Section : Carburettors

Running rich 

Posted By : Ben Ferguson, 28-Feb-2004, 08:44pm

Hi all, just a simple (I hope!) question, does running slightly too rich affect performance at all? Mine, I just found out was running too weak, after putting air filters over the ram pipes it now does 95mph instead of 85 and a 0-60 in 12.5 secs...not bad for just adding an extractor exhaust and 1.5" SU's
The reason I ask is because I was reading "Retro Cars" mag and it has an article about Triumphs on a rolling road, with the testers commenting that most of the cars were running too rich, but not explaining why this was a bad thing, apart from wasting petrol of course.

Thanks, Ben

• Running rich 

  Posted By : Nigel Gibbins, 01-Mar-2004, 11:36am

  Ben,
  
  As we all know getting the mixture right for each of our cars requires a fine balance. If you're tuning for power then the mixture is ususally biased ever so slightly rich and if you are tuning for economy then it's biases ever so slightly weak.
  
  We all know that a weak mixture can cause overheating and eventually destroy your engine, but running rich can also have a similar effect.
  
  Richer fuel mix burns quicker and so the timing is affected and so detnation is more prevelant and that can destroy your engine. But before that happens the rich fuel mix can cause premature wear of the bores as the unburnt/extra gases can 'wash' the bores out and cause excessive wear.
  
  NiG
  http://www.niginthecar.net

  • Running rich 

    Posted By : Tim Everitt, 03-Mar-2004, 01:00pm

    Running a LITTLE rich probably won't do much harm, and if you've set up twin SU's in accordance with Triumph's recommendations, it will be a little rich. You might have a problem around MOT time though, I know I did.
    
    Tim.

    • Running rich 

      Posted By : Ben Ferguson, 03-Mar-2004, 01:27pm

      Hi,
      Thought thats what might be the case. I think i need different needles as mine seems to run rich at tickover then get weaker at the top of the rev range. I have ram pipes on the carbs which up until recently I ran without filters, but after deciding this wasn't such a good idea put home made 1/2 inch thick sponge filters over them (until I summon up the money to buy real socks!) This had an amazing affect on performance, boosting top speed by 8-10 mph! These filters however make it run even richer at tickover it would seem.
      Can anyone suggest any suitable needles for twin 1.5's (On a 1300 standard cam)? Its currently running AAT's I think...but AAQrings a bell 2!
      
      Thanks again,
      Ben

    • Running rich 

      Posted By : James Carruthers, 03-Mar-2004, 03:22pm

      Ahhhh yes...
      
      Knowing my old Spit would probably fail on emissions I decided to lean it off a bit...
      
      So I drove to the MOT station - opened the bonnet - turned the mixture nuts a set number flats lean...
      
      The car limped in to the MOT station - and it passed with flying colours - it then limped out... and I turned them the same number of flats rich...
      
      
      
      James
      
      69 Signal Red Spit
      

      • Running rich 

        Posted By : Jason Chinn, 04-Mar-2004, 08:42am

        That would be as bad as one set of tyres going round three friends and appearing at the same MOT station - testers only comment "These alloy wheels are popular, this is the third Mini I've seen with them on this month" - ahh the stupidity of youth - I hasten to add I did not have a Mini, I was the odd one out - I had a Vitesse

        • Running rich 

          Posted By : Graham Reeks, 04-Mar-2004, 08:47am

          What age do cars have to be to get emissions tested. No MOT tester's ever been anywhere near my GT with an emissions testing device ... and if they tried i think i'd have to beat them away with a wheel brace

    • Running rich 

      Posted By : William Davies, 03-Mar-2004, 09:19pm

      Emissions on a Herald should never be a problem at MOT time unless your engine is about to die. If there is a problem, find a garage who understands the emissions testing regualtions for pre 1975 (I think) vehicles. Whatever the cutoff date, all Heralds should only be tested for "Excessive visible smoke",
      Cheers,
      Bill.