THE HEATER STARTS THEB BLOWS ALOT OF SMOKE

Question

I HAVE A REDDY HEATER 55000 BTU. IT ALWAYS RAN FINE BUT NOW IT WILL START UP THEN IT SHUTS OFF AND BLOWS ALOT OF SMOKE. IT WILL KICK BACK ON AND SHUT OFF AGAIN BUT ITS TOO MUCH SMOKE. SO IM GETTING FUEL AND I HAD THE TOP OFF AND IT GETS GOOD SPARK. I TOOK OFF THE THE AIR FILTER AND THERES NEW FUEL IN IT. WHY WONT IT STAY RUNNING ANYMORE ??? THANKS !