914-6 Tach Needle Dance?

rdvnac · rdvnac's Garage

My factory 914-6 has an MSD 6AL, MSD coil, and the tach converter to make the MSD talk to my stock VDO tachometer.

This system was installed a few months ago along with new cap, rotor, points, etc., and has worked perfectly.

Lately, however, my tach needle has become extremely erratic, indicating 4k RPM then a split second later 2k RPM, etc. This is not the "bouncing" that some tachs have after a shift, it is much more instant and erratic.

Any chance this is a fuse issue or something (he asked hopefully) or do I have to turn human contorsionist/Braille reader to get to the points?

philinjax · 07-16-2002, 06:42 AM

Bob,

It's the tach converter (the problem, that is).

Phil (In DC today)

rdvnac · rdvnac's Garage

Thanks very much for the reply Phil. Have you heard of problems before with the tach converter? I would rather deal with a problem with the tach converter than points.

But, my mechanic's first guess was that the points had gotten a bit gunky from the higher intensity of the MSD system, so he recommeneded a gentle cleaning of the points and drilling a small hole in the distributor cap to vent it. As a former owner of a 964 with the infamous belt-driven dual distributors that suffered from a similar problem, this wasn't too shocking to hear....

Any thoughts, anyone??

Scott S · Scott S's Garage

Do search on the MSD/tach issue. I had the same problem. One of the listers gave me an alternate way to hook up the tach vs using the tach output on the MSD box - I cant remember if it was directly to the small white or small red wire. Once I did this everything worked perfectly.
Scott S

red-beard · red-beard's Garage

Have you really noticed much of a difference with the MSD unit vs. CD unit? This is something I have considered doing. Unfortuantely, it's hard sometimes to separate the hype from reality.

James

rdvnac · rdvnac's Garage

Thanks much for the tip Scott. I did a quick search yesterday and didn't find anything on point, but will try again tonight with this added info.

James, other folks' experiences I'm sure may be different, but I have to say that for my 914-6 the MSD set up was a small miracle. I had some popping, surging and drivability issues that were driving me (and my mechanic) nuts. The MSD stuff *eliminated* these. Now I have smooth, strong power from idle to redline. On my particular car, it was a remarkable improvement.

Hopefully, this tach issue issue is not "the other shoe dropping," because until now I have been extremely pleased with the MSD set up.

gruntie · 07-16-2002, 02:09 PM

FWIW I'm also running MSD6AL with the tach booster & whenever the tach needle starts bouncing about it has always been due to wear/deterioration of the points. If you carefully follow the procedure in the Clymer manual (ie remove the distributor) replacement is actually straightforward - but still a pain in the neck, so I'd welcome any opinion of the best optical triggering system to use with the MSD.

red-beard · red-beard's Garage

Will a Petrinox work with the MSD unit?

Ron Meier · 07-17-2002, 06:11 AM

Hey James-

Each box (MSD, Allison/Crane,?) needs a "trigger" mechanism. We used the Allison/Crane with the optical trigger in the dizzy initally, then switched to a magnetic trigger on the crank. The box worked with both.

All the trigger unit does (by light beam or mag sensor) is tell the box (capicator) when to discharge.

Give it a go - it will either work or blow the box up and with all your money - you just go buy a new one

Look at the documentation that came with your unit and see if it can be triggered by an alternate method or pick up the phone and call them.

JWest · 07-17-2002, 06:16 AM

MSDs are fairly compatible with almost any type of trigger - the best thing is to just call them and ask, though.

Bee Jay · 07-18-2002, 08:41 AM

Bob, go here:
http://forums.pelicanparts.com/showthread.php?threadid=64459
Bee Jay

rdvnac · rdvnac's Garage

Just an update and note for the archives:

Bee Jay, thanks much for digging up that link. I think in my case though, since I am using the stock points and not a Pertronix, my situation is a little different.

Also, it appears that the tach adaptor is always needed for the 914-6 engine, no way around it.

BUT, I cleaned the points (gentle rubbing with folded, crisp clean dollar bill) and drilled two 1/4" holes in opposite sides of the distributor cap. Caution: Take your time doing this with progressively larger bits--don't ask.

I reinstalled the cap and, voila, smooth running engine and a happy, steady tach. If you read the MSD materials carefully under "miscellaneous information," you will see a recommendation to drill two vent holes in "smaller caps" to prevent the air inside the cap from being electrically charged.

I am hoping this has cured my problem. So far it has appeared to do so. If not, I will post the next step. Thanks again for the help.