Correct in suspecting IP check valves?

[jedwards]

Back home from my recent travel so now keen to resolve my cold start problem.
Firstly, before the car was delivered to me, it apparently had the common gelled fuel problem caused by extended underuse.  The tank was removed and cleaned, the fuel pump overhauled.  When it arrived, it ran fairly well when warm, but started poorly.
Subsequently I have dismantled,  cleaned and checked the CSV and WRD are functioning properly during cranking and that the ignition and fuel flows are correct. I have done the linkage tour, corrected the usual issues, upgrade the ignition and set the timing to Dr Benz recommended settings.

In spite of this,  she still requires around 4 to 6 seconds of cranking when cold before it will catch. It then stumbles for another few seconds, often stopping.  Much better on the second cranking. Once it starts, it is OK and runs perfectly when fully warm.  Starts perfectly when warm.

I have read that old fuel gunk can become trapped under the IP check values, causing them to leak back leaving no fuel in the injector lines.  Letting the pump run for a while before cranking does not seem to have any effect and as there is  no apparent change in pump note to indicate a loss of fuel line pressure, I do not believe the problem is on the supply side.

Am I right to suspect the IP check valves, in light of this evidence?
Is there anything I have overlooked?

Jeff

Attached a couple of images in her in her rarely needed "formal attire" (hard top on).

[ja17]

Hello Jeff,

Sounds like the check valves may be your next step. Did you check and clean the fine screen in the inlet fitting of the CSV?  The get clogged. Also is the enrichment solenoid on the injection pump working? 

[jedwards]

Hi Ja17,
Yes, I have completely disassembled and thoroughly cleaned and checked the CSV.  The Solenoid is working properly and is moving the rack.
I believe the CSV is providing the first pulse of fuel that helps its catch, but once cranking stops and the CSV shuts down, the car struggles to get enough fuel to keep it going. That is why I suspect the injector tubes may be empty and requires time for the the IP pump to bring the empty tubes up to pressure. The fact that it starts much better on the second cranking seems to support that idea in my view.

Can you advise what is involved in cleaning these check valves? I have read how to make a tool to remove them, but there does not seem to be much information on what to do then. How should I go about cleaning them? Can I test that they are working before final reassembly?
Jeff

[ja17]

Hello Jeff,

They are a basic kind of spring and ball check valve and do not come apart. I have never tried to clean them, but I suspect you could move the ball and try to flush some air or solvent through them?

Sometimes just installing the  new seals around them helps the problem.   

Might not be a bad idea to check your system fuel pressure and do a spit linkage mixture test on the cold engine at start up. Any lean running situation could agrivate the cold starting.

[jedwards]

Hi ja17,
Mine is an early 250SL, so I have the needle and seat type check values,  identical to the type used in the CSV.  There was  bit of contamination on the shoulders, so I polished them and seated them as best I could.  I also took your advice and again stripped down the CSV testing it in situ, rather than on the bench.  It was giving a rather weak stray, so I pulled the nozzle spray head off the delivery tube, soaked it for a few hours in white spirit and blew it back using an aerosol carbi cleaner. I then got a really good strong spray from it.  Not sure which did the job, but this morning it started perfectly!!!

Now I only have one remaining start issues to sort.
Firstly, why it stumbles so badly after it first starts and takes at least 10 to 20 seconds of running at idle before I can touch the accelerator without it stalling.
Secondly, why it is running rich during warm up even though all the shims from the WRD have been removed and the WRD breather is working perfectly.  Runs perfectly as soon as its gets even slightly warm.
All seems to point to excessive  richening of the rail by the WRD that is corrected as soon as it warms, but as i said, I have no adjustment left. Only option seems to be to remove shims from the BC to the lean the entire rail and then try to re-establish good warm running by playing around the IP screw settings.
I'd live with the excess richness during warmup (as its only for a short period) if I could just solve the stumbling immediately following start-up.

Any thoughts?
Jeff

[ja17]

Hello Jeff, 

Ok, so you have the cone type check valves.  Dirty injectors can dribble gas after the engine is off, leaving the fuel injection lines partially empty of fuel. You may want to check them also.

[tel76]

Hello Jeff,
I hope you resealed the jet nozzle to the delivery tube, if not it could come loose and enter the engine ,you would not be happy. :'(