1974 280c problem
 

I have a 74 280c that idles fine if you can get it to start. When I got the car, the fuel pump leaked so I replaced it with an aftermarket electric one. The problem I'm having is that you have put a few drops of gas in the carb. before it will fire (it just turns over and over if you dont). Once running, it idles good. When you drive for maybe 30-60min (varies), the car will just shut off. It just turns and turns when you try to restart even if a few drops of fuel are added which leads me to believe it not a fuel delivery problem. I also have a clear fuel filter to see fuel going to the carb. Sometimes sitting at a light, the car would act as though it were starving for something. If you hit the gas, it would try to die out but idle again if you release the pedal. Then it might clear up and run fine for a few miles, then shut off. If it sits for a day or maybe a few hours, it might fire back up. I NEED HELP PLEASE. Any suggestion would be appreciated.

Sounds like a fuel delivery problem! How much fuel pressure are you running? Needs to be 3-6psi

IS the fuel pump mounted BELOW the pick-up point at the base of the tank?

The fuel pump is practically beside the original fuel pump in the engine compartment. It was an aftermarket Advanced Auto Parts fuel pump.

Been a while since I've fiddled with carbs... First thing that comes to mind is the accelerator pump....if you (or someone) steps on the gas (engine cold and not running), can you hear/see gas squirting in there? If it's just a dribble, try pumping like 10 times and then see if it starts. If it starts, then the culprit would seem to be the accel. pump.
I'm thinking that's a solex, and from what I remember, they like to have vacuum leaks...tightening all of the screws a little may help. Keep the fuel lines away from heat...just in case the stalling is a flirtation with vapor lock.

With some luck, some carb experts can chime in, and add more info/help.

In no particular order,

1. Check the idle solenoids. Look like AA batteries stuck in the lower part of the carb. Should click when you turn the ignition on and off.

2. Check for vacuum leaks, the AC, door locks, seatback locks, trunk lock and gas cap are all vacuum operated. As is the brake booster, which can leak.

3. Check the quality of your spark. Should be blue and may have a snapping sound.

4. If you still have a condenser on the distributor, disconnect it. You have a transistorized igniton mounted under the battery tray and don't need the condenser as you would with true point ignition.

5. For grins, try reversing the polarity of the ignition coil, especially if some one has changed it. Put it back if it doesn't help as your mileage and power will suffer if it is backwards.

6. Rotate every fuse in every fuse holder you can find.

7. I don't remember if the solex has a filter in the casting, check for it.

8. If you are drawing throught he old pump and it has a bolt in the center of a cover, pull the cover and clean the filter you just uncovered.

9. If the air cleaner cover bolt is over tightened, it can warp the carb base plate.

10. Check the valve clearance (sp?). Also check the timing chain for strech.

11. Malign Mercedes for building such a hard car to work on?

Michael

you also
 

could be sucking air. if the fuel pump is in the engine compartment. it might be that there is nothing wrong with the factory pump and it has a hole in the fuel line between it and the tank. if using a n aftermarket fuel pump it is best to put it back close to the tank. any carburated car was designed to be run on fuel that is not as volitile as modern fuel and there fore is easily vapor locked. if it is vapor lock the pump in back will solve the problem by filling up the carb bowl.

tom w

Especially if you still have the fabric covered hoses at the tank.

Michael

So am I understanding correctly that the electric fuel pump should not be in the engine compartment? That in itself could cause a problem? Also, could someone explain what exactly vapor lock is? Thanks for all responses, I really appreciate them!!!!!

Electric pumps tend to be pushers and want to be close the the source. Mechanical pumps tend to be suckers and can be farther from the tank.

Vapor lock is the unintended vaporization of fuel in the line caused by heat build up. The pumps really need liquid to work correctly.

Michael

I really appreciate the help!!!

280 C mercedes 1974
 

Is there an in-line mercedes filter under the car other than the screen in the tank and the screen in the carburetor?

Is there a fuel filter in-line somewhere other than carburetor and gas tank?