I have a 1980 XR500. I’ve been slowly restoring it over the last 3 years. The first engine rebuild was botched. Guy had no clue, got specs wrong, etc. Second rebuild was good, I guess. Professionally done by a very knowledgeable (older) person at my local bike shop. Carb is rebuilt as well and jetted correctly. It’s tip top. Air filter is clean. Spark is fine. New coils. Tons of compression. In theory, the dang machine is practically brand new. Ive only been able to get it to crank a few times since everything was done. Now...can’t get it to do anything. Tried again this morning for 30 minutes...thought I would have a heart attack. Still. Won’t. Start!!!!! Yes, I am performing the correct starting procedure. I’m at my whit’s end here. What am I missing?!