Without using starting fluid it is very hard to start. This is on my 50 3100 216 chevy. I have noticed a vacuum when removing the gas cap. I tried removing the cap and it still only started w starting fluid.

I have heard that mud dauvers may build a nest and clog the vent for the gas tank. Is it possible to see this vent without removing the bench seat? Where is it located?

What else should I check in regards to the starting problem?

Thanks. Your responses are always helpful.