If the best position is as much as three turns open, the jet is to big.Correct carburetor jetting is important for proper combustion. Retest with a larger size. If the position of best idle is less than 1/2 turn open, the idle or pilot jet is too small. Screwing the screws in enrichens idle, and vice versa. On Mikuni carbs, the idle screw controls the flow of air, bled into the idle fuel flow.
When exhaust gas temperature is optimum, 1250-1275 degrees F, the spark plug insulator will be a light tan color. The optimum air fuel ratio is 15:1 for gasoline. If air flow is enhanced, fuel flow must be adjusted accordingly.
Mikuni Jetting Guide Manual If You
Carb Jetting Guidelines - Just a ballpark range based on years of customer feedback and personal experience. It's worth it's weight in gold. Other factors requiring jetting adjustments are changes in air density, altitude as well as types of fuel. Get a Sudco Mikuni tuning manual if you don't feel real comfortable with carbs. They are windows into your engine's soul. Get familiar with exhaust note changes when jetting and get used to checking your plugs often.
It doesn't take long before you're as quick as a pro & really inspires your tuning confidence. If you're new to this, it helps to practice removing your carbs and replacing your main and/or pilot jets as well as adjusting the needle clip position. Higher altitudes or humid conditions will require proportionally leaner settings. The specs above are a general range for U.S.
Position, start in the center and go from thereCylinders. If you have a similar set up you can try the jetting listed.Main jet will be between 180 and 240 Needle the same.
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