:idea: Its most likely the single idle jet of the 5200 or 32/36 Weber carb. Lopsided idle mixture uneven to all six cylinders, and very poor economy because of the idle circuit not feeding the engine makes a huge lean igntion issue which people try to prop up with other jetting changes.
Primary and secondary need to be partly open for air flow, and always, low speed pre-ignition is realted to the one jet, six cylinders feeding issue. About 13 version of the 5200 exist, and 28 of the 32/36 Weber. Its hard to be general with these carbs. The trick is to reprofile the idle jet, and secondary opening to ensure no knocking.
I had so much trouble with my C3 AUTO, 32/36 1975 TD Ford Cortina 2000, which had a Pinto OHC 2 liter engine with this carb...it drove me nutts with is incessant lean pre-ignition. Once it was set up wit extra secondary carb opening, it was fine. It was an ovebored, reconditioned OVERBORED high compression 2000 GT 9.2:1 car with an orginally manual spec ignItion and carb, plonked into an automatic low stall ratio car, so idle postion of the secondary blade of the throttle was critical.
Don't use any aftermarket air cleaner unless it works. Any toime you Cheap out on a Carb or Ignition, you ensure a whole pile of problems.