Engine problem - '85 Mercruiser 170

[scook]

I'll do some oil sniffing. Probably should change the fuel water separator filter to be sure it's not water (the tank is full so shouldn't be condensing moisture). I wouldn't think it would start and run great for 20 minutes if the carb was clogged up - this is the second time it's done this. Was leaning toward ignition since it's the only thing that's changed but will work the fuel issues first.

Thanks