2001 Rubicon 500 question

I have a 2001 Rubicon 500 and is really good shape for age and low hours. I don’t use it much. The question I have it runs well but only on reserve it won’t stay running when you turn the dial to ON. If someone is familiar with this 4×4 I would appreciate any help you can offer.

Thank you very much.

Old timer that doesn’t know to much. Lol