Advanced timing will increase tailpipe hydrocarbons (unburned fuel) significantly, especially on a cold engine. Timing set around TDC will usually produce the fewest hydrocarbons, but the engine will run sluggish and possibly hot. In the earlier days of emissions testing, retarding the timing was an easy trick to clean up a car failing for high hydrocarbons. Retarding the timing could reduce the tailpipe hydrocarbons by 1/2 to 2/3rds. Manufacturers have been retarding timing on cold starts for years to clean up the tailpipe.
John
