Hi- I have a scag STHM with a 25 hp kohler on it and a scag snowblower. works awsome..for 3-5 minutes, then seems to start to cut out..or run on one cylinder? runs fairly smooth but only after I take the load off. I thought I cured this problem earlier in summer when I re-set valve gaps and put two new coils on. but problem returns after running a bit? also back-fired once and shot flame out when I shut it off? any ideas would be great help. Merry Christmas all- Gene p.s. not super good starting either..but not bad.