I do some work that requires a chain saw. Somebody gave me a McCullough Mighty-Mac (I think that is the model, at least XXX-Mac), 16" bar, several years ago. I knew it wasn't much of a saw, but I have used it many times, and has served me pretty well for my limited needs. Yesterday, I cut down some badly overgrown yew bushes and hauled away the debris (bonus work for this time of the year!). In the morning, it ran pretty well, started with a little difficulty. But, in the afternoon, it would start OK when cold, but I had great difficulty getting it started when warm (e.g. after refueling, or after loading debris for hauling). I used it for a job last Fall, and had similar problems. Taking out the spark plug, cleaning with wire brush, and reinstalling, usually helps enough to get it started, albeit difficult. I installed a new plug last Fall near the end of the project, saw improvement, and I felt the problem had been solved. Now, I believe the problem is beyond the plug. I have not tinkered mechanically with chain saws. I have inspected and cleaned the air filter. I have insured the choke works properly. Also, I checked exhaust ports and found them clear. The one thing I'm questioning is the primer bulb functioning properly. However, I know that it must be working when the engine is cold. For other engines, use of the primer for warm start is not necessary. But, I have tried it on this chain saw as a secondary tactic, not as a matter of course. The other item causing the problem might be a coil. Like I said earlier, I've not tinkered much with this machine, so I don't know "what's under the hood." I don't even know where to find the coil on this engine. Any suggestions on a good place to start troubleshooting? Don't suggest buying a new chain saw. I'm too close to being tempted, but my use is so limited I have a hard time spending $300 or so for a good Stihl saw.