Picked up a 782last year that ran--barely. Made a dedicated sprayer machine out of it. Works great but we can't get it to run perfect. Darn thing surges, sometimes a lot, sometimes at all throttle speeds. Here is what has been done.
New plugs, all fuel line new, removed and washed tank (great flow to pump). By the manual, we adjusted the governor (the pc that clamps to the shaft).
Opened the carb up 3x's at least. Removed the 2 large welch plugs (that's all was in the kit). Last time I drilled out one of the small brass plugs so I could visually see I could poke a wire thru the small brass vertical tube (air supply?) that feeds into the main jet area. I blew so much air (non-osha approved air gun) that I blew one of the welch plugs out. This is a Walbro carb, only adjustment is the low idle. Start by the book, sometimes run it in 1/2, sometimes open it 3 turns----sometimes it help, sometimes it doesn't. After I put the carb back on yesterday it ran great, tweaked jet 1/4, backed outside and let run for 10 flawless minutes. Decided to drive it around over some rough/hilly ground. Sure enough after a couple minutes the surge was back. We tweaked the carb, shortened the fuel line so it would barely touch the block (thinking heat/boiling fuel), problem still inconsistent. It actually started surging on one test run and the second we raised the hood, it quit.
I did notice 3or 4 tiny black specs in the fuel bowl at one point yesterday--thinking something is coming loose from the pump (lines are new) Filled the tank fairly full, bypassed the pump, and added an inline filter. Her is how it behaves now, the first few minutes, it runs rough, now once it is hot it runs well enough that I logged about 2 hours running yesterday. Honestly, the only thing I know to do is pick up one of those aftermarket carbs and a fuel pump. Our theory is trash is coming from somewhere and intermittently obstructing something. We have yet to find a bunch of trash or varnish anywhere in the fuel system, and the fuel pump was swaped out for a used one I replaced on a M18 that got lots of new parts.
Are we missing the obvious somewhere?