Venture 00, difficult to start on random occassion?

I have a Venture 2000 van, Some times it is difficult to start. I have notice that "the time of the day or temperatures"does not make any
difference. The poor starts are totally random. Sometimes it starts but dies unless I pump the gas a couple of times. 30% of the time it starts on first try, 60 % of the time it takes 2 to 4 tries until it will start. 10% of the time it takes as many as 10 tries. Also, I found it helps if it does not start on the first try, to take the key out of the ignition and put it in again to start. Any ideas what the problem could be? thanks
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