, even replaced the plugs, and ohmed and swapped wires. I will do a compression test tomorrow, but I did pull the plugs on each of those cylinders, put my thumb over the plug hole and did feel compression, and each felt the same as #5, but this tells me little. I pulled the valve cover, and have good lubrication the length of the rocker shaft out all orifices. Each valve and pushrod appears to be operating correctly and to the same degree as much as an eye can tell visually at idle and higher RPM. Once I put about 5+ miles on her, and then come to a stop and idle a moment, the car suddenly smooths out and she runs well at idle and load. The idle is like silk, power is restored, the PCV valve stops clicking, and the symptoms to not return until the car cools back down. If you then pull the plugwires, as before, the idle stumbles as it should. I pulled the valve cover off in this condition, and the valvetrain appears to be operating the same. I thought I likely had a stuck intake valve(s) or lifter(s) colapse, but cannot confirm this visually. There is no smoke to speak of, she runs very strong for a stock 250 when she finally quits missing. Any ideas, I am going nuts here?! I really do not think this is a carb or timing problem, and cannot confirm my suspicion of the valvetrain...