Suburban NT24SP Gremlins

After 5 years of my Suburban NT24SP furnace working great it decided not to fire up this season. Having a problem with the burner lighting. Have a pretty full propane cylinder and the other gas appliances work. Plugged into shore power. Blower comes on with thermostat. It sounds like the gas valve opens and I can see a spark but no flame. I checked the electrode position and it seemed to be in spec. I thought the issue was a wasp nest in the intake but after cleaning that out of the combustion air chamber it still wasn't working. If I cover the exhaust vent I can get the burner to light but not stay lit and eventually go into lockout. It would seem based on that there is either not enough air or gas to light properly unless the exhaust is blocked and those two things can build up more. Maybe when it does light it is too weak a flame for the electrode to sense. With no more wasp nest there should be plenty of air and having shore power I wouldn't think voltage would be an issue as the motor must be producing enough airflow to operate sail switch. On the gas side all I could figure is maybe the gas orifice or burner is partially blocked. I've had the burner out which is a bit rusty but the ports dont look clogged. Not sure how to access the orifice and remove the line it is attached to. Perhaps there is some other culprit I'm missing. Any ideas or advice would be appreciated, thanks.