1967 250S - Poor starting when engine warm

[Anonymous]

A friend has a LHD 250S saloon 1967. Recently the mechanical fuel pump was replaced with a mercedes electric one. Now he finds that the car starts easily first time when cold, but after being driven for 10-20 minutes and turned off, the engine will not restart. After a long period the engine will restart because it has cooled down. Sometimes it can be started when engine is warm if the throttle pedal is fully depressed and held down and starter cranked for 15-30 seconds. Any suggestions as to what might overcome this problem?

 

[Colin Tigwell]

1967 250S

This car should not be hard to start, we have a 1969 model, which I understand is the same model.  Ours will always start first go, irrespective of how long it has sat.

Is there a reason for putting the electric fuel pump on, I have always been reluctant about changing cars away from standard.  

I jusr wonder if the electric pump, is allowing the fuel to drain back, and so the engine does not start, because of poor fuel flow.

Never been a lover of electric fuel pumps, ever since my first car, a 1952 Morrie Minor.  At one stage the pump was so unreliable, that I would not venture out, unless I had a passenger to kick the firewall when the pump stopped.

Eventually found an old timer, who taught me how to set the points up correctly, and then all was well.

The problem I have found out over the years, that sometimes problems start, when something is done, and you think that action, has caused the problem.

The best advice I can give, is work through the problems one by one, do not do them all at once, but check the fuel first, perhaps doing a pressure test on fuel flow, then checking the electrics, could be something as simple as a point change, coupled to a condensor.

But try and rule each problem out, in a proper manner, otherwise you can spend much time and money, and never understand what the problem was.

Regards

Col Tigwell Downunder

 

[Andy]

1967 250S

Hi All

If its a 250S then its fitted with carbs. Sounds like they are running weak. So the mixture not rich enough till the engine gets cooler and the mixture a little denser. Suggest you get the carbs set up and make sure the general engine tune is ok. Points etc.

Regards

Andy @ www.mercedesservicing.com

 

[Anonymous]

1967 250S

Hi Colin and Andy.
Thanks for replies, and sorry for very delayed response but have been away in the wilds of Wyoming.
Apparantly the car has had two new fuel pumps. The first replacement was a standard mechanical one and the second was the electric one. It seems that the garage (a Merc specialist but not a registered dealer) have concentrated on the fuel pump and not on the other ideas you both raised. He is taking the car back to them for  further checks on fuel pressure and carb tuning. Will let you know outcome.
William