Dieselling

["Tyson Sherman" <tsherman@tecinfo.com>]

Hi folks.  My 76 MGB decided to start dieselling (sp?)
again today.  It hasn't done so since April, but in the
past month it has done so 2.5 times.  
The anti-run on valve clicks like it's supposed to.  So,
what usually causes this?  It's partially de-smogged
but all of the vacuum and related hoses to the charcoal
canister are properly clamped.  So, what usually causes
this annoying thing?  
Thanks,
Tyson