After recently rebuilding my 84 XT600 it ran okay, just some popping on deceleration. The rubber intake boots that go from the airbox to the carb weren't mounted properly though and when i put them on properly the bike wouldn't start. I thought the air/fuel ratio was changed so started adjusting the pilot screw and idle screw but still no joy. The only thing that worked was starting the bike with the boots not fully on then trying to inch them on but the bike would just die with them on. I noticed the carb making very slight in-out movement in sync with the engine which got greater the more the boots were on leading me to believe I had messed up the timing and the intake valves were open on the exhaust stroke. The exhaust also got smokier the more the boots were on and the carb was also getting warm. I figured with the boots off it gave it enough room to suck in air while also letting the exhaust out but with them on there was nowhere for the exhaust to go.
Took the head off today, removed cam chain tensioner and front cam guide, checked the timing and it's spot on!

All I can think is the intake valves aren't seating properly but I did grind them when rebuilding and although I hadn't done it before I think they were done okay.

I've spent a long time at it now trying to get it going and I'm totally stumped! Any suggestions?

P.S. Engine was getting really warm/hot - after a 30 km drive averaging 80kmph the cylinder was over 100° C - oil is flowing good tho.

P.P.S. Also, bike's used (burnt?) too much oil since rebuild