[Paulporsche]

Sounds to me like your mixture, especially when cold, was a little lean to begin with. When you added the SSIs your mixture then needed further richening.

If you search, you will see that a too lean mix can be due to several things, including an out of spec WUR giving you a control pressure that is too high, vacuum leaks, or sometimes just a too lean setting. If you have a 5" long 3mm allen wrench you can richen the mix via the screw down in the top of the fuel distributor. A clockwise 1/8 turn may be all you need. You can also verify your control pressures w/ a pressure gauge to make sure your mixture is correct under all conditions.

As mca and others have said, however, if you are unsure about this, or don't have the tools , have a shop check your control pressures and set your mixture.