Help needed from the engine Guru’s

[Merbesfield]

I need help! Tried so many things and none have fixed my problem. 1984 SN 2001, 351W. When we idle for a long time and then power up the engine sputters and backfires horribly. It sounds like a backfire at carb. tho I’m not positive what it is. Things I have done to chase this issue.
1. Replaced plugs and wires.
2. Replaced Pertronix setup, including new matching coil.
3. Rebuilt Holly carburetor.
No change. Always seems to do this after long idles. Like out of wake zone or a cocktail cruise. The problem does clear itself after a while at full throttle, but not 100%.
HELP! TIA, Mark

[Jonny Quest]

Check your timing. You should be at 10 degrees BTDC at idle and 32 to 34 degrees at 3,000 RPMs. Also, your carb may be leaking fuel causing a very rich situation while idling. Just because you have a rebuild carb, doesn't mean it's operating at peak performance.

JQ

[Merbesfield]

Quote removed by Admin for not following the Guidelines for Quoting Previous Posts in a Thread.

Hi Jonny, thanks for helping. I don't think it is the carb. because the problem was present before and after the carb. rebuild. It was also rebuilt by a very well respected specialist. As for the timing, that I am not sure of. I have never done a timing check before personally. I will say that the mechanic who did the wires, plugs etc. should have checked it because that was the reason he had the boat at his shop in the first place. However, he was also the mechanic that couldn't fix the problem. I think I have a timing light at my shop that one of my old mechanics left. I will see if it works and watch a YouTube video on how to. What else besides the timing could I check?

[gary s]

When you go to check timing check to see if your distributor advance is working as well. After you set the timing at idle give it throttle and see if timing changes. Springs in the distributor could be broke or mechanism could be rusty from neglect.