Join Date: Oct 2011
Location: Corona De Tucson, AZ
OK... I'm not sure what an "air screw" on a Mikuni carb is........ but if you mean pilot mixture screws...turning out=more fuel=richer mixture.
Directly from the Mikuni tuning guide...
"Why This (normally) Happens:
1) When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system.
2) The combined effect of the closed throttle and elevated engine rpm is to create a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat.
3) Under these conditions the pilot (idle) system cannot deliver enough fuel to create a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there.
4) When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected ---- the exhaust then pops or backfires."
Sick Mick* 2006 V Star 1100 Custom
--- Striping, lettering and paint by Sick Mick 6* Tree - 2" extended forks 21" front wheel - HK Sideburners - Progressive rear shock Pods Sick Mick solenoid delete - Spring seat - and other stuff
Last edited by Sick Mick; 10-09-2014 at 09:21 AM.