Rough during warm-up enrichment period

[Wallace White <wallace@remdesign.com>]

When truly cold (i.e. not run for more than 12 hours or so), the 5kcstq
is having problems. It starts without any problem, runs fine for about a
minute, and then starts stumbling--at idle, at rpm, whatever. I believe
it is not getting spark or it's getting too much gas, given the smell of
gas and the painful sound of a backfire or two. Sometimes the missing is
really bad, and if the engine dies, it is very difficult to get it to
start again. Once it finally starts again, all that unburned gas
backfires.

Once the engine is warm, or if it is started again even many hours later
(after getting warm enough the first time), it runs fine.

My first stab at this problem was unplugging the cold start valve,
though I didn't expect this to be the problem. Sure enough, that didn't
make much difference. I started looking through the Bentley for help on
the warm-up enrichment, which sounds like the problem, but I wasn't sure
what to try. 

Any advice would be appreciated. Thanks!

- Wallace
  '87 5kcstq 149k