In this case, you need to say "every one" -- or just use "all" instead.
2. Redundant information:
The word "runners" refers to people who are in a race, so we don't need to repeat that information.
3. Subject-verb agreement:
If you use "every one", which is singular, the verb must be singular, too. That means you need to change "are" to "is". If you use "all" (instead of "every one"), you can keep the plural verb.
4. Pronoun reference:
Who or what does "ones" refer to? Presumably, it refers to the "race", so to avoid confusion, you should just say that.
5. Pronoun reference:
Who does "you" refer to? The context of the sentence points to the runners. We can keep the pronoun, but the runners are "they" (not "you").
6. Article use:
There is only one starting line in a race, so you should use the definite article ("the") instead of the indefinite "a".
When a coordinating conjunction such as "but" separates two independent clauses, you should insert a comma before the conjunction.
All the runners are here, but we can’t get started with the first race until they line up on the starting line.