Changed the fuel filter on the HZJ73. I noticed some whitish smoke from the exhaust and happened to pump the filter and noticed that despite the stopcock being closed on the bottom, fuel was coming out of the water drain at the bottom of the filter. I am guessing that this was allowing some air to get into the system. I got a new stopcock and more importantly the o-ring which was flattened and obviously not sealing. I wouldn't have replaced the filter which was pretty new, however, my strap filter wrench deformed the old one quite a bit (I am still waiting on the special part wrench). The o-ring and stopcock are available from US toyota dealers. Also dumped a bottle of the liquid moly in the new filter. Truck seems to be running great now.
Yep. That was a problem of mine (minus the white smoke). I had to replace that pitcock water drain and the o-ring with OEM stuff. I remember measuring the body and the groove for the o-ring with a good micrometer and it was ever so slightly small. (less than 0.5mm). The old part looked original and yellow, I guess it might have shrunk a bit from the years of exposure to fuel and heat, which is why it didn't seal for me even with a new o-ring at first.