Walbro WT-813 high-performance carburettor. This is the carburettor recommended by Zenoah for upgrading your RC-style engine. Engines with the standard carburettor (WT-603, WT-668, etc) tend to experience a lag in low-end acceleration when tuned for peak power. The new carburettor includes an internal acceleration pump to allow faster recovery as throttle increases. Carburettor specs: Walbro WT-813. 15.88mm bore, 12.7mm venturi, independent tunable high and low speed jets. This carburattor does not have an internal choke.