Depends on where you've held the poll. If you took that poll in the home town of A, and asked mostly his relatives then the poll is extremely unreliable.
What counts is demography and the number of people who will do the actual voting. This poll would be more reliable if only 10.000 people would vote than when 1 billion people would vote. You could calculate an error factor for your poll, which would be related to the ratio of people polled compared to the actual number of people who will vote. The closer you get to the real number of voters, the more reliable the poll will be.
With 110 million people, chances will still be about 50-50, not 75-25, since both candidates still have a reasonable equal chance. With 11.0000 people, it would be closer to e.g. 60-40 in favour of A, but I haven't done the exact math for this.
Btw, if you take this poll in a shopping centre, you're likely to get a different result than when you would do an online poll. You'd be polling a different audience. This is the demographic influence.
Btw, 750 + 250 equals 1000. Are the last 100 unsure or didn't they have any preference?