If your choke (enrichment valve) is not working you will run rich when the engine warms. It sounds to me like you have a vacume leak at intake manifold base or a timming issue. Go back and make sure you have it in proper timming then check for vacume leak. Yes you will have to rejet when adding a uni filter but it should not cause it not to run or start, this is why I believe you have either a vacume leak or timming issue.
TOM
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