I'm trying so hard to figure out the fuel supply problem in my rear carb! I don't see any fuel coming out of the accelorator pump nozzle. I have already found that it is not a stuck needle & seat problem (where the float is). I changed my fuel filter. My car is stalling out if it is under load. The only thing that keeps it going when I start it is the fast idle choke when the car is warming up. I also blew on the opening where the fuel initially comes into the rear carb and forces the needle down. there is no blockage there. The jet is clear and there is fuel in the area where the float sits! I just had these carbs completely rebuilt! I also have diagnosed that it is not a problem with the dwell setting in the distributor and all of the spark plugs are good. My timing is fine as well. I'm so confused!

The accelerator pump plays no part in a constant load condition. You have a restriction in the main metering circuit most likely. Either that or too large of an air bleed.

The accelerator pump problem is probably a stuck check valve or bad plunger skirt. Float level is always critical in a carb and blowing through the fuel inlet with compressed air doesn't sound like a good idea to me.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

In addition:

Is the little fuel delivery nozzle clear? You can use a small piece of wire - like telephone wire to clean it out.

Is the arm that pushes on the piston moving? They can get corroded and stick in the "down" position.

Maybe your rebuilder left out the spring that pushes the piston back up.

If your rebuilder messed with the throttle adjustment that sync's the carbs, you may need to re-sync them to get the car to run right. LOTS of posts on the Vintage Forum on how to do that.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Turns out that there was too much carbon build up in the engine, and it just needed to be "blown out". Well, at least I did learn more about carbs!

Good evening!

I was prowling around here and found your question.

I can't see where the carbon build up stopped fuel delivery through the accel pump output tube.

In any case what may have happened is the the little lever on the side was missaligned on the "throttle lever" or just stuck in the up position not allowing the pump to prime.

Also, don't forget that there are TWO accel pump check valves, one for the gosinta and one for the gosouta. If one stuck in the most inoportune position, that would cause the same symptom.

Another thought is that if they were rebuilt, and the diaphragm was left out of the fuel for a short while, it warped and luckily it came back to life. Generally if they do dry out, ain't no fixin it , 'cept for remove & replace.

Probably it was a lever thing and taking the car out on the road and tromping on it freed it up.

Happy MB motoring!!

Mike