The only two times my Irvine .53 ran poorly was when I lost muffler pressure to the tank. First time the pressure fitting came out of the muffler and fell "somewhere" and the second time I forgot to connect the line after I had fueled.

BTW if you ever lose your muffler pressure fitting it appears to have metric threads. If you can't find a metric tap, chase the threads in the muffler with an 8x32 tap and insert an 8-32 pressure fitting using some loctite.

My experience.

Dan