Stromberg CD175 mixture adjustment.

[samuelsmiles]

Hi all. My W123 is running really rich - spark plugs getting a coal like covering, strong smell of unburnt fuel etc.

I was told the adjustment screw for the fuel was within the circled area highlighted below which would appear to make sense because of the RICH marking, but there is not one in there?

The picture at the bottom is for the air adjustment, would the screw I've highlighted be correct?

Any tips would be appreciated - its a bugger finding a mechanic interested in this sort of old stuff and I'm quite happy to get my hands a bit dirty.

Thank you, Chris.

.

 

[optimusprime]

mixture

Sam i had a pair of Strombergs on my Triumph 2000 you adjusted them though the oil chamber in the top ,it was a long allen key made for the job. Try a google on it. I will find out for you.

 

[optimusprime]

rich

Sam i was right the red cap as to be removed ,then a long allen key is put down inside , you turn clock wise will make it weak ,anti clock will take it up to make it rich. Mind the diaphram in side mind you dont damage it. Loads of information on Google.

 

[Dieselman]

The screw you circled is the air bleed to adjust the idle speed.

As an aside, I once came across a Stromberg that had been made from two halves.
The lower half had the later fixed jet, the upper half had the earlier fixed needle, so no adjustment was available.

Until Mr Hammer made and appearance on the underside of the jet...

 

[samuelsmiles]

Many thanks, I can't find the tool/allen key after a quick search. Can you give me any links? I'm in the UK.

Best, Chris.

 

[grober]

Think this may be what you need but check with the supplier that its suitable for your carb.
Moss Europe, Ltd - Classic Parts for Classic, MX-5, MGF, Mini, MGB

 

[samuelsmiles]

Hi, I found this adjustment tool in a local motor factors. A Franklin tool (TA25) for post '78 cars (mine is an '81) which has a slotted fixture attached to the allen key. I've very carefully tried to engage the tool but it doesn't seem to want to locate properly - maybe it has an earlier carb and needs the allen key tool as in the link from optimuseprime?

Chris.

 

[optimusprime]

info

This one is not like mine. Keep hanging on to this post i am sure someone as done this before, so come on lads.Can anyone help.

 

[henley]

The mixture adjusting tool shown on grober's photo is the only one I have seen and used. The outside collar with the small key way button is to locate the diaphragm stationary and stop it turning the diaphragm (can damage) while turning the centre mixture needle adjustment allen key. Anti clockwise for richer, clockwise for leaner mixture, its was usually quite tight to turn also.

 

[optimusprime]

henley thats the one i had for my Triumph 2000,or very much like it .

 

[samuelsmiles]

Thank you for your answers. I'll get the allen key tool linked by grober. (or saw off the collar on the tool I have)

Chris.

 

[jaymanek]

mine was adjusted from the bottom... from vague memory there was a nut to loosen off then the mixture was adjusted by turning the fitting at the bottom.

But the Stromberg 175 was made in various versions, all slightly different.
I know as I have a bucket full of them somewhere from the times when I was attempting to get my M115 running right.

 

[Dieselman]

mine was adjusted from the bottom... from vague memory there was a nut to loosen off then the mixture was adjusted by turning the fitting at the bottom.

But the Stromberg 175 was made in various versions, all slightly different.
I know as I have a bucket full of them somewhere from the times when I was attempting to get my M115 running right.

Early ones were bottom adjustment, but due to the risk of leakage the adjustment was moved to the needle.

I've had an SU leak petrol onto the exhaust manifold, but never had trouble with Stromberg CD175, other than split diaphragms.

 

[grober]

http://www.howacarworks.com/fuel-systems/adjusting-a-stromberg-carburettor

 

[bolide]

I think that, rather than adjusting the mixture, you should be asking why it needs adjusting

Nick Froome

 

[llewe]

Because its old, because the needles wear, because it might have been fiddled with by some previous owner....that said 90% of carburettor problems are electrical so ensure that timing , points, plugs, distributor cap, leads etc are all tip top before carb tuning-oh and if tappets are adjustable on this engine, that they are correct. Also that the air filter is clean. Best to use a colourtune plug or co gas analyser to accurately check/adjust when you get to that stage. Oh and sooty plugs could be oil burning too.

 

[llewe]

Also looks as though that you have an automatic choke mechanism in the dome with the heater hoses connected , make sure that is operating correctly, they were notoriously unreliable on many cars of that era- aftermarket manual conversions were popular back in the day- This may of course not apply to the superior engineering of Mercedes

 

[grober]

LINKS HERE MIGHT BE USEFUL
http://www.mbclub.co.uk/forums/244106-post2.html

 

[KeithJG]

All this type of variable jet or constant depression type carbs. went out of tune mainly because of engine vibrations and not much because of wear as it does take a lot of fuel and miles for them to wear but at least they are adjustable when wear does happen.

The pic. of the choke mechanism look in the correct place as there are marks or dents that one has to line up before the single nut is tightened to hold in position......the choke is adjustable for warm/cold winters by turning the choke mech. to the left or right before tightening the centre nut but as said the normal is where the dents line up.

It is best before taking off the dashpot where the diaphragm is and clean the needle holder with metal polish so it`s smooth and it will fly up and down quicker giving instant pull away when driving as the dashpot and needle fly up quicker so better response. The dashpot piston should be topped up with 3 in 1 sewing machine oil as this helps the quick lift before the damper is screwed in but only to the top of the shoulder.

The jet through which the needle goes should be flush with it`s shoulder inside the alloy casing and should be adjusted so.

When assembled usually the starting place to enable the engine to start is 2 full turns up from the base position........there will be a pin to lift the dashpot 1 mm when idling and the revs should just rise and die when mixture is correct if it rises and stays it is too rich and if it just dies is to weak.

The air idle control screw usually lies between 1.5 to 2 turns out from fully screwed in.

 

[samuelsmiles]

Thank you for all your replies - it isn't a major issue so I'll leave the carb alone until I have the timing, auto choke and other stuff checked over.

As an aside, inside the air filter housing intake pipe, there is a flap mechanism attached to a long spring that, I'm guessing, controls the amount of warm/hot air coming off the manifold and the cold air coming in to the air filter housing.

I've had it off to check it over and the flap just seems to loosely flap about. How exactly does this mechanism work?

Best, Chris.