I have installed an Electromaxx 140amp alternator and serpentine belt kit on a 2006 Hunter 36 with a Yanmar 3YM30 having the combined VDO tacho & LCD digital hour meter type tach. Before the install the tach worked fine. After installing the alternator the tach is reading higher rpms than it should but seems to be charging normally. WOT is now reading 4800. In my research I am finding that I will have to measure the new alternator and crankshaft pulley to recalibrate the tack using a formula (crank pulley diameter/alt pulley diameter x 8). This info is said to be specific to VDO tachs. Having said that I have since calculated the pulleys and made the adjustments to the tach. What I am experiencing now is that the tach is steady at idle but reading lower than it should being around 600 rpms(I might add this is being measured by a photo tach). Then when I raise rpms the tach becomes erratic and falls to 0 rpms. Is there something I might be doing wrong? Apparently so. Is it some kind of noise interference? This kit from Electromaxx is supposed to be bolt-on and plug-in to the existing harness plug. May I add that bolt-on wasn't quite accurate as some minor fabrication had to be made for factory belt cover to fit. It would be much appreciated if there is someone with knowledge of what I am doing wrong or where to go next.
Scott
Scott
