Review of mower starter motor current using Owon HDS242S and Hantek CC-650 reported measurement of starter motor current in “normal” operation (ie engine starts and runs). This article reports measurement of starter motor current and battery voltage with the spark plug connectors removed, the mower is Toro MX4250 mower with the Toro (Loncin) 0.708l 18kW V-twin engine.
Above is capture of battery voltage (red) and battery current (blue) using a Hantek 1008C that was under evaluation. (The image colours were inverted for the article.)
Of particular interest is the current peaks when the system stabilises. Note that the first of each pair of peaks (Cylinder #1) appears perhaps a little higher than the other.
The most likely explanation is difference in the compression relief in the two cylinders, probably due to different exhaust valve clearances, and probably incorrect exhaust valve clearance for a least one cylinder. This engine is approaching 200h and has not had the valve lash adjusted since the factory (it is part of the book 200h service routine).
Valve lash measurement
The exhaust valves should be 0.15-0.2mm lash, and were measured within that range for one cylinder and between 0.2 and 0.25mm (Cylinder #1). This probably accounts for the difference in cranking current at compression, the compression relief is degraded by excessive valve lash.
The inlet and exhaust valves were adjusted as needed.
The tests were done on a Hantek 1008C as part of its evaluation… which led to a eBay refund of the full purchase price (inc shipping).