351m lopes hard

[Crone]

I have a 78 with a 351m. At idle it runs great, but under load ( sitting in reverse or drive) it lobes pretty hard. I was thinking maybe something with timing, the carburetor (dirty) or even vacuum lines. The truck has been sitting for quite a while, I just bought it a few days ago. I was hoping someone could point me to the right direction, thank you, Bobby.

[tbear853]

Put a vacuum gauge on it and watch for a steady needle.

Rather than try and describe what you look for, maybe better to google "reading vacuum gauge", or "vacuum gauge troubleshooting " ...you will find several charts to help you make sense of the readings.