replaced an existing propane fired horizontal furnace in a crawl-space, 2 weeks-ago.I put in a heil 50k,90+ with a honeywell smart valve.Everything was o.k. until the homeowner called with a complaint about gas fumes.Went back to the job,into the crawl-space and noticed a raw gas smell only when the unit finished it's firing cycle.With the panel to the burner section off, I did notice that I could smell raw propane coming from the manifold,that is left once the gas valve shuts-off and the flames exstinguish.I took my lighter and lit this residual gas on the lower spud. This will burn for a few minutes before finally going out.I replaced the honeywell valve w/proper propane kit installed and set incoming pressure to 11"w.c. and manifold to 10"w.c. The unit fires-up and runs properly but still get that smell between cycles. Has anybody had this problem before? NOTE: all gas piping and fittings are absolutely leak free.