MPS part number

[Pritchard]

I have a '74 2.0 L with stock everything. Over the past few months I have had the joy? of refurbishing the engine. I have noticed several things that make me think that a lot of work has been done on the engine prior to me. When adjusting the MPS according to Kjell's instructions, I found that the plug was not on top of/covering up the adjusting screw. In fact, the adjusting screw is backed out almost flush with the MPS housing. The engine runs rich but fairly smooth. I have tried screwing in the adjusting screw (less than half a turn) to lean out the mixture. This causes the engine to wheeze and die. I do not have access to a sniffer so I am tuning by ear at 2500 RPM.
My question is what is the part number on the MPS for a 2.0L. The number on my MPS is: 311 906 051 B. I only ask because the plug is missing and the adjusting screw is backed way out.

Thanks for any and all advice.

Pritchard