Johnson ultra air 97 natural gas furnace , 18 years old
Starting sequence
1) exhaust blower and main blower come on
2) 2 seconds later intermittent spark igniter starts sparking , but will not ignite pilot
Will shut down after maybe 20 seconds , do not smell any gas

Things I've tried... removed pilot tubing and blew out with air
Bypassed vacuum switch
Checked all wires
Lit lighter under pilot while sparking , no gas or would have lit
Made small adjustments on pilot adjustment screw
Tapped on gas valve

Something is out of sink. The main blower is not suppose to come on and start blowing until the heat comes on and gets to a certain temp. with a meter on start up check to see if there is power going to the gas valve, sounds like valve isn`t opening up allowing the release of gas