I think your weight will only limit certain positions.
However, hygiene might be a factor. Obese people sweat in their fat layers and without proper « breathing », it can smell sour mostly during the summer. Weight can also impact your gut bacteria and make you have foul odor in your mouth. I am not saying that this is absolutly the case, but it is a possibility.
I read in a lot of thread clients complained about being refused a DFK. If your partner’s mouth smells terrible, it doesn’t matter you are a man or a woman, you don’t want to kiss them. Sometime, mouthwash will do the job for 5-10min but the odors in your guts will come up again afterward.
As a client, I think the minimum I can do is to have a good attitude, good hygiene and I will be given a great time.