tacho needle going crazy

when i first installed my speco tacho into my baja it worked great however i remember reading in the paper work that came with it that they sometimes experienced problems with old bosch ignitions found in volkswagens. they actually mentioned the make but everything was fine so i didnt worry.

i have since lost this paper work

now. about 6 months down the track its started to develop an annoying habit of flicking all over the joint. u can still sorta use it as it tends to flick up and down by about 1000 revs depending on where the needle is. usually flicks from 1000 to 2000 when idling.

engine is running fine and the same as always. what could have caused this?

is my tacho just faulty?

nick

quiet often it can just be a tiny leak of current where the terminals connect to coil, the spark or spikes in voltage causing needle to fluctuate, make sure all the terminals are tight, & the coil is very clean, step 2 is in dark preferably with blanket over open hood & your head, & engine running, see if you can see any sparks anywhere

kombikim wrote:quiet often it can just be a tiny leak of current where the terminals connect to coil, the spark or spikes in voltage causing needle to fluctuate, make sure all the terminals are tight, & the coil is very clean, step 2 is in dark preferably with blanket over open hood & your head, & engine running, see if you can see any sparks anywhere

Yep - mine was doing this last week. Also minor misfire at 5500+ rpm. Loose (+) wire on the dissy - I added a new spade terminal and now no worries all the way to 7K

I sell Speco and have installed them to a few dubs now.
Run a inline diode between the sender wire off the coil and the tacho.
Should sort it straight away.
40 cents max from any dick smith or tandy store.

replace your condenser

Could be,........
The install sheets actually suggest if you are setting them up to run with a vw engine,
You might need the diode to stop needle fluctuating.

Put a loop in the wire that attaches to the coil end or dissy end this will stop the fluctations

stop reving it "i had to say it" to compensate for my lack of knowhow

Dragbug. what you said to do with the diode, have you done that to other gauges as well? e.g. fuel and spedo that run off senders?