OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Scott Bonnar Original Engine - Rebuild or Replace?

OK, we have a 130 cc engine made on 15 September 1980. (Your mower was probably made just a few months later.) It is a first-series vacuum carburetor engine with horizontal crankshaft, plain main bearings and a rewind starter. It has breaker-point ignition. It has a Chok-A-Matic carburetor, and in your picture the choke is applied, so it may be maladjusted, causing seriously over-rich mixture.

Now, is the smoke it emits black (petrol) or blue (oil)? If it is black, we can start by focusing on your choke mechanism. If it is blue, we need to look at your breather system.