Running rich

[Blue]

38’s on 1127, it seems I’m running a bit rich, there’s some black soot in the tip of the exhaust & it’s popping & banging out of the exhaust. Do you think I should lower the main jet, alter the needle or wait till I get on the dyno (should’ve been today but looks like it’s gonna be next weekend)

[Gixer1460]

Unleaded fuel makes (IMO) 'reading' mixtures via tail pipe harder than it used to be - plug colour is more reliable. Popping and banging in exhaust on over run is usually too lean. 38's will need bigger MJ's unless the engine really needs the bigger carb for airflow as a std'ish engine will have less draw on the jets so bigger mains to compensate. If it's going to the dyno - all well and good.

[Blue]

Hmm plug is black 

[nlovien]

plug condition isn't much use unless you back it up with the known operating condition at the time you cut the ignition - get her nicely warmed up - long enough to clean up any cold start effects

mark your throttle in 1/4 steps to give a rough idea of what carb circuit is primarily active ( noting that they overlap i.e. although primary, other circuits still play a part )

hold the bike at your selected 1/4 throttle position - ideally with the bike under load ( find a nice straight hill ) - hit the kill switch and stop ( thats a nice hill with a layby )

1/4 = mainly idle circuit

1/4 to 3/4  = needle jet to needle, if its rich nearer the 1/4 then possible the tube ID versus needle diameter is too big  - if its rich nearer the 3/4 then try lowering the needle  - you may also lean off a bit earlier by lowering the needle - suck n see

3/4 to wide open = main jet

it's worth trying to get these very basic steps as good as you can before the dyno so your dyno time is focussed more on fine tuning - however if your Mr dyno knows his stuff he may have a good base set up - worth asking before you go 

also give your ignition circuit a good look over - clean terminals etc.. - you don't want to waste time chasing a dodgy spark thinking its fueling - likewise ref: valve clearances

the above is very old school but the basics still stand "for direct lift carbs"