Small Engines (Lawn Mowers, etc.): small engine backfire, little puff, valve adjustment

Question
i have a 12hp b%26s engine just replaced the the intake valve and now when i tried to start it it backfires through the exhaust sometime very loud sometimes just a little puff what could be my problem thanks Chris

Answer
The place I would start is checking the valve adjustment. One other simple thing that can cause this is an exhaust leak. Is the exhaust valve damaged? Check these things and see if you find the answer. If not, check the flywheel key, even being partially sheared can make it out of time enough to do this.