Engine sputtering/stalling when in reverse?

1965 PLYMOUTH VALIANT
80,000 MILES • 6 CYL • AUTOMATIC
Avatar
WWBANKS3
  • MEMBER
  • 8 POSTS
I have the vehicle listed above with a Slant 6 motor. Whenever I shift into reverse, the motor begins to sputter intermittently and eventually stalls out. However, if I press the gas while in reverse, I do not have this issue, but this is obviously not always possible when backing into a parking space, adjusting parking, etc. Is there anything I can adjust on the carburetor and/or motor to prevent this from happening?

I have attached a brief video for reference along with photos of the engine and carburetor.
Images & Video (Click to enlarge)
Attached Media
Attached Media
Attached Media
Sep 19, 2025 at 9:57 AM
Advertisement
Avatar
STRAILER
  • CERTIFIED EXPERT
  • 53,854 POSTS
Most of the time this will be a vacuum leak, I would start with the choke pull off, I have seen these leak. If you remove the vacuum line you should be able to push the plunger in and put your finger over the vacuum port and it should hold. Also, this video will help as well

https://www.youtube.com/watch?v=LRKWV4Are5c

You can get the machine for about $65.00 on amazon, I would check the base gasket of the carb and the PCV valve line and valve, these are other common places for a vacuum leak.
Sep 19, 2025 at 10:39 AM