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I have a 1991 Volvo 1.7 with a worn Carb. and on limit of emission rating with no further adjustment available . Anyone have any bright ideas? Existing carb is Solex twin barrel downdraught Code 28/34 CISAC Z-10.
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Firstly make sure all the breathers are clear inc. pipes the breathers connect to. These can block which results in poor engine running and in some cases high/low emission readings. There is a carb company called carburettors.co.uk ( I think that's right )who supply repair kits for reasonable price and speedily
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I would also check that the float level in the carb is not too high as the level tends to creep up with age in my experience.
Also check that the main air compensators are clean (long needle like screws under carb top).
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Have you tried assuming you have the tool
screwing the co/mixture control in as far as it will go.
But remember from where you started.so as to go back to it
if the engine stalls fine.If the engine runs on but with a bit of uneven running.may be the co/mixture control is faulty in which case a recon carb is needed.but if it stalls the problem lies possibly in what has been said before
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Don't be too hasty in condemning the carb. Lots of other things have to be spot on too.
Vacuum pipework, any vacuum-operated devices, connection orifices, flame traps, engine breathers, engine oil, ignition, air cleaner, throttle body, anything else you can think of.
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Assuming that the mixture control screw is allready screwed into the maximum, and the idle CO level is still too high, I'm not sure how this would help..if this control was faulty it would most likely be caused by dirt and should just be a simple case of removing the screw and blowing out the passages in the carb body etc.
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The mixture control screw should not already be to max
it should be approx 1.1/2 turns from the closed point
the more it is unscrewed the richer the mixture becomes
the screw valve can become worn by the constant passing of petrol.it is not uncommon on old carbs.
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Whilst agreeing that all the forgoing points should be checked first, I remember having a problem on an earlier 1.7 with Solex carb where the water heater on the carb body had been unfixed by a previous owner, (a single screw from memory). When I refixed it it was impossible to set up the carb correctly (too rich)! My logic says that this is the wrong way round, but it may be worth trying if all else fails.
I do not have access to a manual at the moment, but is there something on this engine that says only set it up when the electric cooling fan is running? (I may be confusing it with another car?).
Also try taking out the air filter element (or checking that it is not clogged with dust or oil).
pmh (was peter)
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That may be because the water heater was connected to the choke
so any adjustment made to co would have been incorrect.your
second point is correct.Co should not be altered untill engine is at full working temp ie fan has worked once or twice.taking out air filter element is not a good idea.Leaves room for any dust ect to enter carb/injector system.which may cause other damage.checking whilst engine not running ok.but not while it is running.
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If the car is reaching the point where significant spend on the the carb is needed to get it to meet MoT emmissions standards, removing the air filter may allow it it to get a a pass. I agree long term running is not necessarily desirable, but it is better than throwing the car away! It could also be a way of identifying that the filter is clogged and requires replacement.
If I remember correctly the fan running made a significant difference to the CO readings. I can only assume that the electrical load on the alternator affects the engine speed sufficiently to alter the airflow thro the carb, with a subsequent non linear change in petrol volume hence a change in mixture. Mine old 340 was a potential scrapper so fixes (not solutions) were the appropriate answer!
pmh (was peter)
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from first post all that was said is carb close to limit.
if air filter was the cause would have or should be first
item to check.in what you said the air filter be removed will only make a difference if it is clogged.
The fan running will not make a difference.It only says engine
has reached max temperature.And of course prevent overheating
there wasn`t enough info given on first post really so best wait for further info
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I don't think wear of the 'screw valve' is as issue here. Wear of the tapered mixture control screw by the passing petrol/air mixture would be very minor and easily taken up by a small adjustment. Certainly they can become damaged by screwing them in too tightly but this would seem unlikely to be the problem here. Any fault with the slow running is most likely caused by blockage in the idle air bleed/jet or carb flooding.
The problem seems to be that the mixture CO is too high despite the mixture control being screwed fully in (max lean setting).....as previously stated, it should be approx 1-1.5 turns from the seated position.
It could be worth removing the air filter to check that the choke (presuming it's an auto) is fully off when the engine is hot and stays off when the engine is revved.
A rebuilt/new carb would be a waste of money.
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could be I did not explain.I only said that so as not to complicate.>>Wear of the tapered mixture control screw by the passing petrol/air mixture would be very minor.unless I am mistaken it is a concern as it provides the total mixture control.to the carb.the fact it is I.12 turns i did mention
before.the fact I did say screw valve should have said it all really.But have to admit should have been clearer.
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Hi,
My Escort has a similar problem - although not at critical point yet. It has been suggested to me (and I don't really understand carbs so don't take my word on this - but it might be something to investigate) that a smaller main jet and a larger air corrector jet may help.
(Whatever the heck that means :-) )
Cheers,
Mark
(Interested in an explanation of this too, if anyone feels the urge! :-) )
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This is something worth considering. Carburetted vehicles are usually set up rather rich because it's an easy way for manufacturers to comply with NOx emission regulations and gives very slightly more power. Result is poor fuel economy.
A larger air corrector will lean off the mixture higher up the rev range and reducing the jet size will lean off the mixture through the whole rev range. Personally I would reduce the main jet by from say 95 to a 90...you could go further but might find that you get flat spots....I fitted a smaller main jet to a 1.8 sierra a few years ago and noticed no loss of performance.
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