Mk3 Cavalier Owners Club | Vauxhall Cavalier Dot Com

My 2.0i CD 8 valve passed the MOT but only just on mixture. It has always been very economical returning 40+ to the gallon. Recently this had dipped below that figure which was confirmed by the emisions result!
The Haynes manual refers to setting the mixture (no cat) by adjusting the tamper proof screw in the air mass meter - removing the tamper plug to gain access - but it doesnt say which way to rotate it for richer or leaner?
I know I could just turn and see what happens but I would like to start turning in the right direction - does anyone know which way is what?

Alan

Woa, it's been a long time since I did one, but I think it is clockwise to lean it. You'll soon see as the meter will change a few seconds after you turn it.

Thanks, it gives me a good starting direction! Do you know if there is much adjustment available?
I ask because my Gunson tester is not that responsive and I think I might have to go to my Friendly MOT man and it would be nice to know if there is a 'pot' in there or a 'multi turn type pot' and start with a quarter turn or 2 turns?

Alan

alanw wrote:Thanks, it gives me a good starting direction! Do you know if there is much adjustment available?
I ask because my Gunson tester is not that responsive and I think I might have to go to my Friendly MOT man and it would be nice to know if there is a 'pot' in there or a 'multi turn type pot' and start with a quarter turn or 2 turns?

Alan

No, it's slow to respond mate, quarter turn does nothing, more like two turns to get a decent response. Just make sure you count the turns if in doubt, you can always put it back to where it was then. Just make sure it's a non cat 20ne, because if it has a cat the pot won't do anything.

Cheers!

Update on the mixture screw.
I prised out the anti tamper plug to find a large (10mm) brass slotted screw - gave it 2 turns clockwise with my Gunson up the exhaust, and it made it richer!
I finally settled on 1 turn anticlock - which definately leaned it off, but the Gunson is not very good at these low figures so I will have to see how it goes.

Alan

I said it had been a while, lol

Well, just returned from a long weekend in the New Forest covering some 430 miles of mixed roads and am pleased to report the consumption has returned to its old self, returning 43 mpg overall.
I am not convinced this is totally down to me having a go at the mixture screw but think I may have had some poor petrol as well.
Anyway, the Cav is running a treat and a pleasure to drive, great car, highly recommended!

Alan