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Pull the cam cover and check the valve clearances if you think that you have a burnt valve. When I had one the symptom was serious loss of low end torque but decent top end.
 

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I played around quite a bit with timing and advance curves and I settled on 38 degrees. Retarding the ignition is unlikely to do you any good unless your engine is pinging.
 

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Something is wrong if you are out 4 turns. They should be no more than about 1.5 turns on the Webers that you have. The later emissions Webers are screwed out more. You are masking some other problem by adjusting your carbs like this. What size idle jets do you have installed? Are you confident that the float level is correct? It sounds to me like you still have an air leak.
 

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I generally agree with the above posts - to a limit. The normal idle jets for these carbs on a 2L Alfa engine are 50F8. I like to run a little lean and I prefer 50F11. But if he has these jets and he still has the problem and it is alleviated by screwing out the idle jets, then I say he has either an air leak or low float level. I don't agree that putting in bigger idle jets is the solution. It may mask the symptoms but not cure the problem. Say he has an air leak and he makes his engine run better by installing 55F8's. Then the leak gets bigger. What should he then do, install 55F9's?
 

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Next size up is 50F9 or 55F8. You have nothing to lose beyond the cost of the jets. These will make your fuel consumption worse. 19.5 mpg with SPICA cams and classic Webers is not too bad. I get 23-24 but I have emissions Webers, 10:1 pistons and big sparks which all help.
 

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Advance curves make a difference. I have posted about my experiences with the different programmable curves in the 123ignition distributor. It is easy to search and find.
 

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I always set the max advance with a strobe. There are differences of opinion about what the max advance should be. My experience is that about 38 degrees is right but some people think that it should be around 34.
 

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I use P which is TDC. I verify that the pointer is in the correct position with a DTI in the #1 plug hole. I then use a variable delay strobe. Alternatively, measure the diameter of the pulley. The circumference is pi*D. The distance from P to your new M is the circumference multiplied by max advance angle and divided by 360.
 
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