Gas and Oil Home Heating Furnaces - furnace ignition problem

I'm strictly a novice on this subject, so I'll get right to the problem at hand. I have an Armstrong Ultra SX80 gas furnace. The exhaust fan comes on and igniter warms up and glows red. The pilot burner lights but no ignition. Sometimes after 15 or 20 minutes the main burner lights and the sytem works as it should. Also, at times I will hear 3 or 4 clicks in a row after the pilot light starts to burn but no ignition. Now, if I blow into the vents toward the pilot light, this seems to jump start the ignition process. Whats up with this strange behavior? Thanks in advance for your help.

the main valve may be sticking. put your hand on it, do you feel it click? if so and the burners do not light, it would appear that the valve is not opening when power is applied. this can be determined if you have a volt meter and check the terminals on the valve itself. if it is recieving 24 volts, and no gas to the burners, it is bad. i believe this is a smartvalve, how old is the furnace? most had a 5 yr warranty on all parts. a company here in north atlanta who installed a zillion of these recently went under because of improper business practices, and many of their customers are now seeking help. parts are still warrantied, but customers have no labor warranty. it keeps us pretty busy!

Thanks for your advice but there are no clicking sounds now. Everything works as it should up until point of ignition. I know this sounds strange (to me at least) but I can blow across the pilot light and the main burner will light every time. Any ideas on why this happens?

orifice metering the flow of pilot gas my be dirty, not allowing flame to be large enough.