What was once a standard one turn setting for both the idle and high speed needle on our diaphragm carburetors has evolved somewhat over the years. With the emphasis on more lean and clean running engines, our carburetors are required to meet standard parameters. These leaner and cleaner engine requirements have required calibration changes that affect idle and high speed needle tips, finer threads, tighter tolerances to gaskets and diaphragms. Needle settings can now range between 1 ¼ turns to 4 turns open after seating.
The procedure has always been that Walbro pre set the needles to a specific needle setting before they leave our factory for the OE manufacturer. Once the engine manufacturer gets the carburetors, they in turn fine tune the carburetor to meet the final engine performance specification. Therefore, it’s not feasible for Walbro to know or publish suggested needle settings. The best suggestion today is for the dealer or technician to review the engine service manual or contact the engine manufacturer for the specific needle settings. Due to EPA and C.A.R.B regulations, the adjustment needles on many of our carburetors are not easily accessible because of the limiter caps placed over the needles or the needle head profile. EPA and C.A.R.B. regulations require that any tools for adjustments be made available by the engine manufacturer and not by Walbro.