The PCV valve at the intake manifold, and the tube and cover at the Valve cover must be clean. If it is clogged it will not be able to relieve the pressure in the crankcase and vent the volatiles to the intake. This excess pressure has no other route out other than the Oil Fill Tube and then to the Crossover Tube. And then, into the carb. Check for a conical screen inside the small housing at the valve cover. If there is one there, remove it and put it on the shelf. These screens were found to be more of a problem than the one they were designed to cure. Is there a lot of oil residue in the carb throat? The PCV valve can be disassembled and serviced. If however, upon reassembly, it rattles, then the spring inside is no good. You cannot purchase the spring, nor the internal valve so you would need a NOS or good used complete one. You could try stretching the spring out a little, but I don't recommend that because too tight would cause the same problem.
For a carb to function correctly;
It must be set up correctly.
It must be clean as a hounds' tooth internally with properly sized valves and jets.
No vacuum leaks.
Float at 3/8" (+/-0)as measured, inverted, without the gasket in place. Use the shank of a 3/8" drill bit as has been suggested.
Accelerator pump travel up and down 17/64" (+/-0)
Metering rod tip .046 - .048 (for sea level operation, rod #547. For High altitude a one-step-leaner #548).
Metering rod setting 2.718" (+/-0)(special tool available from Carl Walck.)
Idle mixture nominally 1 1/2 to 2 turns out from bottom
Idle RPM 600-700
You must also have;
A properly functioning Heat Riser valve.
Fresh, clean air delivered from a well functioning Air Filter.
Fresh, filtered fuel delivered to the WO at 4 to 4 1/2 psi. I recommend a filter at the carb inlet. (The old single action mechanical fuel pump like the AC572 delivers at this level without a fuel pressure regulator. Electric pumps are problematic, to say the least.) A Solex can accept no more than 1 to 1 1/2 PSI and therefore requires a pressure regulator.
Fresh clean fuel from the tank to the pump. I recommend a filter between them.
A properly vented tank.
A properly timed and strong spark to all four plugs.
Correctly set Valves with good springs.
Did I miss anything? If any one item is not correct you will have performance problems.
