Re: 115ETL78C cyl #1 detonation, twice??
Did you do an autopsy on the portion of the carb that feeds that #1 cyl? If that cyl runs lean it will cook the piston quickly. If you have any debris in any of the jets, it will restrict fuel/oil flow to that cyl. You need to carefully inspect that carb to insure it flows fuel through all the carb passages to #1 in order to eliminate fuel flow as a contributor to your current failure. Cracked sleeves are usually a condemning factor when determining whether to reuse the block. Depending on your pictures you post, you may need to get that cyl resleeved.