tell me my spark plug condition!

SilverSaloon

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hi

i recently changed the spark plugs on my 1985 280SL. these plugs were sooty black so i weakend the mixture slightly as previous owner also said he had made it richer....

new spark plugs, about 700 miles on look like this:

SL001.jpg


SL004.jpg


So what does this tell you? is it too weak, rich, or just about right...?

thanks!

Derek
 

television

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I say still a bit rich and black,,but hard to tell unless the car has had a run and come off cold start
 
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SilverSaloon

SilverSaloon

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I say still a bit rich and black,,but hard to tell unless the car has had a run and come off cold start

yes car always gets the change to get to normal temp - about 40 miles a day when i use it (a few days a week) and also had a good run 500 mile round trip.
 

turbopete

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as Malcolm suggested, id say a bit rich still, although not massively so. id prefer to run slightly rich than too lean anyhow as too lean a mixture can cause detonation (pinking) which isnt good for your engine. the best solution would, of course, be a proper tune up.

incidentally, the mixture setting should only affect the fuelling on idle. once above tick over, the fuelling is set by other means like jets in a carb or ecu on an EFI engine. cant remember about mechanical injection, but i THINK its to do with the fuel distributor/fuel metering unit
 

television

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as Malcolm suggested, id say a bit rich still, although not massively so. id prefer to run slightly rich than too lean anyhow as too lean a mixture can cause detonation (pinking) which isnt good for your engine. the best solution would, of course, be a proper tune up.

incidentally, the mixture setting should only affect the fuelling on idle. once above tick over, the fuelling is set by other means like jets in a carb or ecu on an EFI engine. cant remember about mechanical injection, but i THINK its to do with the fuel distributor/fuel metering unit

On the only 280 SL that I have worked on, we had to set it a little on the rich side to get overall good running, as soon as it was set a touch weaker the idle was very poor so as is could be OK
 
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SilverSaloon

SilverSaloon

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i weakened the mixture and also turned up the idle screw to get good idle that is now ~700rpm at idle in D. and about 800rpm in P, which Haynes suggests is correct. i did this mainly because of the dark black on the old spark plugs and also that the previous owner said he had richen'd the mixture "a bit" for my long journey back to scotland.

idle is nice and smooth and car is running great

car passed MOT last week and was fine on emissions, slightly better reading than year before. different test stations though.....

i would like to get the mixture set correctly and will keep trying to find a garage to get this done, who knows what they are doing, which is my worst fear.

i'm hoping cant be that bad considering the above points....
 

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Sounds good to me..my Bosch book says 800rpm

The given figure is 1.0, +/-0.5%
 

harpersimon

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I have always had a look here for good guidance. Yours don't look anywhere near as bad as 'bad' plugs so maybe some small tweaking only!
 


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