1962 Fintail 180.941 Engine - Carburetor Mystery? - PeachParts Mercedes-Benz Forum

JeffreyNMemphis · #1 12-15-2009, 01:13 PM

Hello Peaches,

I need some help getting my car running correctly. I would think it is a carburetor problem because of the symptoms, then I read something that makes me think there may be another cause.

The symptom was that the car would not sustain throttle at or above 3000 rpm with the choke off. The car sounded like it was running out of fuel. I could pump the accelerator pedal and get the engine to 4500 rpm (all tests after allowing the engine to warm up).

The carburetors were taken off, cleaned, new gaskets installed and put back on. Ran slightly better, but symptom still present. I replaced the membrane in the fuel return valve. With the choke fully on, the car runs and accelerates normally.

I added an electric fuel pump with a fuel pressure regulator to maintain 3 psi. Still getting the same symptom... Runs perfect with the choke on.

The rubber boots on the fuel dampers need to be replaced. Could that have anything to do with this? Could it be a timing issue with vacuum not correct at stage two?

Thanks in advance for your experience, wisdom and advice!

Jeffrey

JeffreyNMemphis · #2 12-15-2009, 01:24 PM

By the way... In gratitude I always wish to give something back since the folks here have given me SO much more than I could possibly return.

Someone looking for help in the future might read this thread so I offer this expensive lesson. The fuel return valve is made of SOFT brass and will break if you don't put the correct washers on and/or over tighten it.

I mauled my fuel return valve and found out from experience to use the correct washer and don't overtighten. Mercedes sells the piece I destroyed for $259.00. That is only for the valve housing, membrane and spring is extra... OUCH!!

Necrosavant · #3 12-15-2009, 02:46 PM

damper has nothing to do with it my dampers are tore up and im driving fine on highways..deffintely sounds like your starving for fuel..did you shoot air through all the passages while valves where out..was the car having this problem before? before i rebuilt my carbs i had to pull the choke out just to idle and push it back in to drive...also out of curiosity what gasket kit did you get for your cabs (royze kit didnt have the correct accelerator pump flange gasket for my car and i had to make one)

JeffreyNMemphis · #4 12-15-2009, 03:10 PM

Yes, shot compressed air though all the passages. Still found silt in the bowls a week later despite changing fuel filters twice and having the gas tank cleaned to bare metal. I cleaned the carb bowls again. And, I will probably take them apart again soon to clean one more time.

I had the gaskets in my collection. Each one was fresh and identical fit for what came off, including the flange gasket. I have three extra carburetors and plenty of carb gaskets, valves, etc. I may rebuild another set and try swapping them out. The spare set has good damper boots. I was just hoping to avoid rebuilding carbs again...

It sounds like it is starving. But I shut it down but covering the throats, turning off the key, and then taking the tops off. Float bowls were full of fuel. Something is not flowing correctly is the likeliest scenario. Was thinking perhaps the timing is not letting it burn?

Necrosavant · #5 12-15-2009, 03:28 PM

What is your timing set at right now? i had mine set at 2 degrees and retarded it with the fine adjustment about 2 notches to stop the clatter

JeffreyNMemphis · #6 12-15-2009, 03:32 PM

I will have to check the timing... I don't have any clatter. The engine sounds ferociously strong when revved up.

Necrosavant · #7 12-15-2009, 03:44 PM

oh yea, was amazed how it roars when racing up the roads for such a small 6 cylinder...yet sounds like a sewing machine at idle

..also would be curious to what fuel mileage people are getting in this car i read somewhere it should be 21 mpg and im getting about 16mpg right now
---i didnt have any clatter when i got the car but after tune up and i reset the timing to spec. i had it... then i found out that this engine is supposed to run on 97 octane and if you run a smaller octane rating what they called (inferior fuel) 93 octane in my case it will cause enging knocking (clatter) so i retard the timing slightly and ive been putting about 2 gallons of 100 octane every fill up and it sounds nice now

t walgamuth · #8 12-15-2009, 04:01 PM

Float adjustment can cause starvation. If level in bowl is too low it will run lean.

JeffreyNMemphis · #9 12-15-2009, 04:04 PM

Quote:

Originally Posted by t walgamuth

Float adjustment can cause starvation. If level in bowl is too low it will run lean.

How do you adjust the float on this carburetor? Thanks in advance!

Necrosavant · #10 12-15-2009, 04:44 PM

you adjust float level with diffrent size washers under float valve...but manual states to always use the smallest washer and worked out for me

JeffreyNMemphis · #11 12-15-2009, 04:59 PM

Thank you very much! I have a few possible things to check now. I will report back when I figure out what fixes it.

Pooka · #12 12-15-2009, 07:19 PM

The 'clatter' you describe from running the lower octane gasoline is correctly called 'pinging'.

Why I don't know. It sure sounds like clattering to me!

I only mention this in case you run into a part in the service manual that addresses pinging and what to do about it.

250 Coupe · #13 12-15-2009, 10:04 PM

Just for fun, you might want to put a vacuum gauge on it.

See,
http://autospeed.com/cms/A_2393/article.html
and
http://www.gregsengine.com/vacuum.htm

Or search for "diagnose engine vacuum gauge" if the links get blocked.

Also, be sure your ignition is up to snuff. A weak spark, incorrect dwell, a bad condensor and wrong polarity can cause problems at higher RPMs.

Michael

t walgamuth · #14 12-15-2009, 10:50 PM

Most floats can also be bent at the tab that pushes on the shut off valve. be careful though a little will do a lot.

cth350 · #15 12-15-2009, 11:27 PM

There are two methods of computing octane. In the US, the standard is to average them. The old mercedes manuals are referring to "RON", or "research octane". That's higher of the two numbers being averaged.

I recall seeing tables of RON vs MON, but I'd be at a loss to say where they might be now. But using current mid-grade gas should be more than good enough.

As for the ignition, it's a very good exercise to put it "to spec". Get the dwell right and get the timing right. And that means setting it at 4500 rpm and testing it at 800, 1500 and 3000 rpm. Also check the impedance of your plugs, wires and cap.

After all that, fix your float height.

Thx -CTH