, yeah that could be true .

 

So quick update . I was talking to a dyno guy I use now and then and he pointed out that the F3 ,in standard set up, runs on the lean side in the midrange . so any alterations like replacing the down pipes or aftermarket silencer will make the bike run even leaner. He suggested putting 1mm shims under the carb needles , to be honest you can't really put any bigger a shim under without locking the needle which would cause wear to the emulsion tube . So fitted the 1mm shims , and have to admit it is much better , very little lag and not really an issue now. I also replaced the fuel pump points as they were a bit burnt and they are cheap to buy anyway . Fingers crossed that's the motor sorted

 

Hello Paul, awesome garage line up! I was banging my head against the wall with this problem, asking these fine folks for help every week for suspected leads on this. I wanted to share what sorted mine out and see if its of any use.

So I had to find the mixture at the rev ranges so went to dyno like you rightly did. Mine was was super rich in the midrange which bogged the throttle and gave me the same headache I bet you're having! I know you said lean but it sounds like the issue is coming from the same components.

I separated my carbs and had all new O-rings and made sure they were all air/water tight, serviced my air solenoid with scotchbright and some silicone grease, as they get nasty inside with rust and general air duct filthery and they don't run very smoothly. This could be having an effect on this (seemingly) very common problem! worth a punt!

The new O-rings in the carbs and a balance have fixed 2 years of problems and mine is smooth all the way through the rev ranges and throttle positions, do a balance after and see where you're at! Think they fixed vacuum leaks from the diaphragms or just between the carb bodies. Buy some more carbs and get them on and see if it changes the way your bike runs..