tach jump

[scotty914]

lets start by saying it is more than just a mechanical thing in the tach and it is a stock 75 1.8

it jumps overa thousand rpm and stumbles when it does it and normally it does it at 4 grand if i hold it there it will go from 3500 to 45oo or so some times more
if i check the points they are set right and in spec ... if i open the dizzy and play with anything it will stop for days

i have a new cap, rotor, points and condesor
and i tore it down to the weights and cleaned it up and lubed it timing is set right but still does it after a few days

------------------
scott thacher
75 1.8 on the road again
75 under rust
(fine german rust)

[Rouser]

My experience has been that when your tach starts bouncing about as you indicate, either a wire on the distributor or coil is loose (check for tightness/crimping), the condensor is intermittant/bad, or the points (You still running points?) are bouncing about (constantly changing the gap/dwell) on a worn distributor shaft.

Unless you'd prefer to try a new set of points/condensor, the first thing I would do is eliminate the possibility and adjusting/re-adjusting/re-re-adjusting by converting to a Pertronix Ignitor unit. It has a wider tolerance (at least verses points) to loose/worn shafts, and it made my tach crisp and smooth.

If it doesn't clear up (more often it does), than the next most expensive item might be a rebuilt distributor, since you indicated that fiddling with it made it behave for a spell. Good Luck.

[John Rogers]

I would recommend using a known good test tach and drive the car to see how that one behaves. I imagine it is weak circuit inside the tach that is causing the bounce since that happened on both our 914s and getting the tach fixed by a shop was the fix. Good luck.

[24flys]

John,

How much did it cost you to get your tach fixed, mine jumps around like crazy. It's steady at idle but once I hit the gas it will jump all the way to the right. I took the instrument panel out last night and made sure all the wire were connected to the tach and it still jumps.


scott

[Dave at Pelican Parts]

Scott--check the points plate. Betcha the ground braid is a little ugly.

A points-replacement gizmo might eliminate the problem completely. I don't know if the Pertronix needs to ground through the points plate the way the points do, but the Crane does not.

The other main possibility to my mind is something in the wiring from the points to the tach--which includes the wiring from the points to the coil.

--DD

------------------
Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

[Rouser]

D_D: No, the Ignitor doesn't ground through the points plate; everything connects up outside the distributor to the coil per instructions.

Just make sure that the air gap between the trigger unit and shaft module is correct, and that the trigger unit doesn't rub up against the inside of the distributor body (for units with vacuum advance).

I've had painless installs on 009/050 and 2.0L FI distributors, and it cleared up unusual and annoying ignition hassles (bouncy tach, rough warm-up idle, intermittant miss).

[John Rogers]

I think it was approximately $75 each, but that was a couple of years ago. Good luck.

[scotty914]

well i took out the ignitor to see if it was the problem... noop
i have a second tack i could try but i have not yet i was thinking of disconnection the tach wire off of the coil to try to isolate the prob

the bearings in my dizzy are good and yes the ground braid is a little rough but the ignitor did the same thing

i will try several things tonight why cant it be a fuel problemm sense i have the fi licked and know it like my well ummm ( read as i know what it takes to squirt )

------------------
scott thacher
75 1.8 on the road again
75 under rust
(fine german rust)

[Dave at Pelican Parts]

Unplugging the tach lead from the coil should isolate the tach and its wiring from the circuit.

If that fixes your stumbling, try unplugging the signal wire from the tach (tape it up so it doesn't ground out) and plugging back into the coil. That will check the wiring to the tach.

If that is OK as well, then the problem is in your tach. I had one do the same thing. Palo Alto Speedo rebuilt it (before Pelican) for a whole bunch of money. A used one, if good, would be a much cheaper alternative.

--DD

------------------
Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

[scotty914]

well its not the tach or the wire... i unplugged the wire from the coil and it still did it ,guess i will try cutting back wires and putting new terminals on them and do a check on the wire it self

forgot to say new coil too

------------------
scott thacher
75 1.8 on the road again
75 under rust
(fine german rust)

[This message has been edited by scott thacher (edited 08-28-2001).]