non standard exhaust effecting mixture
Posted: Fri Mar 23, 2012 8:56 am
My 2200 princess just failed emmisions on it's MOT - it was running OK I thought 
CO was 11% and well over the 4.5% limit, the makers spec being 2.5% +/- 1%. I ran a check with a gunson gastester and it confirmed the testers result, very rich mixture at idle
Ok I have now re-set the carbs and it's OK but the question is - why should it go so far out? Last years figure, about 3k miles ago, was well
below 2.5%.
The only thing done to the car engine wise, apart from an oil and filter change, was fitting a new custom made stainless exhaust last summer.
The exhaust was designed for quietness rather than a sporty sound and as the car ran very well I didn't consider any attention to the tuning was necessary.(carbs are SU HIF) The engine runs with electronic ignition so similarly I didn't think timing checks necessary.
Any experience out there of exhaust systems effecting mixture strength
Or indeed mixture strength richening up for any reason - like unusual needle or jet wear
Looking back over three MOT results, the annual mileages are similar and the CO and HC have remained low untill this one so whats happened
CO was 11% and well over the 4.5% limit, the makers spec being 2.5% +/- 1%. I ran a check with a gunson gastester and it confirmed the testers result, very rich mixture at idle
Ok I have now re-set the carbs and it's OK but the question is - why should it go so far out? Last years figure, about 3k miles ago, was well
below 2.5%.
The only thing done to the car engine wise, apart from an oil and filter change, was fitting a new custom made stainless exhaust last summer.
The exhaust was designed for quietness rather than a sporty sound and as the car ran very well I didn't consider any attention to the tuning was necessary.(carbs are SU HIF) The engine runs with electronic ignition so similarly I didn't think timing checks necessary.
Any experience out there of exhaust systems effecting mixture strength
Or indeed mixture strength richening up for any reason - like unusual needle or jet wear Looking back over three MOT results, the annual mileages are similar and the CO and HC have remained low untill this one so whats happened