installing distributor chevy 350 tbi intake

I have run engines in the darkness of night to spot plug wire cross-fire/grounding. The backfiring makes me question distributor cap, rotor button, and/or plug wires resulting in cross-firing.

A bad coil or coil not matched to the ignition system can cause poor performance, including the lost power above 1/2 throttle. You mentioned erratic spark observed with a timing light. Will cause poor performance/power but generally does not cause rough running. Regarding your issue 'motor will not start unless I give it slight throttle and then it runs like complete crap.' It sounds like your timing is now low as you have to give it throttle to start/run. So my issue is now the motor will not start unless I give it slight throttle and then it runs like complete crap. I verified that the plug wires are all in the correct firing order. Set cyl#1 at TDC compression stroke and point the rotor under the distributor cap directly at plug wire #1. So I proceeded to change the distributor. Multiple cylinders had erratic spark, almost like Morse-code looking spark. So I bought a timing light and checked spark on all cylinders. I then checked my spark plugs and they’re all black and sooty and my exhaust smells extremely rich. I cleaned the fuel system(changed filters), tanks are brand new, and I rigged up a way to check fuel pressure at outlet of fuel pump. Since I bought it, the motor has no power past half throttle(starts bogging down and backfiring through the intake). My question is about my 26’ shamrock with a 350 Chevy tbi by marine power. So I’m new to marine inboards, I’ve only ever owned boats with outboards.

Installing distributor chevy 350 tbi intake