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Backfiring Through Carb

This situation can only occur when ignition or combustion reaches the fuel intake port, causing the fuel in the intake to become ignited and blowing back out the carb. The most common reasons for this situation are: 1. Improper ignition timing or sheared flywheel key, which will require replacement of the flywheel key. 2. Improper valve lash adjustment. Requires adjustment according to manufacturer's specifications. (This can be especially true for OHV designed engines.) 3. Worn or damaged intake valve or valve seat requiring a valve job and or repair or replacement of the valve seat. Other possibilities could also include weak or damaged intake valve spring, or possibly the intake valve is sticking in the valve guide, both of which should be checked and corrected during the valve job.