Inside you will find the factory breakout diagram of the Satoh Bison Nikki carburetor. Note that two similar but different types of carburetors were used on the S650G over the years (Stromberg and Nikki). Valley Power has a simple illustration to help you identify which is installed on your tractor.
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To Rebuild or Not, that is the question.
If you are having trouble with clogged jets or a gummed up carburetor you may or may not need to dissasemble and rebuild your carb for best performance. Unfortunately, the gasoline of today contains ethanol which is terrible for motors that do not see daily use. The ethanol in the fuel breaks down and turns to gum and varnish quickly, even when you use fuel stabilizers such as Sea Foam or even Stabil. To prevent this in any carbureted engine you can drain the fuel from the float bowl after every use.
Before you decide to rebuild your carb you may be able to clear clogged jets without disassembling the carburetor thanks to the design of the Nikki carb. If your Satoh S650G Bison will not run without the choke partially on when warm chances are you have clogged jets. Depending on how bad your clog is you may be able to fix the issue with spray carb cleaner following these steps:
If your tractor still does not run properly but does have noticeable improvement, try the steps above again but wait longer with the carb cleaner in the carb. Otherwise removal of the carburetor and a thorough cleaning is necessary. The good news is the rebuild kits are easy to find from the links on this site, Amazon, and even Ebay. More good news is that the Nikki carb is not difficult to work on.