I have a older heil furnace (Model#867.769445) about 20 years old. When the pilot turns on after a few seconds the burners light, then after a second or two they shut off, on again, and off. They will do this continually until finally they stay on or the furnace stops trying to heat. I have also had it where the pilot turns on but it never tries to turn on the burner or release the propane. Could this be the control board.

It is probably the themal pyle (pile?) the thermal heats up and sends milivolts to the control board and tells it to light and stay lit. Do some research and see what the milivolts are supposed to be and use a volt meter to test it. It could also be dirty I suppose clean it out and make sure it is conducting heat well. I must say furnaces are not my area of expertise but I know a little about propane sysytems and robert Shaw control valves.
Good luck let me know whwt works.

Ps sometimes you can turn the pilot light up if it is not large enough.

There is a flame detector or roll out switch. If the control board doesn't get a flame detection signal shortly after the gas turns on, it kills the gas. Finding and cleaning the flame detector may fix the problem. Or the switch may need replaced. The control board could be bad too.

Thanks very much! I took the 2 screws off that hold the pilot and the switch on and cleaned them. They didn't look to dirty but I also noticed the poles were quite far apart so I bent the farthest one from the pilot a little. I restarted the furnace and immediately after the pilot turns on the burners start and stay on. Amen! Thank you for your replys they are greatly appreciated.