MOT Emmissions

[johhny5]

Having trouble getting the emmissions right to pass the retest.
When i get the Co level below 4.5 the Hydrocarbons go up???
It should be below 4.5 % CO and 1200 hydrocarbon for the emiisons on the MOT.

Tested and dont seem to have any air leaks .

But noticed that one ot the spark plugs is a little sooty when i changed them but all the others are OK??

When the van is on idle it back fires a little may bee when your going down hill ??


Do all these things point towards something.

All i can think of is to give the carbs a clean out and double check for air leaks ,any other beter ideas and help most welcome please , please

[kevtherev]

Tested and dont seem to have any air leaks

.

When the van is on idle it back fires a little may bee when your going down hill ??

Do all these things point towards something.

and double check for air leaks ,

this the Air cooled engine?

[kevtherev]

By leaning out the mixture to get the CO down you lean it so much it fails to detonate and reads as hydrocarbons (which is what fuel is)

There is air getting into the mixture from somewhere
Have you had any compression tests done?

[johhny5]

sorry yes 2 litre Air colled CU engine on twin 34 webers,
where the hell could the air leak be ??

[kevtherev]

OK lets assume it's not a leak..
Other reasons for poor detonation, misfire, backfire and subsequent sooty plugs are.
Timing
Exhaust valve(s) burnt
wrong plug gap
poor compression

[johhny5]

ok will check it all over at the weekend but the thing with the plugs is that only one is sooty ?? and im told the CU engine has hydraulic tapets.
I assume my haynes will give me the spark plug gap

[kevtherev]

OK
one sooty plug is a good place to start... thats where the high HC is coming from
that could be a burnt valve, poor compression or poor spark.

[johhny5]

Recently fitted new rotor arm, dizzy cap, ht leads, only noticed one sooty plug when i changed the plugs.
Engine does rattle a little, it was fitted in 2004 by the previous owner.
Hasnt realy covered any great mileage.
Should i pull the rocker cover off and have little look in there, while i have the whole weekend ??

[kevtherev]

If you feel confident about it then take a look.

Take a look at the sooty plug pair of rockers... are they "spongy" or easy to rock at firing stroke TDC ?.
read the wiki regarding resetting

but do all the other stuff first.. elimination

[johhny5]

cheers thanks, will try elimination of all the easy stuff first over the weekend,
let you know how i get on

[johhny5]

Found plugs sooty on no3 and 4, left hand side of engine when viewed from the back.
Done a compression test on engine, all cylinders in the 130 lbs ball park.
Cleaned all the jets on the carbs and checked them, seem all ok.
Weekened the mixture to the offending carb until engine slowed then wound it out a little until stable at idle.
Using a hand held vac gauge tested the balance between both carbs , about the same at idle bu wildly different as you increase the revs??
Should the value on the gauge go up as you increase revs?? i asuming so but not widly differnt between carbs.
Does this point to a air leak from that side?if so where , ive tested the carbs and hoses between the inlet manifolds with wd 40 but no increase in revs so assuming leak free.
Any help greatly appreciated im in Kettering Northants or whereis my best local garage with godd knwledge of my beast please.

[weimarbus]

Is there a vacuum take off for the brake servo on the 3&4 inlet manifold, if so that vac hose will be where the air leak is. Good luck

[johhny5]

Just had a thought.
Is the left hand carb acting correctly, ie as the revs increase the little snail airflow gauge reading increases and the right hand carb is not correct?
Whilst we were away in Cornwall i had to replace the gasket between the underneath of the carb and the inlet manifold on the right hand side as it looked suspect, i am sure the vac hose between the manifolds is not leaking air this only leaves the manifold betwen the engine and the inlet mainfold or a loose manifold not sealing ??
Please some one tell me im headingin the right direction.
I plan to remove the left hand carb and inlet manifold tommorow and see what is lurking in there

Thanks for the comments so far

cheers

John

[johhny5]

bit of an update-
removed both cab and inlet manifolds from the engine
Found the sooty plugs side of the engine has no gasket between the inlet manifold and engine?????
SO i think thts my prob where the air leak is, i have ordered 2 new gaskets should be on their way to me.
I have had this van just about a year hence the MOT stuff, amazed by the previous owners bodges etc and the paperwork to show all the mechanical work was carried out in a garage???
Hope to fit the gaskets tommorow and give a quick set up just to get through the MOt emmissions
Finally happy i have found something

[johhny5]

Got 2 new gaskets from the nice people at Retrodubs in Cornwall, fitted them today, basic adjustments of carbs took it to the test station , fine tunned on the machine, then ran test.
Bobs your uncle fanny's your aunt now got nice green MOT cert
Jobs a goodn