cdn914

I have a completely stock 914-6 with a persistent problem - popping from the tailpipe and missing intermittently. I have changed every ignition component including the ignition switch and distributor, and even the carburetors but the exact same problem persists. I have substituted four CDS units and the problem is exactly the same with all four. However, none of the four CD units is new. All emit a hum with the ignition on and the car does run. How would I know if the problem is the CD unit? Can they be tested and if so, how? Do they completely fail (car will not run at all), or can an intermittent problem be caused by a bad CD (or in this case four bad CD units)? Is there a better alternative to the CD ignition? Any and all suggestions very welcome.

JonM..

Sounds like you have hit all the major bases. There are a lot of aftermarket Cd's which will work for that engine if you want to try that. If you do I suggest you make a bracket such that you can mount the Cd to the original mounting points thus you won't have to drill holes in your rare car. I used a simple piece of aluminum.
I assume when you changed carbs every component was also changed jets, floats etc. Did you also change your fuel filter? Does it miss at all speeds/throttle positions? Did you balance the carbs yourself or did someone else do it? What do your spark plugs look like?
Sorry for all the futher questions, but it could make a difference.

david914

When does this "popping and missing" occur? Is it just at idle, acceleration, or cruising? It sounds to me like you may have a mixture problem. Check your plugs and see what they look like. It may be that your carbs need to be tweeked.

Steve Weiner-Rennsport Systems

cdn:

Like David, I think this might be a carburetor problem and I'd suggest the below procedures before spending anymony on ignition components.

This sounds to me like plugged idle jets and/or passages and this is very common on Webers.

I'd suggest removing all of your idle jets, draining your float bowls by removing one main jet holder from each float chmaber, and blowing the idle jet passages out several times with clean, dry air.

This is a common enough issue with Webers that many years ago, I machined a little threaded tube that screwed into the main jet passage (after it was removed) to allow pushing pressurized air back through the passage from the float bowl. This really helps remove those tiny, almost invisible particles of dirt or rust that causes an idle jet circuit to plug up and cause those very same symptoms.

The quickest way to tell if your idle circuits are not functioning properly is to drive the car and note its operation at wide-open throttle. If the popping and hesitations go away at full throttle, then you've found the problem.