You are sooo correct, it was a 33m677 and I replaced it with a 33s877 so that made me confuse the numbers. I moved the oil pressure sending unit from the old eng to the new one and popped the pin out of the cable on the old to wire the new one... all is workign fine with 1 exception. On my mower and all mowers as far as I know, you have to run them at full throttle to keep the blade speed up. This new engine is acting like it has a governor set to low... when I put it at high throttle it seems to kick in and throttle it down unless I am actually loading up the mower by cutting grass. Any ideas on how to make it act like the old one? Ok I jut reread your reply, the old model was a 33m677 0123 g1, I replaced it with a 33s877 0018 g1.