WALBRO WT-990 HIGH PERFORMANCE CARB CY ENGINES ZENOAH Walbro WT-990 high-performance carburetor. This is the carburetor recommended by Zenoah for upgrading your RC-style engine. Engines with the standard carburetor (WT-603, WT-668, etc) tend to experience a lag in low-end acceleration when tuned for peak power. Carburetor specs: Walbro WT-990. 15.88mm bore, 12.7mm venturi, independent tunable high and low speed jets. This carburator does not have an internal choke. Note: This carburetor now comes standard with modified throttle shaft, so it will work perfectly in most R/C applications such as HPI Baja, FG Modellsport, etc. The WT-990 Carburetor is the same as the WT-813 WITHOUT an internal acceleration pump.