Hitchcocks Forum

Hi again. Connie is now running reasonably well but I need a little advise re carb tuning. Carb is fitted with original spec jets etc but was fitted with a stubby open bellmouth. I have fitted a similar billet item but it has a built in fine stainless mesh to stop bits going in. Does anyone out there have an opinion on any tuning tweeks that may be necessary as a result? Obviously after riding modern bikes for half a century it is difficult to establish a benchmark for 60 year old iron. Thanks in advance. Dez

It'll be fine unless you plan to blast along absolutely flat out for miles. And I suspect that you probably won't be doing that?! If anything it'll make it run fractionally richer right at the top end and might even have a beneficial effect on starting. These fine gauzes are a useful flame trap, preventing a spit back igniting the fuel which is very abundant on starting and in my experience very scary! My gloves got singed but the bike was ok I'm glad to say.

REgards, Mark

Those fine gauze mesh bell-mouths can restrict open area to the carb mouth by over 60%, and plays merry hell by creating excessive turbulence in the carb mouth and venturi; where you dont need turbulence in any carb.


I hate them with a passion as they can (do) upset clean carburetion.


Me? I'd stick with the short 'velocity' stack, without the gauze.

I would have said about 10 - 15% restriction from the gauze, myself @ full throttle, but whatever the numbers, it will richen things up to a degree. Depends where you live / ride, but the only stuff that gets sucked into my engines tends to be rain ...