82 GPZ 550 engine question

Hi,
I was just testing the voltmeter on my 82 GPZ when I accidentally brushed up against the exhaust header(I had just had it running) and noticed that the pipe did not seem very hot. I decided to check all the pipes and three were quite hot and the pipe coming off the cylinder furthest to the right(when seated on the bike) was only warm. Touching it with a wet finger was quite noticeable compared to the other 3. Any ideas what is causing this and what I need to do to fix it. The bike seems to run perfectly smooth without any hesitation or stumbling. Any help you guys can provide will be greatly appreciated.
thanks,
Dan

Check for spark, then if that's good, check compression. Should have a nice thick spark at the spark plug.