Re: Evinrude Ficht 150 . . . WOT => low RPM's
http://www.bassandwalleyeboats.com/output.cfm?id=942823 <br /><br />Tach Trouble<br />Here's what to do when you can't read the revs.<br />John Tiger Jr.<br />Bass and Walleye Boats<br />April 1, 2003<br /> Email this article to a friend!<br />No single instrument is more important to a performance-minded boater than the tachometer. It is the most relied-upon instrument on the dashboard, and the one you glance at most often. It tells us if the engine is running up to par, if the props still all there, and if the setup is working to its maximum potential. All the more trouble, then, if your tach suddenly stops working.<br /><br />Unfortunately, this is a fairly common occurrence. But, since a tachometer is fairly easy to troubleshoot, finding and fixing the problem shouldnt be too difficult for most savvy backyard techs. Tach trouble usually takes one of three forms: Either the unit stops working altogether, its deemed inaccurate, or the setting switch (if so equipped) is out of adjustment. If yours has a switch on the back, be sure its set (usually on the 12 position, corresponding to the 12-pole alternator used on most large outboards) to match your engine.<br /><br />Of the three types of problems, total failure is most common. Unless its way off, a misreading tach can easily go undetected. Cross-checking it against another tach thats known to be accurate is the only way you can be sure that yours is telling the truth.<br /><br />BUY THE BOOK<br /><br />Before attempting to troubleshoot your tachometer (especially electrical circuits), get your hands on the factory service manual for your make and model of outboard. Most manuals will walk you through a simple procedure for checking the tach circuit. At least for Mercury, Johnson and Evinrude outboards, the tachometer circuit wire is light gray. It typically starts at the engines rectifier and/or stator assembly, is routed through the wiring harness, and then to the key switch or control box at the helm. From there it leads to the back of the tachometer. Most tachs use four wires: switched power on (usually purple); ground (black); light circuit (blue); and signal input (light gray).<br /><br />It is easiest to check for 12-volt power and proper ground first. A volt-ohmmeter or 12-volt test light are great tools for this procedure. Simply ground the meter or light, turn the key on and touch the positive probe to the purple wire on the back of the tach. You should see 12 volts indicated on the meter, or if youre using a test light, its bulb should illuminate. Reverse the leads to check for proper ground, or use the ground wire on the tach to ground your meter or test light.<br /><br />If either the power circuit or ground is the culprit, you can repair the problem and the tach should work fine. In a no-power situation, see if your tach has an inline fuse. These often blow due to constant vibration. After inspecting for power and ground, if it still doesnt work, its time to check the signal-input source, or the tach itself.<br /><br />CALL IN A BACKUP<br /><br />A simple way to determine if the tach is bad is to use another tach. I have an Evinrude digital tachometer thats fitted with clip-on alligator leads for just this purpose. Its a quick job to duck under the dash, clip the leads to the existing tach, and start the engine to see if the shop tach works. If it does, the boats tach is no good.<br /><br />In the event you dont have access to a shop tach, youll have to refer to the manual to check the signal source. The signal is a pulse-positive output thats provided directly from the alternator (stator) assembly through the rectifier. A peak-reading voltmeter set to positive and the lowest volt scale will enable you to read any voltage output (on this circuit) from the stator.<br /><br />Check the procedure and specifications for your engine, since the inspection point, procedure and wiring are not the same for all outboards. In addition, your ohmmeter can be used to check the continuity of the stator windings, as well as the integrity of the rectifier diodes.<br /><br />Oftentimes, the voltage regulator and rectifier are a combined assembly containing an imbedded tach circuit. When one component fails, they may all fail resulting in an inoperative tach, as well as the loss of battery charging. This happened last season on my 1993 Evinrude 225; not only did I lose the tach circuit, by using an in-line ammeter I determined that the battery was not being charged. Replacing the stator and regulator/rectifier assembly (a combined $500 in parts) fixed both problems. Check carefully, and bring it to your dealer if youre unsure of your findings. Most dealers wont take returns on electrical parts, so be sure your purchase is justified before whipping out the wallet.<br /><br />TRUST YOUR EYES<br /><br />In many cases, you can detect a failure by closely examining the parts. In particular, check the plastic coating of the stators wire windings. If it appears melted or burned, its almost a sure bet that the stator needs replacing. This may require removing the flywheel, however, so you can really see the part to examine it.<br /><br />Fortunately, testing it is much easier. The leads are readily accessible on most engines, and it is simply a matter of hooking up the ohmmeter and following the manuals procedures. In some cases, the rectifier and stator test OK, but the tach still doesnt work. In this case, check the continuity of the gray wire and every connection on its way to the tach. Assuming this checks out, youre back to using a shop tach to verify if the boats tach is on the fritz.<br /><br />DIALING IT IN<br /><br />Dont be surprised if your tachometer is a bit off compared to an accurate shop tach. Some are inaccurate by as much as 500 rpm. If yours reads within 100 rpm of the shop tach, its pretty close.<br /><br />Many units have a small adjustment screw on the back that can be used to increase accuracy. With the engine running and the shop tach hooked up, compare the readings and then adjust the boats to match. In my experience, digital units are inherently more accurate. Evinrudes (847/689-7090; evin rude.com) and Johnsons (847/689-7090; johnsonoutboards.com) quartz digital tachs are among the most accurate Ive seen, as are the Gaffrig units by Livorsi Marine (847/548-5900; livorsi.com).<br /><br />Dont get caught in the trap of trying to adjust a tach at lower ranges (1000 to 2500 rpm); most are reasonably accurate in the lower end of the scale. Its at the upper end (5500-plus) that the largest inaccuracies exist. Ironically, its in this range that accuracy is most critical. Rather than trying to compare the two tachs while traveling at high speed on the lake, consider taking your rig to a service shop so a test wheel can be used to properly load your engine at higher rpm levels at the dock or in a test tank.<br /><br />Accurate tach readings are essential for high-speed setup, tuning and propping. Lacking these, its impossible to know how well your outboard is running or whether your boat is realizing its maximum performance potential.
