After I haven't used my Civic for a couple of weeks and do a short
journey of about 15 minutes, switch off and then attempt to start
about 10 minutes later it won't start until I take the fuel filler cap
off to relieve the fuel pressure - then it starts no problem. The
fuel filler cap is a not the original - I don't know if this is a
problem, should it be vented in some way?

I do 200 mile motorway journeys in the car every few months and it
always starts fine in the next few days after that...Apprieciate any
ideas! thanks.