Warm Running Device-71 280se

[mbgingerbread]

The warm running device is slow to close. On startup the filter indicates air flow. The engine runs unevenly until the vacuum is reduced by the closing of the piston in the WRD barrel. I made an attempt to clean the WRD and used a bead blaster to clean the moving parts. I also replaced the thermostat-checked to make sure it would open by immersing in hot water. I was also careful to bleed the air from the coolant lines at the WRD. My question is simple: are the tolerances so close in this device that any thing I've done hasn't made any difference and I will need to buy a new one or find a good used one?
Thanks,
Turner

[mercmad6.3]

It is very close.
Chill the brass thermo in the fridge for about 20 minutes to get the temp below 20C. measure the length of the thermo.
Then with some boiling water on the stove,check the water temp. it wants to 80C. Immerse the thermo by dangling it in the water on a piece of wire. it doesn't matter how long it's in there for, about 5 minutes should be sufficient.

measure the length again.
if it has moved completely it's OK.
When checking the injection,always do the basics FIRST.
A perfect ignition and valve lash are more importantr than messing with the injection.
You should also have at least two sets of plugs handy. You can quickly clean sooty ones and replace the plugs to ensure your engine is running properly and not just missing because of fouled up plugs.

[mbgingerbread]

I checked the thermo and the shaft extented fully. The timing is spot on- 3 deg atdc, vacuum advance connected, engine warm. When the engine warms the misfiring stops because the air the intake is receiving shuts off with the closing of the WRD piston?
I can only imagine that I will have to replace the WRD as the barrel fitment has probably been compromised resulting in a slowed piston movement.
Would incorrect valve lash result in rough running until reaching engine operating temp? The problem I am having is consistent and other than some valve train noise at idle the engine runs smooth and has good pickup for its age.
Thanks,
Turner

[mercmad6.3]

Valve lash plays a very important role in engine performance,more so on the OHC engines.
But,normally over tight valve clearance only shows at running temp. Your misfire on a cold engine is different.
IS it a constant misfire or does it only happen when the engine is revved up?
if it only happens when the engine is cold and being revved,it is too lean on warm up.
You describe the plugs as being fouled so it sounds like the thermo is adjusted to a very rich at start up condition.
The length of the thermostat is very important hence the table i posted above.
Under the thermo is a little bolt on top of a piston,as the thermo pushes down it leans out the mixture. I would say the bolt is screwed down too far and needs to come one turn or until you get a leaner mix on warm up.

A slow thermo stat ( never actually seen one) would only make a hot engine run rich until it closed off the excess air.Check that you are getting flow through the hoses,no flow also causes rich running.
In the above post you can see how the thermo stat settings are arrived at.
You now need to check exactly when the thermo is closing,too soon or too late and adjust the mixture either way at the thermostat Only,not the pump idle mixture.
When running correctly,these engines can be started instantly from dead cold and will perform perfectly from cold without any thought of flat spots etc .

[ctaylor738]

Good advice from Oz. My .02 -

I have the same problem on my 230SL. I believe that it is caused by the warm-running device allowing extra air, but not extra fuel, causing a lean mixture when it should be rich. I verified this with my CO meter.

I don't have have the stones to go into the pump and try to fix this, so I am living with a lumpy idle for the first 30 seconds after starting.

Three things helped me, though.

- Make sure that your cold start valve is actually working by taking the whole assembly out and reconnecting it facing outward. Put a plastic bag over it and crank the starter and make sure it squirts. Mine was getting power correctly but the little jet inside was plugged. The extra fuel has improved starting and idle right after.

- Check your warm idle and adjust the air screw to get it as low as possible. The reduced air will give you a richer mix for warm-up.

- Check your warm idle CO to make sure you aren't lean.

You can also try removing the little air cleaner and plugging the opening to remove the extra air.

[mbgingerbread]

Finally getting around to a settlement of WRD.
Checked the cold start valve-good spray pattern from nozzle fitting. I have a spare and replaced the existing C/S valve-slowly realised it wasn't much good and put the original back on. Decided to follow a hunch picked up from one of A. Dalton's posts. Checked the position of the spacer between the end of the thermo and the plunger which rests inside the Injection Pump. Reversed the position-top to bottom (old position) then bottom to top. I noticed that there was an increase of spring pressure when I re-installed the WRD as the plunger contacted the fitting inside the IP.
Started and ran smoothly-no more rich exhaust!!!
Turner