How to rebuild automotive carburetors

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(not all carburetors are made with an assortment of ready made jets and air bleeds to ease an inventive tuning effort such as an experimental individual runner intake, wherefore poverty, ignorance and under-education plausibly attributed otherwise)
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The difference between the correct and too rich/lean jet sizes may only be 0.002”-0.004”. There are no readily available drill bits that are that close in size to one another. So at best, the changes made to jets by hand drilling are going to be in steps decided by the availability of drill bits. Because drill bits are often available in 1/64” increments (the small numbered bits- which have a finer increment between bits- are too small for drilling the average carb metering jet), this will be on the order of a 0.0156” change between drill bits- which is HUGE (~40%) change in metering area when in the 0.070” jet orifice range.   
 
The difference between the correct and too rich/lean jet sizes may only be 0.002”-0.004”. There are no readily available drill bits that are that close in size to one another. So at best, the changes made to jets by hand drilling are going to be in steps decided by the availability of drill bits. Because drill bits are often available in 1/64” increments (the small numbered bits- which have a finer increment between bits- are too small for drilling the average carb metering jet), this will be on the order of a 0.0156” change between drill bits- which is HUGE (~40%) change in metering area when in the 0.070” jet orifice range.   
  
It is for these reasons there is no practical way for a person to casually drill a jet and have any way of knowing what the flow is going to be. Drilling out jets is a holdover from the dark days when guys were struggling to make “high performance” engines live, and if they got within 10% of ‘right’ they were at the top of the heap. Nowadays, thankfully, we all (should) know better and leave the drilling of jets and other dubious practices to the desperate, the uneducated, and the poverty-stricken.  
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Highly educated engineers work with mathematical formulas to design correct sized orifices. During the formative years of our contemporary automotive racing environments, carburetors were not always made with a full range of ready made fuel and air bleed orifice replacements so carburetor tuning 'magic' was done with a drill. Because of the difficulty in obtaining precision, for those reasons listed above, a general recommendation to purchase an assortment of pre-calculated metering orifices (fuel or air bleeds) is emphasized. Nevertheless, carburetors exist that do not have readily available interchangeable orifices, and these warnings are made to caution the ambitious tuner.  
  
 
===Quadrajet Tuning and Repair Parts===
 
===Quadrajet Tuning and Repair Parts===

Revision as of 11:37, 7 December 2014

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