Did you replace only one coil? What about the points and condensers?

Have you checked compression?
Dave

After reading your post again, since you had it running great at first, I’d first check your points adjustment again and if that doesn’t fix it, go back into the carb and look for any small fleck of dirt, and spray carb cleaner through all passages again with needle valves removed. With new gas lines, I’d be suspicious of small rubber fragments shaved loose when pushing gas lines onto mating nipples. This can happen downstream of the filter. That bit me twice this summer.
Dave

Until proven otherwise, I suspect it is ingesting water into a cylinder.

Did you use a Sierra carb kit along with Sierra points? Both are terrible, and could cause your symptoms. i made the mistake of trying Sierra points a few yrs. ago, mainly because I can by them dirt cheap. I found them to be of terrible quality, and went right back to OEM. Same goes for the carb kit, that does not come with a new float from Sierra.
Is your motor running a single line hose with a fuel pump? If so, and if you are using an aftermarket fuel line and bulb from Wal mart, or whatever, that will eventually be an issue. The inner barrier liner in those aftermarket fuel line will eventually come loose and clog the line shut. I’ve had to replace a truck load of those things. The motor will start and run for a short distance, then slow down and eventually stall out. Just a few things you may want to consider. Hope this may be of help.