Backfires ... when I press down on the accelerator, it starts for maybe 10-15 secs but I have to keep pumping the accelerator in order for it to keep running(it backfires when Im doing this also), after the engine gets warm or hot enough it will idle, and not die.

This could be either a vacuum leak or a choke problem. A vacuum leak will lean the mixture and make the car run worse warming up, when it needs a richer mixture.

But it could also be the choke. When you start it, you pump it a couple of times to close the choke plate. If it doesn't close, you have a problem.

You start the engine, and vacuum actuates the diaphragm in the pull-down. Look on the back of the carb, and you will see the vacuum line from the base of the carb to the diaphragm.

With the engine cold, remove the vacuum line from the base of the carb, and connect a Mityvac. Pump it to supply some vacuum and observe the choke gap. It should be around 1/16th of an inch. This is the gap between the front edge of the choke plate and the carb body. There is a set screw on the diaphragm that it used to adjust the gap with vacuum applied. If it's larger than 1/16th, make it smaller. Continue to reduce it and re-test until you get a smooth warm-up.

__________________
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

hmm, you must be the same ctaylor I emailed a about the engine pictures, lol. Choke was checked, it's fine. There is no vacuum leak. I got it up to 1omph before it did a serious backfire,...kinda weird though is that I press on the accelerator I hear the engine reving up then it backfires and slowly accels to 5mph, but can't give it too much gas .. you know what happens, So hope that better helps narrow it down.

This is a tough problem to fix, because everything has to be just right for this engine to warm-up and run right.

So, in no particular order and without regard to what you have already done or checked.

Something is depriving the engine of the enriched fuel/air mixture that it needs to run well when cold. The possibilities are limited, some have already been discussed. Here, in no particular order, you can work the list from easy to PITA.

- Air leaks at the carb's top plate. Not much you can do besides look for distortion, double up good Mercedes gaskets. Try known good carb.

- Vacuum leaks around carb or intake, broken plastic line or rubber connector or brake booster. Check all lines carefully, spray penetrating oil around carb base and head-intake manifold joint. Check to see that brake booster holds vacuum.

- Choke gap too large. I REALLY suggest that you make the gap smaller using the MityVac the way I described earlier. A tiny adjustment can make a big difference.

- Dirty float chamber. The main jets are in the bottom and can easily clog with only a little sediment. Remove top plate, observe bottom of chamber, clean and blow out as needed.

- Plugged emulsion tubes. Disassemble carb and blow out all tubes and passages

- Insufficient fuel supply. Remove fuel line, direct into container, crank engine, look for healthy spurt

- Accelerator pump not working. Open throttle quickly, look for healthy spurt from pump nozzles

- Fuel return valve malfunction. Disconnec and plug vacuum connection or bypass valve with hose.

Some other causes IMO less likely:

- Insufficient timing advance. Check vacuum and mechanical advance

- Tight intake valve. Check valve clearance.

- Damaged intake valve. Run compression check

Good luck,

__________________
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

If your choke plate seems to act normally. Try using a can of wd40 at any possible leakage point. You will instntly know if a leak has been found as engine will speed up or smooth ouit. There is no way to see a small vacuum leak otherwise. If by chance you do clear the fuel system then start to check the ignition system carefully.

where do I spray the wd-40?

I've heard that before...

I have the same 1973 280 with a solex 41A. I rebuilt the carb myself after it wouldn't start without starting fluid and drove it on my wedding day. Your carb is filling with gas and is popping because...it is a vaccum problem. Check your gaskets on the carb, especially the one on the left side facing the car. They crack easily and your not getting enough suction, pumping gas in there will cause that backfire...make sure too that the piston holding the float is free of grime, it can hold the float and keep you from what its suppose to do.

JOHN

sigh after all the reading and testing and rebuilding, I started to think else where..and found... well for 1 the filler on my gas tank is rusting, the gas tank has internal rust spots starting to form. 2nd my gas filter is full of rust, so maybe this is dark black stuff in my carb.. sigh, is there anyway to fix rust or some gas tank kit I can buy?

I would like to take the time and say, thank you all who have helped me thus far.