Air filters

[Bison]

Hello folks,
Could not get the rear cylinder to run weak enough on idle, 43 pilots, even tried 40's, removed the air filters and fitted the empty air filter box, what a difference!, much better. The plugs were sooty/black before, the rear one especially.
The filters look brand new though, so here's my question, are they known for being rather restrictive, or are mine simply contaminated?. They are the correct orange/brown ones. I don't really want to run without air filters so a new set will be ordered anyhow. I checked the carb sync after removing the air filters and had to re adjust the rear carb.
Thanks,
Alan.

[Bison]

OK, to answer my own question incase anyone needs info in the future. I spoke with NLM when I ordered my new filters, they said the original filters were not very restrictive at all, not a scientific valuation perhaps but good enough for me!, these guys know what they are talking about.
Thanks,
Alan.

[3potjohn]

The amount of air to fuel used is massive so it's no wonder the filters do their job.