MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Carbs again

Having sorted my little issue with the duff plug, I find myself tuning the carbs again - this time on 4 cylinders - ahem...

Balance seems OK, and now setting the mixture on each. Rear carb is backed off about 12 flats - as normal, lift the pin, bit of a rise but essentially no change in speed...fine.

Front carb can be backed off 18/20 flats, and yet engine speed still drops away, even when wound out so far and seemingly so rich, and defintely smokey at the exhaust. Tested with colortune, and back at 12 flats, this carb seems OK, but lift the pin and speed drops away more markedly.

Thus

Engine (now!) pulls pretty well, idles OK, both carbs set on about 12 flats back off from full in. Should I be concerned..I am getting some mixed messages here from my tinkerings...

Mark O

mark,

Did you
control the shoulder height of the jets,
centre the jets
correct or controlled the float level
controlled the function of the overflow pipes?

Flip
Flip Brühl

The carburettor adjustments have to be done with the engine warmed up - say after 20 minutes of driving. The piston only has to be lifted 1mm - many don't realise this and shove the pin up as far as it will go, which throws the results off. If you use the pin method it's best done with the air cleaners off and with a 1mm blade - a screwdriver blade the right size would do. Personally I find it better to adjust each jet a flat at a time up or down, till I get the fastest and cleanest idle - once you adjust it to the edges of weak and rich you can quickly find the best setting for each carb.
F Pollock

Fergus...thanks for that. I did not realize the pin only has to be lifted by that small amount. I will try again bearing in mind your remarks.

I too tried the other method of adjusting till I get the highest idle...Do you do this one at a time?
Mark O

don't forget those videos Mark
Nigel Atkins

Adjust the jet on one carb and then do the other. Once you've got the feel of it you'll find there will only be a 2 or 3 flat envelope between going too weak or too rich, so finding the mid point is quite easy. Make sure you reset the idle screws so they are both drawing the same amount of air (take the air cleaners off) and rev the engine a few times looking at the pistons as you do so. They should rise in unison and fall together - if one is leading the other adjust the linkage till the tipping point is identical.
F Pollock

As John Twist would say "make sure you blow it out after every adjustment".
Pete Ottewell

This thread was discussed on 18/09/2012

MG Midget and Sprite Technical index

This thread is from the archives. Join the live MG Midget and Sprite Technical BBS now