Hydrocarbons too high for mot!

[Tysoe]

Hi guys,

I need some advice. My van has just failed it's mot on the emissions test. It's Hydrocarbons are reading 1407 and the max it can be is 1200.

What is likely the cause of this?

The engine runs quite well, probably the best Aircooled engine I've had in terms of running, but it can be reluctant to start when warm. It idles well after a couple. of mins and starts fine from cold.

Any advice would be appreciated.

Thanks

[Tysoe]

Sorry also it's a 2.0 CU engine. Stock apart from electronic fuel pump.

[ZsZ]

Not know anything about petrol, but found this:
http://www.aircare.ca/repinfo-ere-causes-hc.php

[itchyfeet]

Fresh oil helps

[Dad]

Hole in exhaust.

[jason k]

weaken the mixture a smidge on both carbs, mot it and wind em back to where they were

[frankb25]

Try adjusting the volume mixture screw on both carbs as per Haynes.
Screw fully in then, 2.5 turns out.
I watched the VW guys do this years ago during the MOT and still do it before (most) MOT's.


See top picture in the following link for the screw:

http://www.ratwell.com/technical/DualCarbs.html

Hope this helps

[kevtherev]

My high HC reading was due to an air leak weakening the mixture and thus an almost undetectable misfire ..
Unburnt fuel ramping up the reading.
The O2 reading was also up suggesting that air was indeed the culprit.

[Cableguy]

Agree fresh oil does help a fair bit. Did it on my old v6 engine, passed easily having first failed on emissions

[Tysoe]

Thanks for the tips guys.

The CO reading is 0.081 and the max limit is 4.500 so i take it that's a pretty low reading and so points to no air leak. To be honest i don't know how sensitive this test is but i'm guessing that's a low reading.

I'm gonna take it for a good blast on the way to the retest tomorrow as it's not been for a good run for a while (few short slow journeys over summer and not moved much since August!). Also lower the rpm and remove the filter from the air box for the test and hope for the best.

Will reassess if it fails badly again.....

Wish me luck!

[Bigfootedboarder]

Hi
CO and hydro carbons are a little different, the CO may be less than one but and hydrocarbons are unburnt fuel emitted from the exhaust in parts per million, so you may only have 0.81% but .0.80% could be contributing to the HC's, could be an air leak as previously mentioned but that normally manifests in a poor lambda reading, it's normally Poe running, poss tight tappet, plugs etc
Being a tester myself it's worth a good run and a quick chat when you arrive to just check it on a manual test on there machine, as if it's an 'official' retest and it fails you'll be liable for a full test next time and another charge, perhaps a few cans of beer or some biscuits! That always works for me
Hope that helps

[kevtherev]

[Tysoe]

Ahhhh sound like we're getting somewhere then.

I took it for a quick drive this evening and it's not running as well as I thought. Seems to pulse when cruising at speed. Also video'd it after the drive..
https://www.youtube.com/watch?v=u1ky2SU ... ata_player

Again the idle speed seems to pulse and is close to stalling.

Have reset the volume mixture screws to 2.5 turns as suggested but it won't idle now. Would I be better off putting it back how it was? Left carb was 3.5 turns and right carb was 3.

Cheers

[frankb25]

Maybe open the scews out a 1/4 turn at a time until it will idle.
Alow 15-20 secs after each adjustment for the adjustment to take effect.
Or possibly keep the old ratio of 3.5:3 turns - ie change to 2.5 and 2 turns.
Too far will mean unburnt fuel.

Difficult without being on the analyser - a friendly MOT tester may allow adjustments during the test?
I seem to remember during one test, adjusting the right hand carb very slightly was enough to bring the HC down to <1200.

All the above assumes you have no air leaks/other problems (I should say I am no carb expert, just going on past experiences).

Hope you get it sorted.

[kevtherev]

quite right.
you need a gss analyser to set the carbs.
but first check for air leaks with some carb cleaner...otherwise any adjustment is futile