18HP Twin Vanguard, Horizontal shaft motor. Uneven surging issue

[slomo]

One thing I found out, is that this engine gets HOT fairly quickly. After about 6 minutes, I could no longer touch the valve cover.

This is why I preach on here to CLEAN YOUR COOLING FINS AND BLOCK AREAS. Also it's in your engine manual as a MUST, yearly, to-do item.