"starts strong" may be open to interpretation, but if you have an audible ignition and the flame is a reasonable color, you may either have a poorly-adjusted or failed flame sensor (so it shuts down thinking the gas didn't light.) As mentioned above, the board and gas pressure are also potential culprits. Usually when the exhaust has spiders or other blockage you get lots of soot and it never sounds "right" if it lights at all, but making sure the tube is clear is good maintenance anyway.
Zero Gravitas — 2017 Flying Cloud 26U | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill