MPS mystery, huh Options

[r3dplanet]

Last winter I had some fun rebuilding my MPS unit, which is for a '73 1.7 liter engine. The MPS part number ends with 049.

According to the calibration tests on the pbanders website in conjunction with my trusty Meterman LCR55 and MityVac, the unit is perfectly calibrated. It holds vacuum without issue. The readings at 15, 4, and 0 in.Hg all match perfectly. And I mean perfectly. No variation from what the LCR55 shows to the pbanders table.

The mystery is that when I hook it up to the car the engine won't start. It tries to start and I can sort of force to keep going by blipping the gas, but it won't idle on its own. However, when I install another verified trashed out unit, the car starts right up and idles and climbs smoothly.

Um. Huh. I'm hoping that there's some other adjustment elsewhere in the system that my tired brain won't remember. Somehow maybe my car is adjusted to work around the (leaky) old MPS? Or maybe I didn't rebuild the MPS correctly. But it was in and out of the thing for days and I'm convinced the physical operation is correct. But I'm always willing to be wrong.

Confused.

-m.

[cary]

I did mine in Forest Grove.

Same meter and same results.
The car did not really run good until I set the AFR down to 12.75.

After the LCR adjustment. It was running an AFR of almost 18.
Once you bring it down under 15 the engine comes to life.

I'm almost a year after these setting. Runs and starts almost like a new car.
There's are those few minutes between were the warmup is over and it gets completely up to temp that it studders a bit.