Emissions

[SGN]

I checked my exhaust emissions today with an old Blue point/Snap on analyser.
It showed 12.3% & 12.1% on each exhaust:shock:
It's been a trifle smoky for a while.
So folks, where do I start?
It has new plugs,filters,cap and rotor arm and I have the Stromberg tool.
Any suggestions appreciated.

Cheers
Steve

[grahamb]

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I wouldn't take it for.a MOT until you get a more helpful suggestion

[milothedog]

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grahamb wrote:

I wouldn't take it for.a MOT until you get a more helpful suggestion

If it's a 73 car as suggested, it doesn't have to pass an emissions test other than a visual one

Ian.

[Andy Rundell]

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over 12% CO is pretty high....... before going straight for the mixture adjustment check that your plug gaps, points (unless electronic ignition) and timing are spot on. I have assumed that one of the filters you replaced was the air filter so that shouldn't be choking things up. also worth checking the breathers are all clear.

Once those things are sorted check that the choke control is shutting off, then you'll need to try mixture adjustment with the tool you mentioned you have by following guidance in the ROM. If your needles are very worn that won't be helping - but they'd need to be in really bad shape.

good luck..........Andy

[milothedog]

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SGN wrote:

I checked my exhaust emissions today with an old Blue point/Snap on analyser.
It showed 12.3% & 12.1% on each exhaust:shock:
It's been a trifle smoky for a while.
So folks, where do I start?
It has new plugs,filters,cap and rotor arm and I have the Stromberg tool.
Any suggestions appreciated.

Cheers
Steve

Mine was running very rich and the needle valve and seats leaking. when I took them off there was a large pool of fuel laying in the manifold. I used the rebuild kits from LD's (contain everything you need) the new needle valves and seats and reset floats made an amazing difference and the economy is much improved. before if I had it in the Garage running you would end up stinking of exhaust fumes, now it's fine.

Might be a good place to start and it may be why the CO reading is so high if you have all that fuel sitting there like mine had.

Ian.

Ian.

[SGN]

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Cheers for replies,
The plug gaps are ok,It's got electronic ignition.I think I need to get straight to the carbs.
Is there a base setting for the needles,something like screw them in as far as they go then back a couple of turns??

Steve

Hi Ian
You described my symptoms perfectly,just starting it to drive out of the garage fills it full of fumes.

Steve

[Andy Rundell]

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SGN wrote:

Cheers for replies,
The plug gaps are ok,It's got electronic ignition.I think I need to get straight to the carbs.
Is there a base setting for the needles,something like screw them in as far as they go then back a couple of turns??

Steve

I think it is likely that you will need to adjust the carburation - but I'd strongly recommend checking that the timing is on the money before starting on fuel - only takes a few mins.

......Andy

[milothedog]

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Hi Steve, for the sake of an hours work and £30 worth of parts why not change the needle valves and seats and see how it goes before adjusting mixtures. Like mine you may find an instant improvement and even, like mine, fuel laying in the manifold causing the high readings.

Ian.

[V Mad]

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SGN wrote:

Cheers for replies,
The plug gaps are ok,It's got electronic ignition.I think I need to get straight to the carbs.
Is there a base setting for the needles,something like screw them in as far as they go then back a couple of turns??

Steve

Check your spark plug colour; probably sooty back! Dont bother with the needles;if your emissions are that bad first check the needle valves in the float chambers and make sure you have clean fuel in there.

[Guest]

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Hiya Steve, sadly it's not as straight forward as screwing to the end of the thread, it's pretty straightforward, but you will need to take the tops off and remove the pistons, turn them upside down, wiping oil off trousers, and screw the needles until the brass needle holders are flush with the bottoms of the pistons, then raise both EXACTLY one quarter of a turn, also check for shiny marks on the needles. That's a good datum point, replace them and from there, raise or lower them to richen or weaken them to taste, as Ian says, the only MOT check is for visible smoke. Ideally the mix should be about 2 1/2 % but with wear and age you'll be very lucky, anywhere from 3 to 6 would be fine. Re-build kits are expensive, and contain loads of stuff you'll never use.If that doesn't fix it then come back and we can sort in more detail. Martin.

[SGN]

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Thanks everyone

I'll try your suggestions tomorrow,and take another reading,It's worth a try before spending,I might be lucky.

Steve

[Tdm]

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All seems a bit complex to me, but when my Stag failed its MOT on emissions I fitted a new Inlet Manifold and weakened the mixture as far as it would go using the carburretor adjustment tool. Regulations regarding emissions are stricture here than they are in the UK, but since I had a problem 3 years ago I have left the mixture weak and it has always passed its subsequent MOTs. I need full choke to start the car, but after a mile I can push the control in and it will run normally, albeit not quite as quick on acceleration as it was before but it will do me.

[V Mad]

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One of the shortcomings of the CD or variable jettype (Stromberg, SU etc) carbs is that you cannot adjust the idle mixture without changing the off-idle mixture. This is because as the needle is raised/lowered, this changes to mixture at all openings of the air valve.

When the Stromberg carb is old, the needle and needle jets may be worn unevenly and this distorts the original profile of mixture throughout the rev range. In theory, if a new original needle/jet pair are fitted, this should bring it back to the original settings, but other undetected faults within the carburettor, or in the case oftwin strombergs any imbalances between the pairmay still cause poor running.

By comparison, the fixed jet carburettors (Weber, Holley etc) haveseparate idle and main running mixture circuits, and the idle mixture can be easily adjusted by a screw adjuster.

[SGN]

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Getting there
Did all the checks, found the needles are really rough and pitted,which wouldn't clean up so I've ordered new ones, re-gapped the plugs,set the needles as Martins suggestion,and it's down to 4.2%.
I won't be able to try it on the road until the weekend,but fingers crossed it will be ok with the new needles.
Just a couple of questions:
How is the tube that holds the carb oil held in place,I have one loose.
7 Out of 8 plugs were black,except for one which was pale brown,does that mean it's not firing on that plug ?

Thanks again for everyone's help

Steve

[Guest]

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SGN wrote:

Getting there
Did all the checks, found the needles are really rough and pitted,which wouldn't clean up so I've ordered new ones, re-gapped the plugs,set the needles as Martins suggestion,and it's down to 4.2%.
I won't be able to try it on the road until the weekend,but fingers crossed it will be ok with the new needles.
Just a couple of questions:
How is the tube that holds the carb oil held in place,I have one loose.
7 Out of 8 plugs were black,except for one which was pale brown,does that mean it's not firing on that plug ?

Thanks again for everyone's help

Steve

That's an odd one, is the steel tube loose in the aluminium piston ? If so you need a new piston, it's an interference fit and not really repairable. I wouldn't worry about the plugs, it sounds as if one was trying to run correctly, check them again after about 100 miles. Sounds very promising, good luck Martin.