"bouncy" tach

[650mark]

i've read all i can find about fixing my bouncy tach and the only thing i came up with was to spray contact cleaner into the working innards of the tach while holding the unit upright so the fluid can't get to the inside of the glass.
has anybody had success doing this or do i need a new tach? finally got to put some miles on my '80 special today and found that the tach is pretty good up to about 5k rpm. as soon as i push it to about 5.5k it jumps right up to 7k, then drops down to 4k, then bounces back up to 7k. yuk! but as soon as i slow down to a steady 70mph and 5k it's fine again. btw, put 140 miles on the beast and it is a real blast to run out on the hiway. i really embarrassed a guy on a harley "chopper" going up a steep hill on the way to payson arizona. i just couldn't resist.

[bikerphil]

First, check/clean all the electrical connections coming from the alternator, the big white plug behind the fuse panel and the connections where the tach plugs in. If it still bounces after doing all of that, the problem is inside the tach unit itself. I fixed mine before by carefully opening it up (not easy). Inside I found a corroded PC board, so I cleaned all that off with contact cleaner and a toothbrush. I also saw a few flaky solder joints so I reheated them and added a small amount of new solder. I put it all back together and guess what, no more bounce! This was 5 years ago and guess what, it is starting to bounce again but nowhere nearly as bad as it did, YMMV.

[TopCatGr58]

Hey Mark,

Have you inspected all of the wires/connections from the ALT, the 3 large plugs behind the fuse block panel, as well as the connections at the gauge? Poor electrical connections can cause a whacky tach.

T.C.

[650mark]

i just installed a new stator and reg/rec unit . all plugs and connections are good. guess i'll try the spray cleaner thing next before i try to take the unit apart. a weird tach is certainly not a deal breaker, just annoying.