Evening all.

I have an SJ StSt 4-1 exhaust system. Was a bugger to fit but got there in the end.

For reasons, a couple of years ago, I changed out the centre box to a through pipe - great noise.

Car now seems to run rich. Nothing else has been changed but to be honest, its always been on the richer side when my MOT garage used to check emissions or whatever.

Could the centre exhaust section be the culprit? 

I also have a K&N filter but the air intake system is otherwise stock.

Thanks in advance...

I'd be looking at the carbs and fuel pressure regular first......

I'd start by checking the carb float levels, instructions & float heights given in the manual.

Now here's a topic which takes me back to long past years, when my ride was a well tuned Elan and I travelled many a mile top down and trailing behind my good mate's S1 Esprit. That car had been fitted with a big bore 4-2-1 manifold and minimal silencer, ran like the clappers but just reeked of richness, as I complained over coffee between stints. As examination of the plugs revealed no such condition we were led to conclude that the undeniable richness of exhaust simply had to be a matter of spill through due to over scavenge during valve overlap. Neither did jetting down the Weber DCOE's to the point of surge prove to be a remedy. The car did run entirely to the owner's taste otherwise. FWIW

Thanks guys,

Float levels already checked and adjusted according to instructions because I too suspected this as a cause.

No pressure regulator on this model, although when I bought the car, someone had fitted one. Interesting perhaps.

Rejetting carbs was a thought but likely beyond my ken.

Hands up, I have not checked the plugs. Duh. I also have a colour tune that might be worth a check.

Steve, I am totally happy with how the car runs and sounds but a couple of people have commented and that has nagged at me!

I'll run those checks again and report beck.

Si

I'd add that the mate's S1 had been converted to green dot cam wheels, with 104 deg MOP thus increasing the overlap. We presume though not checked the cams to be OEM spec C type. Good thought to examine the plugs, ColourTune only useful st idle.

Cheers

If the MOT tester is using a 3 gas analyzer with the engine under load ( rolling road i.e. ) it will tell no lies as to what's coming out the tailpipe.

I have the same setup as you on my S2, Si. She's always been happier running on the richer side and plugs are nice and clean.

Pete

16 hours ago, slewthy said:

Rejetting carbs was a thought but likely beyond my ken.

You can still compare the currently fitted jets, emulsion tubes & air correctors with the ones specified in the WSM for your model. It's very possible that a DPO has  changed some of them in order to increase performance & that's what's causing the richness. The MOT measures the exhaust gas at fast idle but not under load so the idle jets would be where I'd start looking. Here's a clickable parts diagram to help.

Invaluable help everyone.

Never thought to check the jets were the correct ones to start with!

I'll hopefully get some time to do some of these checks this week.