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Carb tuning [again]

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M

mgtf328

Jedi Hopeful
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I've been trying to follow the advice in the manual regarding carb tuning. I've balanced the carbs using a DIY SU Balancing Kit I made up from some bent pieces of wire and the outer tubes from a couple of writing implements (pens) which happen to fit quite neatly into the piston shafts. I've managed to get the pointers to stay together quire well through the rev range. It saves the awkward job of taking the filters off to use a Unisync.
My problem comes when I check the mixture by raising the lifting pin. The manual says to "gently push the lifting pin up 1/32" after free movement has been taken up". Because the pin is spring loaded I find it difficult to judge when the free movement has been taken up. Lifting the pin slowly it reaches a point when the engine note starts to rise a little but lifting further causes the engine to become rough tending to stall. My questions are - am I lifting too far, should I stop lifting as soon as the engine note starts to rise, why does lifting the pin further cause the engine to tend to stall? The car starts and runs well. I've managed to eliminate the tendency I had to backfire when staring from cold and, to me, the plugs seem to be a nice brown colour when I check them after stopping the engine at 2000rpm before it gets a chance to idle. However the plugs seem to get a little sooty if I check them after the car has been idling a while. Any advice would be appreciated.

Rgds

AJ
 
AJ--

You can always remove the air cleaners and lift the carb piston with your finger so you can see at what point/height the idle changes. Based on what you say regarding plug color you are probably on target. They'll get sooty at idle but so long as that burns off at revs, which it sounds like it is doing, and giving a nice tan color on the insulator consistently across the board after a hot shut-down you are good.
 
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I've experienced the same problem you have with using the lifting pin. Not only is it hard to judge 1/32" (and no more), but the front pin is difficult to access without a special tool. It's easier to judge 1/32" by lifting the piston by the damper rod barrel. Lifting the piston simulates increasing airflow through the carbs, so lifting it too much will lean out the mixture and make the engine want to die.
For me, it is much more accurate to adjust the mixtures using a Colortune. The lifting pin and Colortune are different means for the same end, but the real proof is how the engine runs and what the deposits on the plugs and tailpipes looks like. After adjusting my carbs with the Colortune, I monitor the deposits and adjust the mixtures until it produces light tan or gray deposits.
 
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