I have a 87 CR80R that not running. I lent it out to a friend to let his kid learn to ride and he gives it back not running. Of course he said he could never get it running but it did come back with a new tire. I have cleaned the carb many times, changed spark plug, changed the coil, and changed the reeds. I can crank it and it turns over freely, it even gets the pipes hot and pops out some smoke. What should I try next, any input will help.