Recently I have noticed the flame on my burner cutting out about every 3-5 seconds. It will loose flame for just a fraction of a second, but seems to be getting worse. Checked air & spark and they look good. I did some research tonight and I am thinking that the o-ring is bad. Apparently if there is any damage to the o-ring, suction can be lost resulting in no fuel for a short time.
For a test I connected my metering pump (that I haven't started using full time yet because of oil drip problems I need to solve) to the burner and fired it up. At low pump speeds it still did the cutting out, but when I turned the pump it went away. I am thinking that with a little pressure from the pump, the o-ring doesn't leak and provides a continuous flame.
I will try to locate an o-ring in town tomorrow and give a new one a try. Updates to follow....