I bought this old bike so I could have fun, and so far it's just being frustrating. I'm going to regale you all with the whole story to see if you can give me any advice.

I bought this old XT 600: it was running and riding well. I took it out on a trail and it did great except for being really hard to start when warm. The next day, I started it up and it ran fine except that it idled really high after it warmed up, so I figured I have an intake boot leak (and one of them is pretty much shot, so I think I'm still right about that). It also became increasingly difficult to start.

I took it apart and did all sorts of stuff: cleaned the carburetor (which the previous owner told me is stock except for a bigger idle jet), fixed a sticky choke lever, adjusted the valves and decompression cable. It was still a pain to start, but I did get it running. I replaced my rectifier and my ignition coil (which had absurdly high resistance) and I've now got a good spark when kicking it, but it's almost impossible to start. I couldn't get it running today.

I'm not an expert with carburetors, but I think I got everything pretty well cleaned out and running properly. I know my fuel mixture needs adjusting, but I'd still expect it to start. Later today, I think I'll spray some starting fluid in there and see if that makes any difference, but I could really use some advice, if y'all have any.

What am I missing? What do I check?

Restarting these kickers can always be a bitch , One reason I went to E-starters. They spin over so much faster and blow clear the intake of extra gas in a hurry.

Usually it is an indication of a rich idle/pilot circuit , what happens is when you shut it off, it gets that last "woof" of fuel(besides having too rich a mixture already) but then it doesn't get burnt or passed through . Being the motor is hot the extra fuel turns to vapor and it fills the intake and chamber with a way too rich condition so no oxygen to allow ignition . They don't start till that extra vapor is flushed through and enough oxygen is sucked in . This is why many modern single 4 strokes have a hot start lever or knob , it opens a circuit to fresh air and no fuel so they start better.

Some things I did on mine beside leaning the idle circuit out as much as possible(but it took more kicks to start cold) was an aluminum plate that blocks the carb from getting so hot from the head/cylinder . When you shut it down I'd slowly kick it over till I heard the decomp click and leave it there . Also if you have a way to twist the throttle wide open so as it sit there is more area for the fuel vapors to air out. Don't ever hold the throttle open when kicking though , that can be a quick way to a broken ankle , these thing backfire with force.