How to reduce co emmissions for mot

Post by **Red Westie** » 12 Sep 2008, 08:00

There are of course a whole laod of other 'initial settings' if this were new, stripped down or rebuilt.
For example; throttle stop position (where the butterfly valve comes to rest) it doesn't just cut into the venturi housing rather it rests on a stop so it doesn't cut into the venturi and stick.
Also air bypass valve (idle screw) if incorrectly adjusted can be running practically on air, screwed out to far because the CO screw is too far in and weak.
BUT.....by deduction, yours is just idling to rich...as long as things like throttle stops and throttle cables haven't been messed with propping open the venturi (butterfly) it's a simple tweak in with the small CO screw to lean off the idle mixture to below 4%
I would even ignore the manufacturers settings...not sure what ther are, something around 1-1.5% and if you do get the garage to do this then specify 3% as it will idle smoother (remember this is just the idle CO, as soon as the engine goes off idle the main fixed jet takes over and emmisions output completely changes)
Martin

Post by **Red Westie** » 12 Sep 2008, 08:00

There are of course a whole load of other 'initial settings' if this were new, stripped down or rebuilt.
For example; throttle stop position (where the butterfly valve comes to rest) it doesn't just cut into the venturi housing rather it rests on a stop so it doesn't cut into the venturi and stick.
Also air bypass valve (idle screw) if incorrectly adjusted can be running practically on air, screwed out to far because the CO screw is too far in and weak.
BUT.....by deduction, yours is just idling to rich...as long as things like throttle stops and throttle cables haven't been messed with propping open the venturi (butterfly) it's a simple tweak in with the small CO screw to lean off the idle mixture to below 4%
I would even ignore the manufacturers settings...not sure what ther are, something around 1-1.5% and if you do get the garage to do this then specify 3% as it will idle smoother (remember this is just the idle CO, as soon as the engine goes off idle the main fixed jet takes over and emmisions output completely changes)
Martin

Post by **chuckle-bus-tom** » 14 Sep 2008, 21:58

A slight tangent, but related. Took mine for the MOT end of last week at WESTSIDE MOTORS in Woodford Green, East London and they didn't even bother doing the emissions test because the van was idling so fast. I'd have thought a VW specialist, with about 6 vans on the front would know to warm a van up for at least 30 mins!

Rubbish garage. Stay clear

Post by **toshT25** » 16 Sep 2008, 01:08

Bingo, took it back for a tune, got a different mechanic, passed at 1.5%. Was a leaking gasket and needed a clean and tune + i fitted a new air filter. All cash in hand

Now it looks and drives like new (the carb) .The other mot guy wouldn't even let me take a few quick photos of the underside whilst on the ramp, said he wasn't allowed to be interrupted whilst doing the test

Chalk and cheese

btw thanks for all the advice too, appreciated and noted

Post by **ghost123uk** » 16 Sep 2008, 01:54

Glad you got it sorted

Last time I took mine I noticed on collecting it ( passed ) that I had left it running on gas !!

Actually I must dig out that MOT and see what the emissions were !

Post by **asahartz** » 16 Sep 2008, 16:16

When I took mine in for its MOT (also Solex 34 pict carb on a DG) The emissions failed because they were 0.13 over the limit

Went home, connected Gastester (not accurate but close enough to help). Turned the idle mixture screw about half a turn, reading dropped on Gastester.

Went back to MOT station and was told I'd gone too far the other way now as it was only reading 0.09!

He couldn't get a reading from the nearside tube of my twin-pipe exhaust either...

Website · Post by **CovKid** » 20 Sep 2008, 09:38

Mine just went through MOT:

C0: 0.26% (MOT limit 4.50%)
HC: 150 ppm vol (MOT limit 1200 ppm)

C0 seems incredibly low for such an old vehicle - I was quite surpised by the figure. On bugs the best you could get was just under 4.50%. Just shows the improvements with the introduction of the watercooled lump and careful tuning. Be interesting to see what figures we're all getting on MOTs.

for 1986 - 1992 vehicles the pass level is:

CO: 3.5%, HC: 1200 ppm.

For 1992 - 1994 vehicles the pass level is tougher still:

CO: 0.3%, HC: 200 ppm so I'd pass that too.

Whats the emission pass rate after that?

Post by **ghost123uk** » 26 Sep 2008, 10:27

Mine just passed it's MOT first time ( a big Phew there !! )

Emissions are =

CO limit = 3.5% - mine was = 2.16%
HC limit = 1200 - mine was = 185
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That was running on LPG at the time - not sure if that is Kosher

but hey...
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I note that some on here have posted a CO limit of 4.5% and my MOT station tested at 3.5% ??????
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Website · Post by **CovKid** » 26 Sep 2008, 12:40

Depends on the year I think. Mine is always tested at a commercial van/truck place. They're strict but always fair.