Hi any advantage replacing the air fliter on my 40 webers with a set of bell mouths or whatever u call them chheers Keith

Possiby, but air filters stop dirt,insects and small mammals being ingested by your engine

The advantage would be more air flow, especially at engine speeds determined by the length ofthe trumpets, and the disadvantage would be dust etc getting into your engine

cheers thought that might be the case

Why not do both? The bell mouths are to smooth the air flow into the intake and tune it to your selected rpm range. Get bigger filters and fit them over the top.

Worked OK for me. I'm told there is a power reduction with the filters but at £70 an hour for a rolling road I could not affort to verify it. Anyone else checked it?

Not mutually exclusive. You can have trumpets / bellmouths to improve air flow with filters. Whatever you do don't fit the course mesh filters. They don't stop the dust and fine dirt that does the damage and strange the inlet!!! Worst of both worlds.... IE a short-lived under-powered engine....

Webers absolutely need bellmouths AND filters. K+N do a DCOE filter where the ram pipes (aka velocity stacks, aka bellmouths) fit inside. Without ram pipes your 40s will perform nowhere near their potential. Airflow through the carbs will be down by a huge amount.

You could also fit sock filters which are cable-tied over the ram pipes.

^^wot he said. I know of a guy who had good old fashioned SU's. Stub stacks gave a 5% power increase, same day same RR. Almost free power. And a decent filter is a must, don't skimp, false economy. I believe K+N or ITG to be about the best. And I reckon socks are not as good as a proper filter, much smaller surface area.

Ive retained the std Kawasaki bell mouths on my bike carbs and encased the lot in a 100mm deep K&N challenger. Filter is HUGE, but i doubt there will be any air starvation.