I understand your concern toward wanting to adjust the engine valve on your chipper and I hope to be of some help. While you are waiting for an expert answer, I recommend you resubmit your question and include the model number of your appliance so that the expert will provide you with a more detailed answer. I did manage to find a link that will provide you with more information about your problem: en.allexperts.com/q/Small-Engines-Lawn-1746/MDT-5hp-chipper-shredder.htm
. I hope my link is useful.