u/AggressiveCicada_915

95 4.3 vortec carb engine, had to swap blocks cause the last boat owners didn’t winterize correctly. Got it all back together with the mercruiser upper half and can’t get it to fire. Thought I got timing correct and distributor pointed at 1 when at tdc but all I’m getting is backfires on crank. It sat for a good bit so do I start with carb rebuild, timing, or did I do something interal wrong. Any advice helps. Thanks