M 130 engine I think too lean

[jim 56]

My car will not run for more than a few hundred yards.When it’s running it is back firing at the throttle when it gets to around 1200 rpm.I did the smoke test all looks good. I puts shims under the BC still does it. These are what three plugs look like the other three are about the same.Would really like any help I can get as i have to get this car on the road as my daily driver.

[Cees Klumper]

Could be many things? Did the car run well at any point?
Some thoughts:
- linkage tour
- leaking CSV
- ignition timing, or other ignition faults, such as bad points, wires, coil, cap, wiring. Distributor installed wrong? Firing order ok?
- valve clearances?
- fuel supply ok?
Good luck sorting this out, I'm sure others with more experience will chime in shortly

[jim 56]

Thanks for answering I believe I have done everything.CSV good, Crane ignition, Linkage tour.Rebuilt fuel pump 13PSI 1 liter in 15 seconds at return by tank filters clean.It idles nice but when I get it on road it dies in a few blocks.I am really worried about plugs they seem to tell me it is really lean.Maybe I should change to a cooler plug.This is a 1972 engine all emissions relays seem to be working well.I have it timed at 0 degrees right now I believe I read here (possibly from Benz Dr) that is where it should be.I really need help here I don't want to ruin engine if it is really lean.Thanks in advance

[Benz Dr.]

A lot to answer here. That depends on if it's an early or late USA 280. If it's a late USA 280, the timing should be right around 2 -3 degrees ATDC at idle. The advance should end around 38 degrees if everything is still working right.
Your spark plugs look really fresh as in " a few miles of driving " fresh. I'd say they're close to right but the one plug that's dark shows that it's been misfiring. I would get the injectors tested seeing as the spark plugs are all different colors.

[jim 56]

Thank you for answering.I will bring timing to 2-3 ATC.I did backflush the injectors but will get them tested.But you don't think it is running too lean?BTW my distributor ends in 068 I have not seen anywhere on site this number mentioned.Is the 38 degrees BTC still apply for this dist?I ask this because I seem to be able to get only 30 degrees at 3000RPM.




 

[JPMOSE]

Make sure your fuel return line (back to the fuel tank)  is not blocked!  This will create a lean condition, along with pressure build up that will stall the engine after running a few minutes.

[ja17]

What is the history of the problem? Also if the barometric compensator fails, the injection will go lean.

[jim 56]

Thank all for replies.Let me post what I have done (its long ).I appreicate any input of my latest readings.I am assuming I have a earlier engine serial number is 130 98012 066875.I say this because I set timing at 3 ATC as per Benz Dr. and car ran terrible.I now have it set at 8BTDC and car is running decent except for some slight backfire when accelerating.I switched to NGK BP 6ES (instead of the 5ES).They are gapped at 30.vacuumn gauge in line to distributor.
@ idle 850 RPM 16 in vac 8 BTDC
@1500 RPM 20 in vac 15 BTDC
@3000RPM 20 vac 35 BTDC
@3200RPM vac shut off timing jumped to 50 BTDC aux fan also turned on.Temperature read 180 degrees

I did split linkage again @ idle.When I open throttle slightly the idle increase slightly.(about 50 RPM).When I open FIP slightly off stop car wants to die.
I don't know if these are crazy readings I have no a/f meter I thought that the vac would drop off after throttle plate opened.
I hope someone has an opinion like I said the car is running alot better.I was able to ride around for a few miles with a little backfire.One thing aAI did want to say is I have around 2.75 mm shims under the BC.Joe according to a picture on the site the BC pin seems to be in the right place so I think its working.

[Benz Dr.]

You haven't said what year or engine you have so I went with a guess. If it runs right at 8 degrees leave it there.

[jim 56]

I,m sorry it is a 1972 280SE sedan.Do you think that the readings I posted are ok I thought that the vac should drop off with the throttle opened.Also concerened about the split linkage test.I thought that when the FIP is moved slightly off stop that engine should also increase slightly.

[FresnoBob]

A full CO meter to test air / fuel ratio is quite expensive, but perhaps you can borrow or rent one from a service shop?  I bought an Innovate Motorsports LM-2: Digital Air/Fuel Ratio Meter Basic Kit and it works well, but be gentle with it.  The meter is US$350 and I damaged the O2 sensor by accidentally dropping it.