I had similar issues when running WVO, it would run good for a bit, then like crap, turn it off for half an hour and it would run good again, I opened up the access panel to look at the tank and there was a little bit of crap in there, some metal shavings and the filter sock had like a varnish on it. Blasted it clean with air from the inside out, then used a little 12 volt pump, two pieces of hose and a cheap clear inline fuel filter as a vacuum to suck the debris up, and the output of the vacuum just dumped back into the tank. Works good since.