Hi! I don't know if this applies to your fast idle problem but I have found that several of the newer style Zama carbs have two holes in the throttle butterfly that are around 1/8 in dia. . This could and has caused a very fast Idle on some of my engines. I generally fix the problem by changing the carb. The best are the 2-needle Walbros and some of the Zamas work very well also........Bob