I took this machine out to a local event this past weekend (along with a bunch of other machines) and encountered some troubling issues.

issue 1. The machine can be started up and everything seems fine, then suddenly (with nothing being done to the machine) the engine will rev up (almost sounds like its redlining) and nothing I do will get it to idle back down. When it revs up I have tried hitting the run/stop switch and turning off the key, yet the quad continues to race the engine until I hit the thumb throttle several times and basically "bog" the engine out. Then it will stall itself out.

Issue 2 is mentioned above. When the machine is redlining itself, neither the engine kill switch nor the key will shut it down. Both were working fine prior to the engine starting it's erratic behavior.


Any assistance on this would be most welcomed as I have never encountered anything like this before.

 

You can check the obvious such as cables, carb slide,etc,but sounds like it's sucking air and getting hot so quick it's "dieseling". That is the heat from the piston /combustion chamber is hot enough to ignite any fuel. Usually this is from an air leak or lean jetting. I'd do a compression check and also a leak down test to see if it's a leaking gasket,intake manifold or crank seals.Had this happen on water craft before even in our test tank. Wasn't a good feeling having to choke an engine down that's racing wild.

 

Sounds good, I will do that as soon as possible.