DPM goes full rich when it fails
I know that's what it's "supposed" to do, a couple guys on here have said that was not the case for them though.
Nothing else makes sense Maxwell, he was up to 2 main jet sizes larger on the mag side for two days and the plugs were perfect. No jetting changes and it was later in the day (re: air temp was hotter) when it went lean, not a cold morning at -20. If anything it should have been pig rich on the mag side.
Why does it run like a raped ape for 2.5 days and then all of a sudden starts acting up for no reason, out of the blue? Unfortunately I wasn't there to try and ride it and he hasn't put an EGT on it to confirm plug readings and what the temps are in the different throttle positions, and my only other suspicion is that its maybe a mid range lean spot and that he just happened to keep it there for too long.
I have been through the motor myself, it's in good shape. Carbs are set correctly, other than a pipe and can, it's bone stock. Nothing left to suspect other than the DPM because if it was anything else (like carbs) it should do it all the time or right from the start, not run great for 2 days then act up for no reason. something seems to change, which is why I suspect the DPM because nothing else can physically change without him touching it - which he hasn't.