odes anyoone on ere know if these machines have a spark arrestor in the muffler? my mule will start and rev when first started but after will only idle. i have replaced the fuel filter & the air filter, didn;t help. took fuel tank off and cleaned out still didn't help. i am thinking the exhaust is creating back pressure. i took the drain style plug out of the bottom of the muffler and some black soot came out but still same thing. i know chain saws used to have spark arrestors in the mufflers and if the plugged they would act like this. anyone have any thoughts on this and if so , how to knock out or clean said spark arrestor?