☆☆☆Honda TRX350D HELP ☆☆☆

☆☆☆ please help 1987 honda trx350d ☆☆☆
i have a honda trx350d and im the third owner. The quad is in pristine condition. The quad starts and runs like a champ and purrs like a kitten for like 20 minutes straight and then shuts completely off. Sometimes it will start back up after a few seconds or sometimes it takes awhile to get it started again. Originally thought it was a carb issue. Was told it had a brand new carb on it from previous owner. Took carb apart to clean and everything was clean as a whistle and new inside of it. Reinstalled and got atv running again then shut back off and couldn’t get started again. Since then i have replaced the fuel pump with a brand new one and still the same problem. At this point im not sure what to do. It does have spark i checked that as well. At a loss at this point and need help, please. Thank you in advance pete……..