4 replies to this topic

[huw_jenks]

MG Metro, totally standard.

Hi chaps, been having some trouble getting my MG to run smoothly. I had some overheating issues during the summer and one of my short term solutions was to richen the mixture in order to make the engine run a little bit cooler, but now my cooling system is fixed I need to sort out my fuel economy.

I've been trying to get the misture back to it's normal setting using my Colortune which has always worked okay before but I've not had much luck today. I know as the mixture goes from rich to lean the colour is supposed to change from yellow through bunsen blue to a whitish blue, but no matter how much I turn the mixture screw it stays bunsen blue, the correct colour! I know the mixture is changing becuase the engine revs will increase then decrease. I also have to keep taking the airbox on and off to adjust the idle speed. So I've given up on that.

My plan now is to take it to a garage and get them to use an exhaust gas analyser to set the idle mixture, so the question is, when the mixture is at its optimum setting, what should the CO and HC levels read at idle? I don't expect most garages to know the ideal tuning for an A series engine but I'm sure someone on this forum will be able to answer my question!

Many thanks

[mike.]

Don't know anything about the readings, but if you get the car up to temp and whilst idling, lift the piston a few mil and listen to the rev's. My HIF carb has a little lifting pin to do this behind the choke, not sure if SU carbs have that. Easy enough to do manually with the air filter off though.

If they drop and engine tries to stall its too lean, if they rise and stay high its too rich. If they rise slightly and then settle back down then the mixture's right.

[petehuws]

Mike's right!! Take a look at John Twists video, really useful. For us it starts at 45seconds.



Good luck

[huw_jenks]

Thanks for the replies, very helpful but it does raise a further question. I don't have a button for lifting the piston on my HIF44 (infact, no SU carb I've ever had has had this magic button..) so I would be using the screwdriver under the piston method like in the video. But if I set the mixture like this, won't it be too rich when I screw the airfilter back in place?

And is anyone able to answer my original question?

[huw_jenks]

Bump

Any of the experts know what the CO and HC levels should ideally be when the engine is at idle speed?