Mallory Hyfire 6a Installed, CDI works great...tach on the other hand Options

[Aaron Cox]

very smooth through the RPM range.... all with a blue coil. I have an ignitor coil to go in also......

But...as we all know...tach no workie with CDI....

and...as i read here....
914world.com writeup on how to mod a tach....

finished soldering. now for reassembly...

AA

[lapuwali]

QUOTE (maf914 @ Aug 29 2005, 08:58 AM)

QUOTE (maf914 @ Aug 27 2005, 05:19 AM) QUOTE (lapuwali @ Aug 26 2005, 01:41 PM) The later tachs don't have this problem, perhaps because they went to a shunt diode instead of just using a resistor, which will work with either the 30v spiky signal OR the 12v square wave signal.  No doubt they were responding to complaints from people trying to use aftermarket CDI boxes. James, Do you mean later 914 tachs or contemporary Porsche tachs? Would my 76 tach have the shunt diode? I'm bumping this one in the hope that someone knows about early versus late tachometers. (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif)

Sorry, didn't see this. "Early" 914 tachs (w/ silver center button) v. "late" 914 tachs (w/o silver button). The changeover was in '74 or '75. ('76 = '75, they were all made in '75, just leftover inventory).

I'm guessing on the shunt diode, btw. It seems to match what people see, but I've never pulled one apart to verify what's inside.