Where is the fuel filter? - PeachParts Mercedes-Benz Forum

#1 03-07-2004, 07:10 AM

I'm going to replace the fuel filter on my '72 250 (twin Zenith's), because I think it could have something to do with the hesitation and occasional stalling of the engine. So here is the question: WHERE exactly is it located? The Haynes manual doesn't even mention a fuel filter for carb engines. If someone could tell me where to find it, I would appreciate it.

An another thing: I noticed that something is leaking from the floor, on the left side just behind the driver's door. It looks like engine oil but it smells sort of like tar, so I'm guessing it could be from the undercoat, or some sort of rustproofing from the cavities.

/Olof Winterfjord

Mark DiSilvestro · #2 03-07-2004, 09:26 AM

My factory Mercedes W114/W115 repair manual shows a plastic screen, attached to the inside of the gas tank drain plug. Mechanical fuel pumps will sometimes have a screen under a removeable cover. Some carburetors have screens in the inlet where the fuel line connects but I'm not sure about the Zeniths and I've misplaced my Haynes manual. Check the exploded-veiw Zenith carburetor illustrations in your Haynes.
I don't think these cars came with a proper, easily replaced fuel filter.
In the engine compartment of my '72 250, I've installed an in-line filter in the fuel hose, just before the fuel pump.

Happy Motoring, Mark

#3 03-07-2004, 10:36 AM

That in-line filter sounds like a good idea, once I remove the filter that I expect to be clogged.

FastLane lists a fuel filter for this car, the standard type with a paper filter inside a plastic cylinder, with inlet and outlet in each end. Now if that is what I'm looking for, this shouldn't be too hard. But it seems things are not that simple...

Mark DiSilvestro · #4 03-07-2004, 03:55 PM

That filter from Fastlane is the inline filter I was talking about. You might not already have one on your car. If not, you will need to split a fuel hose someplace convenient and install one. Mine is in the hose leading to the fuel pump.

Happy Motoring, Mark

300SDog · #5 03-07-2004, 05:09 PM

Each Zenith has its own internal fuel filter too..... a small brass cylindrical screen that gets cleaned instead of replaced. Accelerator pumps can also be issue on Zenths..... these are the small piston devices with rubber boots and arms.

Regarding inline fuel filter, can recommend the 240D clear plastic "L" shaped primary filter..... its size will fit standard fuel line, say running from fuel pump to carbs. Cost on the 240D primary filter is about $3 USD. Short side of "L" faces forward. Filter element is fine plastic screen and clear plastic body lets you see what gets filtered out out of the fuel.

#6 03-07-2004, 06:07 PM

Oh, so THOSE are the fuel filters in question! I don't have the repair manual at hand now, so how do they come out, and how do you clean them? And for the accelerator pumps: What can you do with them to increase performance? I'd rather not deal with carburator adjustments unless it's necessary

My problem is that the car accelerates poorly when I increase the throttle. Feels like the engine is filled with chewing gum. If I get those brass filters cleaned I might also get that extra filter on the hose, to prevent them from clogging up.

Thanks for all the help!

Olof Winterfjord

ctaylor738 · #7 03-07-2004, 07:03 PM

There is also a fuel filter in the fuel pump.

There are two types of pumps. The older with the diaphragm that is held on with screws has a brass filter behind the hose fitting on the inlet side.

The newer type has a cone-shaped filter on one side of the diaphragm. The cover is held on by a small screw.

I have always thought that installing an inline filter in front of the fuel pump made a lot of sense.

#8 03-08-2004, 10:31 AM

I tried to open the fuel pump, but it was too hard with the tools I had at hand. It's the newer type of pump, but the tiny screw was to hard to reach. I will try again though.

Before I do something stupid, am I at least a little bit right when I say this will make something better? It's really bugging me that an 6-cyl engine has the acceleration of a lawn mower.

ctaylor738 · #9 03-08-2004, 10:53 AM

Before I messed with that screw, I would clean the two in the carbs and check the fuel pump's output by pumping into a container with the starter turning. I am not aware of any specs but you should get a good amount of fuel - definitely not a dribble or a weak squirt.

If you are getting a good flow, I would check and see if the secondaries, which are vacuum operated, are free to open. I recall that the car sat for a while and they may be stuck.

#10 03-08-2004, 04:32 PM

I can't find the fuel filters in the carburators. I didn't see them in my Haynes manual, or in this Zenith manual:
Zenith Carb Manual
Any idea on sort of where to look...? Carburators are not really a place to turn every screw until you find the right one. I know I'm being a pain here, but I'd hate to screw this up.

The Zenith manual also indicates that the accelerator pumps are worth checking out, as mentioned in this thread.

I appreciate all the help I can get (as if that wasn't obvious beyond belief)

ctaylor738 · #11 03-08-2004, 04:51 PM

If you have them (not all carbs do), they are in the body behind the fuel line fittings. Loosen and remove the fuel lines and then unscrew the brass fittings from the carb bodies, and you should be able to pull them out.

You can find a picture on Fastlane.