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K&N filter options for 39mm FCRs need advice

Joined
Jun 30, 2025
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5
I snagged a project bike a while ago that came with 39mm Keihin FCR carbs. The pod filters it had were cheapos and are already falling apart. They're oval-shaped, fit weird, and split open after struggling to tune them.

I want to swap them out for some good K&Ns, but I'd like round ones this time. Should be easier to take off and look cleaner. The thing is, I didn't get any sizes or part numbers, and I haven't measured the carb openings yet.

Anyone running K&Ns on 39mm FCRs? I'd appreciate any recommendations on what size or model worked for you.
 
Try K&N RU-0210, its round, fits the 55mm carb opening well and holds up way better than the cheap pods. Measure your carb to be sure, but that one's a solid go to and looks a lot cleaner too.
 
Cool setup! I've got a 1974 Norton Commando 850 with 39mm Keihin FCR carbs, and I had trouble with pod filters too. I switched to K&N RC-1250 round ones, they fit well and look much nicer. Just measure the outside of your carb openings first to be sure. A bit of silicone grease makes them easier to slide on and helps seal them tight.
 
39mm FCRs usually take K&Ns with a 55mm ID, you see people run the RU-0210 or similar round style, fits clean and way better than the cheap pods
 
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