w123 model 250 takes a LOOOONG time to start

[blankenship]

i've got a 1980 mercedes w123 model 250 with the Solex 4A1 carburetor. the car runs fine once started, but if you let it sit without running for more than a couple hours, it takes a very long time to start. it seems as if the fuel may have backed all the way back down the lines to the tank, and it takes a lot of cranking to get the fuel pumped back up to the carburetor. has anyone experienced this or does anyone know any tests or common causes? help would be appreciated!

 

[grober]

Is this starting difficulty with the engine hot or cold or both? Sounds like a problem with your fuel pump which I assume is a mechanical one? Some folks substitute a suitable electric pump as a test or as a permanent replacement to see if that cures the problem.

 

[ms500]

I have this problem too on my W124, it could be compression related or could be something to do with the fuel system.

 

[blankenship]

yeah, the problem presents itself when the engine is cold. it acts like it isn't getting any gas. i'm wondering if it could be related to the 'fuel return valve' possibly letting the fuel release all the way back down to the tank?

what would make you suspect the fuel pump? what would the pump have to do with the cold-start problem, and is that realistic even if the car runs great once started? if i spray a little ether/starting fluid down the primaries, she'll start right up...

 

[Dieselman]

If it's when cold it can't be the fuel pump as the carburettor holds a reserve of fuel in the float chamber.
It sounds more like an air leak or lack of choke, but it's worth checking the HT voltage as well.

 

[Frank O' Phile]

If it's when cold it can't be the fuel pump as the carburettor holds a reserve of fuel in the float chamber.
It sounds more like an air leak or lack of choke, but it's worth checking the HT voltage as well.

You beat me to the float chamber bit,

I assume it has an auto choke, can it be visually checked when cold?

 

[jaymanek]

from my experience i would say its the auto choke... I had great problems with mine on the old M115 engine...

I tried lots of different carbs and chokes but they all wear at the teeth, so when its cold its ok, when its warm its ok, just in between is when the problem occurs as the choke is not letting the correct amount of fuel in.

I would strip the auto choke down, observe where its sitting when the problem occurs.

 

[ali]

i've got a 1980 mercedes w123 model 250 with the Solex 4A1 carburetor. the car runs fine once started, but if you let it sit without running for more than a couple hours, it takes a very long time to start. it seems as if the fuel may have backed all the way back down the lines to the tank, and it takes a lot of cranking to get the fuel pumped back up to the carburetor. has anyone experienced this or does anyone know any tests or common causes? help would be appreciated!

Hi I have 1976-250 and exactly the same problem. Have you figured out what the real cause ?

 

[vijilants]

Its fairly easy on these to find out if it is a fuel or ignition problem but as said earlier doubt if it is fuel related as the car would have fuel in the float chamber to start it.

If you do suspect fuel, simply pop open the air-cleaner and spray some of the flammable carb cleaner down the carb whilst turning it over and the car should start and run on this stuff.

I would say look at the ignition system.....possibly a faulty condenser if you have a points / condenser setup. A weak spark even though there is a spark can cause all sorts of starting issues.

 

[Sp!ke]

I had the same problem on my LWB 250.

Fine adjustment of the manual choke assembly by my mobile mechanic friend with a penchant for old Mercs solved the problem. He ended up buying the car he loved it so much.

 

[jaymanek]

He ended up buying the car he loved it so much.

I did wonder what happened to it!

 

[kalseddon]

where is the auto choke

 

[jaymanek]

Bolted to the carb, has two coolant pipes to it (in and out) and a two pin electrical plug, its in several sections... the wound up coil which works by coolant temperature and then the stepper arm and piston which control the choke...

Mine used to seize up until I took it apart properly one day and sorted it out.