Stalling when parked nose-up
 

When I park my car at an upward angle and restart the engine it sputters and dies. The car runs fine when parked on a flat surface or downward angle. I've checked the filters, the tank screen, the tank vent, cleaned all the check valves and banjo bolts and lengthened the spring on the fuel pressure valve, and replaced several possibly suspect fuel hoses.
Of note also is the prefilter, which is only about 1/2 full no matter how much I hand prime it. Small bubbles appear as well. Could my lift pump be bad?
Car is a 1973 220D.

Yes it could be the Fuel Supply/Lift Pump.

Do you have the new style Hand Primer on the Fuel Supply/Lift Pump? The old style hand primer one has a hard plastic knob on it that is usually white. Also when you pump on them whe worn out they usually leak fuel and become a source of an air leak.

If your hand Primer is by your canister fuel filter (if you have that type of fuel filter) I don't know if it is possible for them to get air leaks.

The bubble in the plast filter is normal as long as you do not see bubbles moving into the Fuel Supply/Lift Pump.

It's got the newer style hand pump.

I know a bubble in the prefilter is normal, but this is large enough that the air in it can get sucked into the pump.

The pre filter bubble I consider a constant. The small bubbles transiting through the pre filter are an abnormality.

When you park the car with the front higher it is reasonable that more air gets pulled into the system. Simply because the suction force is higher.

This car is old and the rubber hose at the back near the tank is suspect. As well as some line leakage at a clamped hose joint or the line itself.

The pre filter is before the lift pump and the primer pump so they are not where the bubbles are being created by air entering the system. Sometimes it is even a cracked prefilter or a clamped hose line entering it is allowing air in.

Park the vehicle nose down.

Take the fuel return hose and pinch it closed...

Pressurized the fuel tank about to 10 psi, then look for the fuel seeping out.

Fix whatever is seeping fuel...

What size(s) is the little hose that runs from the tank to the hard metal feed line?

I've replaced just about every rubber fuel line. Nothing appears to be leaking. I don't think it's the lift pump because it runs fine until the engine is shut off.
Yet it still does it.
Any ideas?

Do you still have a stream of bubbles going through the pre filter? If so air is still getting in some where..

73220: That little piece of fuel hose is 10mm on one side and 8mm on the other, it is available from Pelican.

It probably is time to rebuild/replace the lift pump.
Most likely the o-ring/check valves in the lift pump have worn out after many years of faithful service, and you are (partly) losing prime as a result.

I believe your lift pump is MB part number 001 091 53 01, Bosch number 0 440 007 014.
Still available new, not to bad a price considering it comes with a new primer pump

You will also need a new fuel pump gasket, MB part number 0000911780.

Edit: You can test for losing prime overnight.
Park uphill and install a fuel line clamp on the rubber fuel feed line just before the lift pump.
If it starts up in the morning without issue, right after you have removed the fuel line clamp, you will have found the cause.

Hope this helps.:)

I know I saw a rebuild kit for the lift pump not long ago but now I can't seem to find it.

No complete kit for the 0 440 007 014 lift pump according to this thread:
http://www.peachparts.com/shopforum/vintage-mercedes/370355-75-240d-om616-lift-pump-part-numbers-parts.html

Here are the unblocked images of the Bosch 0 440 007 014 lift pump and the Bosch parts list for the 0 440 007 014 lift pump:

I am looking at my DGK306 rebuild kit I have and it does have the pressure spindle o ring and some other o rings that would be used for our pumps. The only problem i see with the kit is it has a mounting gasket for the MW or 3 hole lift pumps and not the M or 2 hole lift pups. Which can be ordered on it's own.

I did notice that there are numerous air release holes in the bag that holds all the components; that smaller o ring could easily fall out.

Changing the valves and O-rings in the lift pump fixed it.
Thanks for the help!

Congrats, thanks for reporting what solved your problem, not every one does.