Slow Cold Cranking 420 SEL

[William]

I have a 1986, 420SEL, and when starting from cold I have to spin the engine several seconds before it will crank. When it does start, it misfires a time or two and runs rough for the first few seconds before smoothing out. When the engine is hot, it cranks quickly on the first spin and runs smoothly from the outset.

I recently completed a full valve job, renewed the timing chain and replaced all components in the ignition system. I wondered if the "cold start valve" might be causing the trouble, but it's my understanding that it doesn't come into play until the ambient temperature falls below 49 degrees F.

I welcome your remarks. William