engine trouble

[eddie007]

hi, just recently bought a 1968 250se 4door and the engine runs for a few minutes then cuts out I think its running to rich. any ideas how to adjust. much appreciated

 

[Eric Alex]

Hi eddie007
Did you manage to sort your engine issues?


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[eddie007]

not as yet

 

[estate-agent]

Is this fuel injected or carburettor?

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[Ted]

SE will be injection.

 

[estate-agent]

I have no practice on a Merc of this age but I guess it has Bosch's old Jet tronic mechanical injection which can be plagued with idling problems generating from the pressure plate, mixture screw, cold start injector etc.

I haven't worked on a car with Jetronic for at least 20 years but I still remember, rough idles through vacuum leaks, dirty pressure plate, fuel leaks etc.

If you have no way of measuring the engines CO mixture then I would suggest finding a local garage where they can check emissions for you.

If you need to get it sorted at home with no access to checking CO then it will be a case of trial and error. If its fine cold but starts to stall once warm then start with basics, Idle speed screw, if it still fails to stay running even with idle screw ramped up then personally I would pull the spark plugs and see if they look sooted up black. Spark plugs change colour very quickly so shutting it off while its idling lumpy may give you a good indication of fuelling at idle. If they are very sooty then its a good indication of the enriched mixture you are concerned about. If I remember rightly the mixture screw is on top of the fuel distributor and it is down a thin tube, this only takes very slight turns to change fuel mixture and it also takes a few second of running before it settles down so if using a CO meter you'll need to wait for it to register the change in fuelling, you should notice the difference in engine speed if you can keep it idling whilst you adjust the mixture screw, anti clockwise to lean, clockwise to enrich.

Another thing that is easily dismissed or in fact not thought about is the crankcase emissions, if the engine has been running excessively rich then bore wash will likely have allowed a small degree of fuel into the sump oil, the crank pressure that is usually directed back into the intake (via rocker cover to inlet manifold or rubber intake hose) can act to enrich the mixture quite significantly, especially on older cars. Removing the breather pipe from the intake track can lean off a rich running engine, I used to have old high mileage cars come for MOT's that failed on emissions, removing the breather from the intake used to lean some cars off so much that they idled better and passed the old 3% CO emission requirements. If this did turn out to make a difference then a fresh oil & filter will resolve that issue. To try this test you will need to cap off the intake pipe inlet that you remove the crankcase pipe from otherwise it will introduce a vacuum leak and make engine stall, rev up or hunt uncontrollably.

If you have already tried these things then forget all the above. Been so many years since touching on any issues like these and have been out the motor trade for many years too.

Hope it is of some help though.

Also where are you based? May know someone in your area who could help.

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[eddie007]

thanks very much ill give it a go next week