Pierburg Carburettor - Does it have a return spring?

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H

harry_lalli

Member
Joined
Dec 29, 2009
Messages
58
Location
Birmingham, UK
Car
2012 C63 Estate | 1972 W115 220/8 - White | 2000 VX220 2.2 Supercharged
Afternoon,

i have a question about the carb currently in my '72 W115. Its a pierburg/stromberg carb (175 CD)...but the accelerator pedal stick to the floor when fully pressed. Just wonderng whether there should be a return spring as it seems to come up ok when lifting it by hand....not the wisest thing to do whilst driving though :eek:

have only had the car a few months, been getting some welding done, only just noticed...

any ideas? if it is a return spring, any ideas whether its available as part of some refurb kit? don't really want to resort to using elastic bands :p

Thanks people :thumb:
 
Pop the ball linkage off near the carb and see what happens.

There is a spring on the butterfly valve on the carb that spring shuts the butterfly valve and that should also act against the linkages.
 
This is virtually the same carb as on Volvo 245, and yes there's a spring on the outside of the throttle. If the butterfly snaps shut then it's the cable. Probably the cable anyway.

These is or was a re-furb kit. Some bits cheap, others very expensive (thermostat valve thingy). Re-con may be an option if available. But the carb is solid and reliable so prolly only needs a bit of cleaning.

You have to show an MoT garage how to adjust it for emissions 'cos they ain't got a clue and will mess it up ;-(
 
jefrs said:
This is virtually the same carb as on Volvo 245, and yes there's a spring on the outside of the throttle. If the butterfly snaps shut then it's the cable. Probably the cable anyway.

These is or was a re-furb kit. Some bits cheap, others very expensive (thermostat valve thingy). Re-con may be an option if available. But the carb is solid and reliable so prolly only needs a bit of cleaning.

You have to show an MoT garage how to adjust it for emissions 'cos they ain't got a clue and will mess it up ;-(
Click to expand...


Interesting! Yes I have a Pierburg 175CD on my old 244. The so called Volvo specialist I used to take it to for MOT used to mess it up every time. It would go in running perfectly sweetly and giving a good MPG and come out hardly running at all.

I now take it to a kinda back street garage where the chap really knows what he is doing and it always come out running perfectly (and with incredibly low CO etc - about 10% of the max limit for MOT).

For future reference in case this guy closes up shop or whatever what is it that one needs to do to adjust these correctly?!
 
With the Volvo, one chap actually unscrewed the blanking plate that was there for a solenoid valve (aircon compensation n/a) when he couldn't find the air screw next to it, and had not the slightest clue about the main jet adjuster underneath.

The main jet adjusts mixture and the air jet (bypass) adjusts idle speed. The base idle speed is set to a specified gap on the butterfly (use a drill bit) by bending the throttle stop (do once & forget). Adjust cable so that throttle shuts right down, never set idle on the cable, and full pedal equals full throttle. Warm engine and perhaps increase idle on the bypass. Screw the main jet in until it hunts then out half a turn, slow the engine down on the bypass and do it again and again until it sounds right (which is why it's called "tuning"). If you get a flat spot on acceleration then the jet has to be lowered out a bit to enrich the mix a little, which will raise the idle...

The cold start "choke" needs a bit of a fiddle on its cam to ensure it is off when it is off and only raises the idle until about halfway (fast idle), then enriches it for cold starting.

The carburettor is right about 98% of its range, unfortunately the CO machine is used at idle where the mix usually has to be a bit rich if the motor is to run smooth and efficient. The bypass screw can leak, and need a new O-ring, eventually mine had about three on there.
 
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This is useful info, thanks very much.

If only Mercedes would have fitted fuel injection to the OP's W115 or my old Volvo things would probably have been simpler! Odd that both FI and carb were available in the same years and on the same engine in the Volvo - the FI version benefitting from about 30% more power too!

Must have been cheaper for the manufacturer to stick in a carb!
 
The PI version of the 2.3 Volvo was not that much more powerful about +15HP but it had a narrower power band. The Volvo 2.3 was a lazy big lump of an engine, actually half of a 4.7 litre V8, only a few Volvo 282 (model 2, 8-cly 2-door) coupes were produced. A similar carburettor was used by Ford at the same period. The Volvo 240 followed on from the 140, a carb was traditional, and fuel injectors not entirely reliable then.
 
Had no idea about the 282, that sounds awesome. I feel a 4.7 transplant coming on!! Assume the only other use for the 4.7 V8 Volvo at the time would have been in commercial vehicles/boats?

My 2.3 is unlike any other car I have driven, massively torquey at low revs (but not much going on over 3.5k)- more like a diesel than a petrol.

Sorry for the thread hijak, not to mention non-Mercedes talk!
 
I believe the 2.3 L Volvo was originally half of an American V8 (Chevvy small-block?) i.e. built under licence much like SAAB did with the Triumph Dolomite/TR7 engine. I've a feeling the 282 coupe was only built as a show car for exhibition, very few of them and not on normal production lists, no idea which vehicle they took the engine from: boats and trucks use diesel. I saw pics and article on 282 in the local Volvo dealership. I reckon they lost the plot because the V8 would have suited the work-horse estate better than some sporty model. My 245 finally died after being struck by a circus' ERF tow truck, it was still drivable but BER, so I had to get another big estate, hence MB E320 S210.
 
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Hi chaps,

just a quick update, managed to find the spring it was the one on the carb, thanks for the help...although now i have other question (apologies in advance for my lack of knowledge)

car runs, idles high on occasions seems to settle once warm, guessing this is the autochoke? anyway...had a service on it recently (the car, they looked at the carb) said idle speed compensator was jammed/not operational...and i already knew but the diaphragm could do with a change....

by carb is a lot like this ... (red cap instead of yellow)
l_3db08a91b9bde8223b634f75295bed17.jpg


any idea where i can get a refurb kit for this? (pierburg 175cd) and also where is the mixture screw for fuel? is there also one for idle speed??

thanks in advance guys, trying to get my car ready for my wedding so have just over 2months to get it running right.

bye for now.
 
evening/morning guys,

had a quick play on the carb after reading those links (v good material, thanks!)

next question for you knowledgeable folk
gallery_11826_133_93107.jpg


Whilst looking at it i noticed something that seems to come out from under the carb...not sure what it is...is it a sensor (red arrow on image) where does it go? It seems to have been wrapped around something to keep it out the way, mustve been local mechanic when they did the welding...

any thoughts on where it should go? Car still starts and drives so this must have been disconnected for a while.

thanks for the continued help/support!:thumb:
 
Looks like a bit of the idle speed shut off valve which functions to momentarily electrically switch off the fuel to prevent " running on" This was a phenomenon on older cars with low compression/low octane fuel/ retarded ignition[ relative to modern settings] which meant the engine would still turn-over/fire after the ignition was switched off. Not strictly necessary and may have been removed/ modified by the previous owner--- not sure from the picture tho- might be something completely different.:dk:
 
Thanks for taking a look grober, i wasn't sure if it was something to do with my idle running speed problems...it comes out of the bottom of the carb, page 2 on this doc http://mb.bolinko.org/wis/w123/CD01/...15/072-090.pdf is the item/part in question, but it does actually show/say what it is.

Next step is to order a new diaphragm...and get that changed. Thanks for your continued support guys, the merc is on course to make my wedding! :)
 
OK difficult to see from the picture you posted and without being able to check for the presence or absence of certain components but maybe its the vacuum operated fuel return valve which is supposed to prevent vapour bubbles forming in the fuel system when the intake vacuum is too high- presumably sucking fuel from the fuel line more than it should. It would appear to divert fuel to a return pipe via a diaphragm operated valve -- at idle or when the throttle plate is closed [ the vacuum control line inlet is then exposed to the "suck" of the engine. Once the throttle opens that vacuum disappears as the throttle plate passes by the inlet and the vacuum disappears - the fuel bypass is shut off and fuel line supply to the carb ceases to be bypassed. Its possible the fuel line has been attached directly to the carb fuel inlet and this unit bypassed altogether This would still mean the carb would function but might mean slight fuel starvation at idle as the fuel line is "sucked dry" by the engine vacuum.
My guess is you need a new fuel return valve or its diaphram followed by a bit of replumbing of the inlet lines. You should also check the return line is clear- by gently blowing down it with an airline. You should hear bubbling in the tank if its OK.
 
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Afternoon MBClub,

Thanks for the continued support, I noticed a rebuild kit on the internet for a stromberg 175 CD, The Carb I have is a Pierburg 175CD, assuming its the same one, so is this the rebuilt kit I need? link here

Thanks guys.
 
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