failed mot on hc level

[3pintsNige]

Hi
My 2.0 cu engine with dellorto carbs t25 failed mot on the hydrocarbons emission levels to day.I checked for air leaks and found one, manage to fix it and took it back to the mot testers but it still failed.The van passed last year with the same set up.Does any one have any ideas what the problem could be or anyway of reducing the hydrocarbon level for the mot.
Cheers Nige

[itchyfeet]

Change the oil helps as does re routing any oil breathers away from carb(s)

[dumbo]

plus take the air filter out and let the air flow better
simon

[kevtherev]

Standard answer mate.
Compression, timing, ignition components. mixture.
High HC is usually caused by a lean mis-fire as you know.

If the HC goes down when the engine is revved it would suggest a manifold leak.

[ajsimmo]

Did your tester only check the HC at idle, or did he raise revs to 2000rpm, as he is supposed to if it fails (above 1200ppm) at idle? Do you have a printout of the actual figure recorded?

[kevtherev]

No it didn't fail Andy, HC fell over 2500 rpm

[ajsimmo]

But first post and title says failed on HC? Don't get what you mean, Kev.

[kevtherev]

HC @ idle was over 1200 ppm.
Under 1200 @ 2000 rpm
Was he wrong to fail it then?

[ajsimmo]

That should be a pass. No question.
http://www.motinfo.gov.uk/htdocs/m4s07000305.htm

[3pintsNige]

Apologise for late reply.the co reading was 2.81 and the hc reading was 3197.I took the vehicle home to have a look, found a small air leak on the carb manifold gasket and fixed it. Took it back to the mot tester, he check it again, the co was fine but hc was 7000 plus. The tester revved the engine which brought the hc level right down but the co level went over the permitted level by quite a bit. Thinking about it now he probably couldn't find the rev were both readings were below permitted levels.
Cheers Nige

[ajsimmo]

Once CO has passed at idle it doesn't matter if it increases at fast idle. If HC then passes at that fast idle it is a pass regardless of higher CO.

[kevtherev]

That seems pretty conclusive.
Thanks Andy.

[3pintsNige]

Yes cheers Andy thanks for your help.