A 1976 Volvo 264 with a B21F ???

The Six-cylinder PRV B27 (Peugeot Renault Volvo ) engine was the only option for a 1976 260 series.

Retrofit?

Have you tried re-seating the spark plug cables? It sounds like it could be something simple... or at least, always start with the simple and work toward the difficult. That would be a simple thing to address electrical causes. To do something simple to address combustion, I'd throw 1/3 can Seafoam ...

I believe this engine will have a cold start injector and cold start relay to provide extra fuel when it is cold. The cold start relay may be bad or the temperature sensor for the cold start system may be bad. Do you have a service manual for this B21F K-jet? Also, if this car sat idle for many mont...

Found something. On the Red blocks the temperature switch initiates the cold start process. If the temperature switch is defective the cold engine would be trying to start on the warm start process. Other components involved in the cold start process are ECU, Frequency valve and Thermal time switch ...