Plain old Polaris blue, non-synthetic at 40:1. Never a problem, and fewer deposits.

 

i've used 3 cylinders 400 scrammy the last year,all using klotz
50:1 regular techniplate,it is the lowest synthetic stuff offer and
it work just fine in those low revving engines,i was pretty amazed the
last jug opened with,pistons,and cylinder wall were in really fine shape,
just a little oil deposit on the exhaust side where the flange go out,
but that just normal day running exhaust have spit alot of fume then...
just a carb cleaner shoot spray on it and it is gone,no stick for sure.
even i use energy release metal conditioner in all my oil quarts,mixed through the oil than mix through the gas,and i use octane boost a lot,,,
no single severe carbon build up problems.