All the elements for a backfire are in place, all it takes is a nanoseconds worth of fuel vapour, its always in there, the ignition element (a heat source) is always in there,, the fuel cut may be leaning things off, it certainly kills off any inter cooling of the exhaust valves by overlap events, so up goes the temp, nanoseconds again is all it takes, then all you need is some air in the exhaust,,,,,, port flanges, c clamps, when you think they can rip blades backwards on a turbine wheel
.... i think im going to look at introducing very deep valve pockets on my new wasser, so its a 'safe' engine, if there is such a thing, the energy is huge and has to go somewhere, i recon there's enough to open valves to coil bind if the springs are not up to par, i run oil jets these days to cool the springs, imagine how hot they get just from movement/friction, say on a 'cold' test rig, also remote oiling for the springs with external hard lines and a spray bar on T1 is worth looking at, the T4 Walter runs has better top end oiling, I've yet to play with these
, my equip has a very good T4 guru on hand, retired now, but a very big name from super vee in the '70s, and on to the very top of motor sports engineering, he has just sorted my wasser oil and piston ring problems with a quick look and a phone call
. thanks ...... ........