my 75 hp johnson electric shift was running great . the boat it was on wasnt much good so after i had it running good i moved it to a better boat .it ran ok after the switch in tank i was going to lake to test it today and now it wont start. it started for a few mins. then kind of sputtered and died now it wont start at all it just back fires some and nothing else. it does have spark on all four pluggs . I cleaned them and put them back in.I tried again with the same results. They were kind of dirty the first time .I pulled them a second time after i tried to start they seemed clean with just a little fuel on them. thanks for any help.