The Pleated elements filters, K&N and the cheap knock offs cause excessive air flow turbulence through the carbs. This causes a weak irregular vacuum signal for the slides. This causes the slides to not lift as they should. Leaving a flat spot off idle that is very hard to tune out.
I had the K&N filters on my 75. I tried for weeks to tune it out. I heard about these issues others were having and they swapped to the foam filters to fix things. I did this and the flat spot disappeared.
Some of the cheap knock offs have a lip around the inside to locate the filter on the carb. This lip can block off the vents in the carb bell. The vents air to let air mix with the fuel at the main and pilot jets. Any restriction of air screws up the mixture.
Leo
I had the K&N filters on my 75. I tried for weeks to tune it out. I heard about these issues others were having and they swapped to the foam filters to fix things. I did this and the flat spot disappeared.
Some of the cheap knock offs have a lip around the inside to locate the filter on the carb. This lip can block off the vents in the carb bell. The vents air to let air mix with the fuel at the main and pilot jets. Any restriction of air screws up the mixture.
Leo