PMO Idle Circuit path

[moneymanager]

Been chasing a continuously clogging idle circuit for a couple of weeks now. The car runs beautifully for a few minutes then goes to four or five cylinders at lower rpm. This is the second time this has happened in about ten years, each time after I stirred up a bit of sediment or something while changing a float bowl control valve.
For the record, I have good fuel pressure, perfectly adjusted float levels, new 'O' rings, new fuel filters, a three year old Fuel Safe and unfouled plugs.
When the clog first occurred, I blew out the idle jets and pushed gumout thru from the idle air openings at the top with the motor running. The car then ran beautifully for five minutes then clogged again on another cylinder. After doing this more than ten times I pulled both carbs, disassembled, and blew gumout and air thru every passage I could access. At that point the motor ran perfectly for 2 hours then clogged again!
My current theory is that the problem may be caused by deterioration inside a ten year old 4" rubber hose just at the carb after the fuel filter. When I get the car back in my hands I'll check that.
I think I understand where all the relevant passages are in the PMOs but wanted to ask the experts.
My understanding is that gas leaves the bottom of the float bowl, is pulled up a dedicated passage to the top where it is mixed with air then sent thru the idle jet back down another passage to an orifice into the venturi, passing the progression circuit along the way. Can anyone tell me if I am missing a passage that could somehow contribute to my problem?
I've had lots of help from earlier threads on this topic, especially including this one:
5 cylinder stumble crossroads - continuous saga of plugged idle jets.
Paul Abbot's many comments have also been most helpful.
Jim

[1QuickS]

Hi Jim,

All carbs (that I am aware of) have the fuel for the idle/progression circuit drawn from the emulsion tube well through a dedicated and parallel fuel passageway as you described. Air is mixed with the fuel in the idle jet and then is drawn into the progression fuel gallery.

Have you cleaned only the idle jet to correct your issue? Try pulling the idle jets, one at a time and separate the jet from the carrier and look through the jet at a bright light source to see if there is a blockage at the tip. The smallest hole in your carb is the one in the tip of the idle jet except for the hole in the tip of the accelerator squirter.

Be sure your air cleaner is in good condition and the gaskets sealing it are compliant AND reliably sealing around their perimeter. I use a strip of neoprene foam gasket on each surface of my K&N air cleaner elements to assure there are no air leaks there.

I suffered a reoccurring idle jet blockage issue years ago and found it to be due to a rusted trough in my air cleaner housing where the sealing gasket went. Air would bleed through the rusty hole, bypassing the air cleaner and deliver rust flakes to my #3 idle jet. The rust flakes entered my carb either through the emulsion tube (most likely) or through the vent pipe in the top cover.

Rubber hose deterioration may be the culprit. PMO carbs do not have the little fuel screens around the banjo bolts (not really necessary) so hose deterioration between your fuel filter and your float bowl could be the problem. You could install a small fuel filter ahead of each fuel rail on the PMOs to catch any debris before entering the float bowls.

Check to see if you can determine the material in the tip of your idle jet next time a cylinder quits.

Or...get a larger engine that needs larger idle jets.

[moneymanager]

Thanks Paul. Bigger engine may be the best idea.
I've checked everything you mention and all seems good. K&N's are in good order with no rust anywhere. Only once during my several cleanings did I see anything on the idle jet...appeared to be black rubber I thought might be from an 'O' ring but as I think of it now it could have been coming from the rubber hose. I should have the car in my hands in the next hour or two and will pull the suspect rubber hose to check.
Thanks for confirming my understanding of the basics.
Do you have a favorite fuel filter I might consider in lieu of the clear plastic units I've been using?

[1QuickS]

I have a big CIS filter behind and below driver's side passenger seat bucket (near torsion tube). There is a length of hose that runs to both cabs and then fuel screens in my banjos. No issues for a long time. Oops, I've jinxed myself.