914 stumble/tach bounce

[JBanks]

Hello 914 experts.
My friend has a 73 2.0, with stock injection.
It drives great, but sometimes when lightly accelerating (say from 20 to 40) it develops a slight stumble. Also, every time it stumbles, the tach also jumps around erratically. The two seemed tied together. In other words, both happen simultaneously each time.
The car keeps accelerating through the stumble, and is fully driveable, its more of an annoyance than anything.
Any words of wisdom?
Thanks!

[Dave at Pelican Parts]

The problem is in the ignition circuit. The points, condensor, or wires from those to the coil. It could also be that the tach or the wires to the tach are shorting out somewhere.

Try unplugging the black-with-purple-stripe wire (looks all-black unless you look carefully) from the coil. If the problem goes away, then check that wire for broken insulation and shorts to ground, then try finding another tach.

If unplugging the tach lead doesn't fix anything, check carefully for cracked insulation on the green wire from the coil to the condensor, and the wire from the condensor to the points. Also check the ground braid inside the distributor--it is there to ground the points.

--DD

[JBanks]

Thanks Dave.
BTW, the car has some kind of ignition that eliminates the points, otherwise its stock.

[Pritchard]

I have started experiencing this phenomenon as well. Yesterday, I hooked up the timing light to see if all four cyls. were getting spark. To my surprise, when the wire from the timing light to the sensor/clip touched other parts of the engine, the timing light would pulse much more rapidly. I'm guessing I have a short somewhere. If anyone has an idea where to start looking, I would appreciate any input. BTW, I have a Pertronix Ignitor instead of points.

Thanks

David Pritchard

[Dave at Pelican Parts]

Still similar advice. Make sure the Pertronix is OK. Wires with broken insulation are bad, m'kay? (Sorry, I channeled Mister Mackie for a second there.) Make sure the pickup and magnet ring look OK, no extra scrapes or anything.

Check the wires going to and from the coil, and the tach wire. And, if you have L-jet FI, the wire from the coil into the FI.

--DD

[Pritchard]

I removed the braided ground wire in my dizzy when I installed the Pertronix. Seems like this shouldn't affect the Pertronix. Should I reinstall the ground wire, just in case?

The Pertronix seems ok. Perhaps I'll reinstall the points to verify the Pertronix. I unplugged the tach and still had the same problems.

thanks

Pritchard

[This message has been edited by Pritchard (edited 11-01-2000).]

[Dave at Pelican Parts]

I don't know where the Pertonix grounds itself. If it is through the contact breaker plate, the way the stock points are, then it needs the ground braid. If you put points back in, they will need the braid. Otherwise, it will sometimes ground and sometimes not--and you will sometimes get a spark and sometimes not.

--DD

[drew1]

Had the same stumble and tach problem in my 914 a few years ago. 009 dist with points.
Found a loose fuse caused the problem.

drew1