More handy tuning tips for modular carburetors: Part 2

More handy tuning tips for modular carburetors: Part 2

  Part 2 of 2: By Sam Logan. Download hi-res images and text here. If you ever have the chance to discuss engine tuning troubles with the legendary Jon Kaase, you’ll rejoice in his simple logic. “Most engine troubles,” declares Kaase, “are centered on spark or fuel—if it has the former it is either getting too much or too little of the latter.” In the first part of this series of Handy Tuning Tips, we asserted for the benefit of the young enthusiast that the most valuable attribute of the engine is its production of vacuum.  When the vacuum is applied to the carburetor it draws a fine mixture of air and fuel through its labyrinth of tiny drillings. When the mixture is supplemented by spark and compression the engine acquires perpetual motion. But as Kaase reminds us, the air-fuel mixture must meet the correct proportions. In Handy Tuning Tips Part I, we attempted to give the potential engine tuner a command of the fundamentals. In systematic fashion we discussed the opportunities and potential problems with the idle circuit, particularly the seemingly unending troubles with poorly adjusted transfer slots. We continued with float levels, accelerator pump shooters (nozzles), and air bleeds. We concluded with an illustration of the carburetor’s base plate and identified its leading features. Here in Part II we compare the vacuum secondary-style carburetor with the mechanical secondary model, we explore the reasons for increasing the initial ignition timing, and we examine the essentials of modular carburetor’s metering block. Debunking the myth of selecting carburetor size by formula Using a formula to select carburetor size is a dubious practice....