Tacho problem

[Ricco1]

My '82 Yamaha RS125 has developed a strange issue with the tachometer. All is fine until just under 7000 revs. So, at 50 mph 6700 rpm all is well. If I increase the revs the tacho is showing much higher revs. At 55mph it shows 8000 at 60mph 10000. The obvious thing is that the clutch is slipping but this isn't the case, I would hear this in the engine tone. It also happens in lower gears, ok to 7000, then races ahead.

The tacho is cable driven so I guess the culprit is either the drive or the tacho itself. Anyone come across this before?

[Grumpy Old Git]

Check the cable drive both ends (there should not be any swarf / burs present - remove cable drive and apply a light oil (allowing to seep into the cable)#. Check the drive from the engine casing (put a flat bladed screwdriver into the drive output and see if you can turn it (should not turn or be loose) - WARNING! Do not use force! Check the drive input to the Tacho - it should not 'wobble' and should turn freely with no 'gritty' / rough spots. If all is OK, then the Tacho is faulty - Not a simple home repair and not really worth it so... Either put up with it as is or, get a replacement Tacho.

#Remember to use the 'correct' grease when refitting the Tacho drive cable.