Experienced high hydrocarbons on my '88 F150 (155K mi.) and failed emissions. Changed plugs (old ones looked like they were burning clean), dist cap, rotor, PCV, air filter, oil and oil filter. HC's dropped but not enough, and failed again. On third try, I shot some synthetic 'gum-out' carbon deposit removal stuff made by Valvoline down the throttle body throats and the HC's dropped to max allowed so it finally passed.

Question is: I'd like to get HC's even lower, so what other steps can/should I take?

Thanks for your help.

 

You need to bring your combustion performance up. First of all I would do a compression check, check out your engine vacuum and ignition timing. Any of these can bring your HC count up because of incomplete combustion in one or more cylinders.