Kitchen sink disposal side not draining well

[dave180]

I've been in this 56 year old house for 7 years. I replaced the kitchen sink and transferred the disposal over. I now have issues with the disposal side of the double sink draining slow and filling with water. If I turn on the disposal it blasts the water out and into the drain. All is well until next time.

Now, I'm looking at the drain configuration and don't know what is happening here. It appears that the disposal side drains into the outside wall cavity underneath the drain for the right bowl. Even more confusing is the fact that there is a window directly above the sink. Looking into the attic from a scuttle hatch about 15' feet away I do not see a vent pipe and there are no 4" cast iron pipes nearby. I can DIY just about anything and I'm looking for suggestions or ideas regarding the slow drain, including capping the disposal side and running another one to the basement.

TIA, Dave

 

[TomFOhio]

Can't tell by your picture but is this a double sink? Is that copper drain pipe from the other side of the sink?
Try taking the trap and the black elbow fitting off of the disposal and see if its plugged up there. If not then a
snake will have to be ran through the disposal drain line.

 

[dave180]

Can't tell by your picture but is this a double sink? Is that copper drain pipe from the other side of the sink?
Try taking the trap and the black elbow fitting off of the disposal and see if its plugged up there. If not then a
snake will have to be ran through the disposal drain line.

I should have been more clear, it is a double sink with drains stacked on top of each other. I will try your suggestion though. Thank you