Replacement Body Overview - YSS5119
The YS Engine YSS5119 carburetor body is supplied as a service replacement for the 91ST carburetor family used on RC nitro engines. The description covers what the part does, key checks when fitting it, and how it supports routine tuning and servicing while not claiming compatibility beyond the 91ST label in the product name.
Role and function: this body houses the throttle slide and mixture passages and provides the mechanical interface for the carburetor needle and throttle. Swapping the body is commonly performed when the original is corroded, cracked, or when matching spares for an engine rebuild. As a replacement accessory, it only affects airflow behavior within the assembled carburetor and does not alter the engine's core design.
Installation notes: verify all mating surfaces, replace or inspect O-rings and gaskets, and confirm the needle and slide fit correctly before tightening. Use the same fastener torque as before and preserve linkage geometry to avoid changing idle or throttle feel. After installation, run the normal tuning routine: set idle, verify mid-range response, and adjust top-end as required for your engine and fuel combination.
Tuning and maintenance considerations: this replacement is a maintenance item used when wear or damage is found. It does not itself tune the engine — it restores the housing so you can re-establish baseline settings and then trim mixture and high-speed jetting as needed. Always test the engine safely after any carburetor service.
Fit this body to return a 91ST carburetor to service condition, follow established RC nitro maintenance practices, and confirm settings after installation.
