i have been having the same problem with my 75. it seems that ihave this one spark plug that will make the the cylinder fire on that side but the other side wont. switch that plug to the other side and same thing. im also getting lots of oil from pipes. ive had all new plugs and still does this. how did you fix yours? any help would be greatly appreciated. and if you didnt fix yours then i guess we are in the same boat