MOT emissions for an LPG classic

Don't know the year of it but the older DS's were just "Visible Smoke", no emmissions required.

Robin

: Don't know the year of it but the older DS's were just "Visible Smoke", no : emmissions required.

Unfortunately mine is 1975, so there are emissions regulations applicable.

Ian

My reading of the MoT Tester's Manual specifies 1st August 1975 as the date from which a probe is stuck up the exhaust.

If you are sure that the induction tract is leak-free and the air filter good, the valve openings are correct, and that the ignition timing is right (including the sate of the points, plugs, condenser, etc), then about all you have left to play with is the idle screw on the vaporiser.

I set up my open loop system pretty much as I would a carburettor, by ear, but if you find this is not good enough, then a meter is your only option. If you can't get it right like this it probably indicates a more major problem.

In theory, if you get the idle setting correct, it shoud be right throughout the rev renge. You might lose top end power if your flow valve is closed up too much.

: My reading of the MoT Tester's Manual specifies 1st August 1975 as the : date from which a probe is stuck up the exhaust.

Ah-ha. That could be useful. Unfortunately, the V5 simly says "Declared manufactured 1975", but somewhere I think I have some South African documentation confirming that she was bult in May.

Many thanks for the advice,

Ian

An HC of 2900 is massively high!!! Either you have it set to run very weak at idle and alot of the gas is failing to burn and passing down the pipe, or you have a poor burn on one or more cylinder caused by a poor spark for whatever reason.

1) Plug gaps too small. 2) HT leads / cap / arm / plugs / coil giving poor performance 3) excess oil blow by past the rings on one cylinder 4) poor compression on one or more cylinders.

Tim..

Just a thought, but it may be running too lean. With very high hydrocarbons like that it could be Hydrocarbon Inversion which can happen with gas but rarely with petrol. Did your man check petrol HC's?

Robin

: Just a thought, but it may be running too lean. With very high hydrocarbons : like that it could be Hydrocarbon Inversion which can happen with gas but : rarely with petrol. Did your man check petrol HC's?

Nope, just on gas. I'll take it round on Tuesday and have a fiddle ... maybe this means I should get round to buying that gas analyzer I've been promising myself ...

Thanks,

Ian

: An HC of 2900 is massively high!!! Either you have it set to run very weak : at idle and alot of the gas is failing to burn and passing down the pipe, or : you have a poor burn on one or more cylinder caused by a poor spark for : whatever reason.

Thanks. I'll have a good look at the plugs...

Ian

yep!

Or remember it by reg: P=pollution or K=katalyst...:-)

But 'P' isn't either Aug 74-75 or Aug 75-76......

It is in fact Aug 76-77, Doh !

Really? In which country? Here in the UK, a 'P' suffix is 75/76. In actual fact.

Doh !!! My head hurts..... :~(((

: Really? In which country? Here in the UK, a 'P' suffix is 75/76. In : actual fact.

And having checked other bits of paper, I am pretty sure the car is May 76, which is a) impossible for a DS, according to most of the books, but probably means they were assembling a few as an when needed and b) no help for the MOT. So off a-twiddling things I go ...

Ian

: So advice please ... do I : : a) twiddle things to get the HC down, then leave it like that or : twiddle it back if performance takes a hit or : : b) take it in running on petrol next time.

I decided to try it on petrol this time. HC 350ppm, sailed through.

Memo: adjust LPG setup soonest.

Thanks for all the advice,

Ian

What was the CO?

350ppm HC's is still on the high side. For an engine and carb in good order, at proper running temperature with A1 ignition, albeit a 1975 one, tuned right, I would expect 1.5%-2% CO and under 250ppm HC's.

Tim..

: > I decided to try it on petrol this time. HC 350ppm, sailed through. : : What was the CO? : : 350ppm HC's is still on the high side. For an engine and carb in good order, : at proper running temperature with A1 ignition, albeit a 1975 one, tuned : right, I would expect 1.5%-2% CO and under 250ppm HC's.

About 2.5 - 3% CO. I'll be giving it a jolly good tune up soon ... as soon as I have resolved certain technical difficulties with setting the timing. I am more concerned with getting the LPG set up right as she does most of her miles that way.

Ian

Funny - I've always worked on the principle that you got everything else right before you started messing about with carburetters or similar devices. Obviously spent the last 50 years doing it wrong. . . ;-)

Ron Robinson

: Funny - I've always worked on the principle that you got everything else : right before you started messing about with carburetters or similar devices. : Obviously spent the last 50 years doing it wrong. . . ;-)

Eh? I say "I'll sort the timing first, and then the fuel supply" and you say "sort the fuel supply after you've sorted everythig else", which is, um, the same thing, is it not?

My timing problem, by the way, comes from the fact that this is a very, very late South African DS, and a bit of a parts bin special in places. Timing on earlier D's is set by fixing flywheel position with a locating pin - this is the static firing point. On mine, the locating pin fixes TDC and you use a conventional timing scale to do the advance ... but mine was built with a DS21 BVH water pump housing, which doesn't have the timing scale. So I can easily set TDC, but accurately fixing advance is a pain ... even rigging upa pointer air't easy, as it's in the middle of a tangle of drive belts, hydraulic lines, wiring etc etc etc.

Ian

My apologies. The way I read it was that you were going to try to get the LPG right, then set the timing.

Ron Robinson