Vintage Cars: 1972 350SL, brake calipers, fuel pumps

Question
QUESTION: Hello Ron,

My cousin recently acquired a 1972 Mercedes Benz 350SL with the 4.5 liter V8. It has about 149,000 miles on it. The car sat for awhile before it was given to my cousin. He just had new brake calipers and lines installed. The fuel pump was also replaced, which I feel may be related to the problem.

When initially started, the car fires right up and idles smoothly. After a few minutes it becomes much rougher while still parked. When driving, the engine does not want to provide full power and seems like it has a miss. The engine did not want to rev up, even under full throttle. I am thinking this could be an issue with fuel or possibly spark?

This problem arose shortly after the fuel pump work had been done. Do you think the fuel system could be clogged, or those parts installed incorrectly? Any help you can provide would be greatly appreciated.

Thanks,
Jerry

ANSWER: critical that the fuelpump is the correct pump, these cars require a fuel pressure and damper that very few if any "off the shelf" fuel pumps can produce.  Where did the pump come from?
If it is the correct pump , I would next check to make  sure timing is correct, and trigger points are clean.  How long since injectors have been serviced?

---------- FOLLOW-UP ----------

QUESTION: Ron,
The pump is by Airtex, and is supposed to be applicable with the car.
When I first looked at the car I checked the new pump to see that it was installed properly. Everything looked fine, but I do remember that it was not held in place very tight by its bracket and I centered it.I just spoke with my cousin today and he said that it drove much better after I fiddled with it. He then tried moving the pump slightly and noticed that it made the engine run worse.
Would you agree that the movement of the pump could be causing this? If so, would I be able to buy a new replacement bracket to hold the pump securely?

Thanks,
Jerry

Answer
You need a pump that will deliver 1 litre in 30sec when voltage is at least 11.5V and fuel pressure is 2 - 2.1bar (29 psig)

There are many pumps that might do that, but many can put out a lot more pressure - maybe 90 psi or more. It needs a suitably rated internal relief valve. The flow should also be checked, because D-Jet pumps circulate more fuel and have a higher flow and lower pressure rating than the after market pumps.


the correct D-jet pump has an internal relief valve that limits output pressure so that rubber hose connections  won't blow off (and perhaps cause a fire) if for some reason pump malfunctions or a return line gets blocked .  Airtex or similar pump can be used as a spare but not as a daily use item , my opinion here.


If I recall they are all small in diameter and would need an adapted rubber mounting sleeve

this is the pump you need
http://www.benzworld.org/forums/3911049-post32.html

to your specific question, these pumps need secure mounting as they move a great deal of fuel, if they suck air ( not level or sitting at an angle) air can cause rough running.  So yes , however condisder above, and if you decide to keep the pump , for saftey make sure all fuel hoses are in good shape and clamped appropriately