| Author | Message | ||
     Bitbear |
MMB Tach Needle Bounce Fix! There have been reports from time to time of Blasters with tachometer needle bounce. When I installed my Nova MMB Tach last year I had no problem; the needle was rock solid. But a few weeks ago I suddenly – sadly – started to watch my needle bounce too. I was intermittent. It would fluctuate wildly at any speed, although it would also often hold steady at constant speeds. One member said he had two MMB tachs in a row with bad bounce; he blamed the manufacturer. Another said he just lives with occasional bounce. Researching tachometer needle bounce on the Web there was a clear consensus: when electronic tachs are faulty due to a faulty circuit board they almost always fail completely, i.e., they either work or they don’t – they are seldom intermittent. Virtually all advice – for both motorcycles and cars -- is directed to reviewing the wiring for loose connections – and to consider possible RF/electro-magnetic interference induced by spark plugs and other electrical devices. Also the MMBs are German built to exacting international quality standards. So it was hard to believe that two in a row would be faulty right out of the box; too much of a coincidence. It seemed more likely to me that both tachs were affected by the same (wiring) problem on the same bike. So my effort to correct the problem started with rewiring my tach with slightly heavier 18 gauge stranded wire from the coil harness to the tach, checking and shortening all wires to remove any excess wire that might act as an antenna for RF noise, carefully checking each connection, whether it was soldered or crimped. More importantly perhaps, I wound the pulse wire with another wire, wrapping it with about one coil per inch, then grounding it at both ends. This acts as a basic electro-magnet shield attenuating any potential interference from the spark plug from interfering with the pulse signal. Much to my delight, the problem was immediately corrected – I’ve been testing for days now and it’s back to rock solid. It’s impossible for me to say whether the problem was caused by a bad/poor connection or whether it was corrected by shielding the pulse wire running to the tach. But it certain that is was one or the other. When installing your tach – or correcting needle bounce – go slow: 1) make sure every connection is absolutely solid; 2) keep all wires as short as possible; eliminate any extra wire that that could act as an antenna; 3) wrap your pulse wire with a grounded wire to shield the pulse. | ||
| Ezblast |
Merci'! | ||
| Reuel |
Radio Shack should have shielded wire that'll work, too. Conductor for signal, shield to ground. |
