My 20hp Merc (serial number 7054275) had a no-spark problem. I diagnosed the problem as a bad switch box.<br /><br />I got the switchbox installed (Merc part) and the motor fired up on me, but there is still a problem. Now when the motor starts it revs really fast right away. The throttle seems to make no difference in engine speed. The only way I can slow the engine down is to choke it with the choke. If I use full choke, it stalls. But if I can get the choke just a little less than full it will run close to idle speed, albeit very rough and with lots of smoke. Also, the throttle seems to be effective again if the choke is on. As soon as I push the choke off, it revs up really fast, but seems to smooth out. <br /> <br />What would cause this to happen? I went over my wire connections and I looks like I have everything in the right place. Any advice anyone can offer is appreciated.
