No start - PeachParts Mercedes-Benz Forum

my76-280s · #1 07-17-2007, 04:56 PM

I own a 1976 280 s. M110 engine w116 chassis. The car started right up and I left it idling for 30 minutes while I rearranged the garage shelving. Turned the car off and it sat for an hour. Started the car to go for a drive and it stalled 2 blocks from the house. Won't start. I removed the supply line at the carb and gas shot into a catch can while cranking. Car will start if gasoline is poured into carb. Suggestions. The carb is a SOLEX.

-David

my76-280s · #2 07-18-2007, 02:59 PM

If I didn't supply enough info, please ask. The car is all original with 86k on the odometer. It was my fathers car before he passed away and very special to me. I am a newbie on the list and have a no start car in the garage. The gas appears to make it to the carburetor but that's as far as it will go. I'll try to answer questions about the car to help someone diagnose the problem. There must be a carburetor guru who knows the solex 4A1 like the back of their hand out there. Help?!

-David
'76 280 S

Larry Delor · #3 07-18-2007, 06:49 PM

Isn't there a filter right there at the side of the carb, where there is a filter? If you "step on the gas", can you see gasoline shooting in?
Does it start today? (maybe it was vapor lock the day it stalled).

my76-280s · #4 07-18-2007, 07:16 PM

Quote:

Originally Posted by Larry Delor

Isn't there a filter right there at the side of the carb, where there is a filter? If you "step on the gas", can you see gasoline shooting in?
Does it start today? (maybe it was vapor lock the day it stalled).

Thanks for the reply. It has been 2 weeks since the car started. At first I suspected vapor lock but it obviously is something else. I see no fuel filter, but gas spills out of the supply hose when I crank the engine. I thought I had a mechanical pump. Does it pump as the starter turns the engine over? I am not depressing the accelerator when this occurs. Gas gets to the carburetor but not into the carburetor. No smell of gas and the car will start when gas is poured down the carburetor. There are two electrical connections at the bottom front of the carburetor. Anyone have a clue what these are for?

tbenner · #5 07-18-2007, 10:15 PM

If you have fuel pressure from the pump and no filter between the pump and the carb it is likely the blockage is in the carb.

I am not familiar with that particular Solex carb although I recall some on my old VWs. I've had floats stick before on SU carbs (although they usually stick open and cause a flood) . If the car sat for a long time the rubber tip of the float valve may have stuck in the closed position after the bowl filled with gas. OR the passage may have gotten clogged with debris. The old school quick and dirty fix is to give the float bowl a rap with the plastic end of a screwdriver. If that doesn't get some gas moving you may want to drop the float bowl and have a look. You should have a look in there even if the screwdriver trick gets some gas moving.

Good Luck!

tbenner · #6 07-18-2007, 10:25 PM

These could be a fuel cutoff valve (to prevent run-on or dieseling). If that valve does not open you get no gas. That should be a cheap part if you can find it... just a selenoid. That would be a really easy fix. If the connections are part of something that looks like it screws in (like a bolt head) then that is probably what it is. When the ignition is switched on the valve opens and when you turn it off the valve snaps shut.

On an older car the connections could be just an electric automatic choke.

Can you let us know what it looks like where the connections attach to the carb?

my76-280s · #7 07-18-2007, 10:36 PM

Thanks for the post. The parts do look like they screw into the bottom front of the carb. Hard to see and reach. Will try to get a better look tomorrow. Will give the screwdriver trick a try as well. I like the fuel shut off theory! Hope to get her back on the road soon.

ctaylor738 · #8 07-18-2007, 10:57 PM

Crank the starter for maybe 10 seconds with the fuel line connected.

Then take the air cleaner off. Hold the choke open and open the throttle quickly while you look down the carb. You should see a squirt of gas from the little tubes in the primaries. If you don't then something is blocking the gas, since the pump is supplying fuel.

There is no magic bullet at this point. It could be a stuck fuel return valve - the thing on the fuel line with a vacuum connection, a clogged filter in the carb inlet, or a sticking float valve not allowing fuel into the carb.

I doubt that it is the idle solenoids. They shut off gas to only the idle circuit. They should not prevent the car from starting if you pump the gas a couple of times.

Good luck.

my76-280s · #9 07-19-2007, 11:39 PM

Thanks to all respondants. I crank the engine and no fuel gets into the carburetor. The two electrical connectors both receive 12v with the key on and click when connected and disconnected. Fuse #4 among other items controls the fuel cut off and carburetor heater and is good. The two solenoids #1 closest to the head says Pierburg 12956/2.5 and the other #2 says Germany 5248. They look the same size wise and connector wise. Both have two pin/barrell connectors. This is as much as I can see and read. They both click when the key is engaged. I suppose it doesn't mean they are actually opening and closing. I did rap them lightly with the back of my screwdriver. The carb would need to come off to reach these items.
The fuel supply line fitting has a thin screen which is clean. There should be a large filter somewhere. That's not it. Should the return line spit gasoline if gas doesn't enter the carburetor? I've now fouled up the rubber gaskets on the jets? or metering pins? using carburetor cleaner. This misinformed neophyte thought it would be a good idea to remove and spray these items as well. The cleaner destroyed the rubber gasket material. I've cleaned the primary and secondary inner surfaces and am nervous at the prospect of removing the carburetor. Looks like the Michigan get together is out of site for me.
Is there anything else I can look at before........omg what did you do!!!!

my76-280s · #10 07-19-2007, 11:40 PM

Where and what is a float valve?

ctaylor738 · #11 07-20-2007, 08:16 AM

The idle solenoids sound to me like they are working perfectly.

The float valve is at the front of the carb. It's connected, oddly enough, to brass float. As the level of gas in the float rises, it pushes on the valve and it closes, cutting off the fuel, then it drops as the engine uses fuel, the valve opens, and so on. Coming unhooked from the float may make it stick closed.

But you never did answer my question about the squirt from the accelerator pump. This has always been my health check as to whether the engine was getting fuel.

Sounds like you need to order a rebuild kit and buy a gallon can of carb cleaner and have a go at rebuilding the carb. Not as hard as it sounds.

Good luck,

tbenner · #12 07-20-2007, 08:29 AM

In general terms... the gas coming into the carb first goes into a float chamber or bowl. In this bowl there is a brass or plastic float. As the chamber fills the float rises (think toilet tank). There is a tab on this float that raises a needle as the float rises. That "needle" is 1/2 of the float valve. It is usually about 2 mm thick with a conical neoprene tip. The tip seals in a brass seat when closed (the other half of the float valve). If this is sealed shut no gas will pass. Others here will know this carb in more specific terms.

I am not so sure you can look in there while the carb is on the car. But I'll bet Chuck Taylor knows.

my76-280s · #13 07-20-2007, 09:33 AM

Thanks again for the replies. No squirt after cranking engine and manually moving linkage. I will try to locate bowl and valve and see if they are stuck. Can the bowl and valve be manipulated while still on the car? Is there a website that shows pictures of this carburetor with parts identification? I might not sound as ill informed as I am! Can I source the small o-rings on the needles? that I fouled up? The needles are long thin metal with tiny orifices that screw down into the carburetor?

-David
(Step away from the car sir and put that screwdriver down.)

ctaylor738 · #14 07-20-2007, 07:57 PM

Like I said, you need to source a rebuild kit to get all the pieces, seals, and gaskets. They generally include a parts diagram. They are readily available online, including from Partsshop on this forum.

I think you can find parts diagram at http://www.detali.ru/cat/oem_mb0.asp?TP=1. The Haynes manual on the "280 Twin Cam 123 Series" has a good section on the carb, as does the Mercedes 114 CD.

And, yes, you can easily access the floats and valve with the carb on the car.

my76-280s · #15 07-25-2007, 11:15 PM

Is it possible for the float bowl to fall off and into the carburetor. I see no evidence of anything under the choke plate where the gas would squirt out that looks like a float bowl. Should it be located under the venturi stacks? Gas should squirt out where there are two short funnel shaped pieces (venturi's?) with metal lines (jets?) in the side of it, right? I see nothing sitting at the bottom of the carburetor under the throttle plate. Where could the float have gone too? The primaries are toward the front of the engine and are smaller than the secondaries, right? Could the float be lying on the throttle plate out of view? Remember, the car has run flawlessly for 30 years and this problem started after idling the engine for 30+ minutes on a hot day, shuting it off and then attempting to drive away some time later. I made it two blocks before the car died.

For those with a 280s, 450 se,or sel, the black manual that came with the car (catalog B) on page 19 fig 1-152, group 07/1 is the float #30 and the needle #35?