clutch safety switch

this old slant duster had last been on the road in '99 but no doubt someone had cleaned the carb (no history on the car) because at first start up it started and ran fine. ( I pulled the gas tank and put in new sender/pickup)..then it would just die after sitting and running fine in neutral. . I MASHED the clutch in and out a few times then all of a sudden start and run. like I mentioned, I am using a new starter relay that preceded the CSS nuisance. since you say the CSS is not an issue, all this is strange. I replaced the ballast.