OK so we have a V50/mark2. In fact we have two with the same problem.

Both bikes have had the standard air filter system removed and KN fitted. The problem is they are both running rich. On the one a friend has that I am trying to sort the carbs have been stripped and cleaned with all new jets and choke plungers with slightly bigger main jets. I can get it to run fine up to 4000rpm approx then it runs rich and cuts out.
Funniley enough a friend from Newcastle ran me today with a similar problem same set up. He says his starts from cold with no choke and runs rich. We have both been working on Guzzis for 30 years but this one is baffling any new ideas or have we both missed something obvious

I would have thought that using K&Ns you get freer flow and hence a weaker mix. I’d suggest if the bikes are high mileage then change the jets as I’m told they wear over time due to general dirt in the fuel. I did mine at about 50k miles and there was an appreciable improvement. But you’ve got new in, and I presume the right ones. Another place is the groove that you get over time in the enricher plungers, but you’ve changed those too – and I presume got plenty of slack in the operating cables for those. I ballsed mine up at the last service by somehow ending up with one of them too tight (and I’d not even adjusted them).

So far then I’ve been no help.

I’m still running mine on the original air filter set up and the std jet set, original slide and needle. Original floats but new float needles. Despite the many postings on many sites for all kinds of bikes I’ve never fooled with float heights on anything. It runs great, but often as not I can mostly start it without the chokes. If I catch it on the throttle it will run though be reluctant to pull for a min or two is all. Hence I’d always figured it was a little rich down there, but hey.

This is a timely / concerning / interesting thread for me.

Presently re-fettling a mk2. Bit of a tart with 10 previous owners!!

Decoked and heads back on today. Also cone filters arrived in post. Not K&Ns, but much cheaper alternatives. Keeping them dry. Have also got main jets 110 & 115 in jiffy bag to trial as, like cyclobutch suggests I believe “she” may need enrichment. Might just leave 105s in meantime and maybe see if I can use the Sportie Innovate lambda sensor to check actual AFR.

Usual suspects: choke plungers not closing fully; floats too high; floats holed; floats jamming on side of float chamber (swollen); air galleries blocked (for idle and needle jets mixtures); needle heights in wrong notch (too high); needle jets worn oval …

gave up with the choke system on my v35, fitted vespa style flip tops and had no problems since

K&N filters will make it lean out rather than run rich

Are the needles set properly ie middle grove? also worth checking the float height and valves