April, I am sorry for the delay in response, I had some technical issues at this end. In response to your question, too much pumpkin can actually cause diarrhea. This is what you can do:
1- Do not give things like Pepto Bismol or Imodium.
2- No food or water for 8-12 hours, need to give his gastrointestinal tract time to rest. Then, offer a small amount of water followed by a diet of rice (75%) and boiled boneless chicken or ground beef (25%) until the stool is back to normal then wean him back into his regular diet.
3- Supplement with a probiotic, these are friendly bacteria that help with regularity. You can buy this over the counter in any pet store.
4- If after doing the above you do not see improvement within 24 hours I would have him checked by your family veterinarian for a hands on examination. If at any point he becomes lethargic, vomiting, abdominal swelling, pale gums, etc. have him checked by ER veterinarian.
My goal is to provide you with excellent service - I hope I've provided the information you were seeking, if you feel you have received anything less, please reply back as I am happy to address follow-up questions. Kindly rate me when you are done.