Mixture Screw Solex carb

Post by **Tim Leech** » Sat Jun 04, 2011 10:39 am

Can anyone remind me to richen the mixture on a BX 16 with a Solex carb do you turn the screw clockwise or counterclockwise to enrichen the mixture, also its exact location?

My 16TRS is running a but too lean (MOT gas test) and is rather "flat" and needs tweaking up slightly.

Thanks!

electrokid · Post by **electrokid** » Sat Jun 04, 2011 11:18 am

Carb settings usually remain correct - if it seems it needs adjusting it's usually something else that's going wrong and adjusting the carb is lilkely to be covering up a problem that's developing elsewhere.

Best to check everything you can think of before fiddling with the mixture - air intake / filter / warm air feed from the exhaust pipe; fuel supply pressure etc - I'm sure others can add to the list.

"A bit lean" is usually a good thing as long as the emissions are actually within limits - setting it here will cause a flat spot only if you expect to floor it and get a smooth response - gentle progression of the accelerator will often avoid any noticeable flat spot because you are controlling the progression yourself rather than relying on the carb to do all the work.

What is the colour just inside the tailpipe ?

Post by **Tim Leech** » Sat Jun 04, 2011 11:41 am

Hi Brian

This was a replacement carb that I fitted (which you kindly supplied) from a 1.9 estate, I have noticed that since I swopped the carb the performance was down and quite hesitatnt unless you give it a boot full but starting much easier.

So which way do I turn it!

electrokid · Post by **electrokid** » Sat Jun 04, 2011 1:21 pm

Ah - that carb

from new it was briefly fitted to a 1.9 4x4 and set up by the owner (who's had nearly as many BXs as you Tim) so unless it's been changed since it's likely to be right since it has fuelled a 1.9 successfully but if you need to change it, adjustment to rich is usually anticlockwise - but please check around other things as well.

Tailpipe colour is a good guide to whether the carb is set correctly or not...

White - lean - CO may exceed the limit at MOT
Off white - lean - CO just below limit at MOT ****
Mid grey - neither lean nor rich - CO normally not more than 50% of MOT limit.
Dark grey - the rich end of OK - fuel consumption not brilliant
Black - rich
Black and sooty - f**cked - usually - carb usually faulty (usually fixed with a recon kit

**** this is where I'd be inclined to set it - might be harder at times to get the best from the engine but not impossible - easy enough when you get used to it's characteristics - fuel economy will be at its very best and there'll be fewer particulates in the oil over time, A lean burn runs hotter so coolant system needs to be A1.

Post by **Tim Leech** » Sat Jun 04, 2011 1:24 pm

Thanks Brian

havent looked at the tailpipe closely, just went on what the gas analyser print out states, it is WAY under the tolderances.

Will give it a 1/4 turn anticlockwise and see if that helps, all the ancillaries are good and the airfilters done about 2000 miles.

Post by **mat_fenwick** » Sat Jun 04, 2011 2:20 pm

Is this just an idle mixture screw (I would have thought so) or can you adjust the main fuelling with a screw on this carb?

Post by **Tim Leech** » Sat Jun 04, 2011 3:43 pm

Not sure to be honest mate! Anyone?

Linegeist · Post by **Linegeist** » Sat Jun 04, 2011 4:03 pm

It's idle only I'm afraid. The main jetting is controlled by just that - jets - main and emulsion.

Having said that, progression from idle is highly dependent on the idle mixture being sufficiently rich to avoid flat spots - this is what the accelerator pump's for, to 'bung a wodge' of fuel into the manifold when the butterfly snaps open.

FWIW, my new Weber's flat as a pancake from takeoff if I set the idle mixture to lean(ish ... 13:1) but if I set it rich (10:1) it's perfect, and fuel economy's unaffected ... because the fuelling under load's controlled by the main jet.

Post by **Tim Leech** » Sat Jun 04, 2011 4:07 pm

Ahh ok, never mind, I will give the idle a slight tweak and put some bigger boots on

, it COULD be that ive been driving the TZi auto quite a bit (what a great car) which you only have to dab the throttle and its away. So could be down to pilot error not giving it enough throttle!

citsncycles · Post by **citsncycles** » Sat Jun 04, 2011 8:37 pm

Carb settings usually remain correct - if it seems it needs adjusting it's usually something else that's going wrong and adjusting the carb is lilkely to be covering up a problem that's developing elsewhere.

And

This was a replacement carb that I fitted (which you kindly supplied) from a 1.9 estate, I have noticed that since I swopped the carb the performance was down and quite hesitatnt unless you give it a boot full but starting much easier.

There aren't any air leaks on the manifold joints are there? I don't know if BX's are prone to this, but the Solex carbs fitted on 2CV's are prone to their mating faces bowing slightly, and if they aren't swapped together with their insulating block they can suck air in, which would give you the lean readings you are getting. Squirt some WD40 over the joint with the engine running and see if the engine speed changes.

Post by **Tim Leech** » Sat Jun 04, 2011 9:05 pm

Worth a try thanks!

Post by **Tim Leech** » Tue Jun 07, 2011 9:37 am

Well she did 320 miles on Sunday to Wells Next the Sea with East Midlands CCC group and never missed a beat and used just over 3/4 of fuel and alot of that was stop start town driving.

It seems I was not pressing the throttle hard enough as when I opened her up on the A47 she didnt hang about

Front spheres seem to be a bit passed there best though as it did crash over the bumps a bit more than I would expect.

citronut · Post by **citronut** » Tue Jun 07, 2011 1:09 pm

the idle adjuster screw is at the throtle cam and has a spring under its head,

the fuel mix (mixture ) screw is in the base of the carb, inside a hole at the rear N/S corrner and adjusted with a small screw driver, going in with its handle pointing at the O/S rear of the battery,

it is still anticlockwise to richen it up when faceing it,

regards malcolm

Post by **Tim Leech** » Tue Jun 07, 2011 1:15 pm

citronut wrote:the idle adjuster screw is at the throtle cam and has a spring under its head,

the fuel mix (mixture ) screw is in the base of the carb, inside a hole at the rear N/S corrner and adjusted with a small screw driver, going in with its handle pointing at the O/S rear of the battery,

it is still anticlockwise to richen it up when faceing it,

regards malcolm

Thanks Malcolm

Ive decided to leave well alone as it runs so well I dont want to spoil it!

Tim

maxgreenwood · Post by **maxgreenwood** » Thu Jun 16, 2011 9:17 pm

this is all very interesting stuff, all this info is exactly what i need to experiment towards the smooth running of my new motor. It's not that bad really, perfectly drivable, but getting the power delivery and suspension right is really important to me for some reason. I want it smooth and smooth that's my only criteria!