'67 S ignition problem

Fidalgo911S · 08-15-2004, 01:18 PM

My '67 911S started running poorly recently - loss of power, missing, backfiring. I did a full tune-up but she still had problems. I pulled the spark plug wires one at a time at idle and discovered #1 cylinder was dead. The spark plug was new so I checked the electrical connections. I used my multi-meter to check continuity of the components. All was well. The continuity of the rotor cap was good too. Timing and dwell is spot on.

I started her up again and connected the rpm function of the multi-meter to the #1 wire. It showed zero. I swapped wires from #1 and #2 to rule the wire out and still had the same thing: the #1 wire is not getting juice to fire the spark plug. Since the rotor, points, condenser, and cap are new, I'm begining to suspect the distributor.

Before I pull it out and inspect is there anything in particular I should look for? i.e. cracks. Or have I missed something else?

john walker's workshop · 08-15-2004, 01:28 PM

see if the points are gapped properly. sometimes when the points are barely opening, bushing/shaft/lobe wear will keep the points from opening on a certain cylinder. cracks in the cap usually have a carbon track. check for some valve clearance on both rockers too. you might pull the idle jet and check for an obstruction.

Fidalgo911S · 08-15-2004, 01:46 PM

John,

I thought the same thing. Points are gapped at .016". I made sure to check the lobe at the #1 firing area.

Early_S_Man · 08-15-2004, 03:46 PM

The machining at the #1 terminal may have produced an excessive gap, and the spark may be going to ground rather than to the #1 terminal. Is this an aftermarket or genuine Bosch cap?

I suggest temporarily swapping back to the old cap, if still available, or getting another cap ... to see if the miss goes away.

If you have access to an oscilloscope, or a friend/co-worker who has one ... I suggest connecting up an inductive probe from a timing light or automotive digital multimeter to an oscilloscope ... terminated at the scope amplifier input connector with 50 Ohm feedthru termination. Clip the probe onto the distreibutor wire, and adjust the scope timebase so you will see all six pulses on screen. A missing pulse will be obvious.

Fidalgo911S · 08-15-2004, 05:50 PM

Thanks Early S, but I replaced the plug and she was firing on all six again. Why that plug failed I don't know. However, performance above 5000 rpm was still sluggish and flat.

So I rolled up my sleeves, pulled the distributor, and set about to give it a thorough cleaning. I cleaned off 30+ years of sludge and grime. It was really bad. The mechanical weights and springs were mired in old grease and dirt. It took about an hour to do the whole job. Everything was squeaky clean and shiny when I got done.

That did the trick. Now it's a whole new car. Good God does she accelerate! Thanks again for the tips.

Early_S_Man · 08-15-2004, 06:02 PM

Glad to hear that elbow grease and solvents were the heroes again!

A retrofit of a Bosch 3-pin CDI system might not be a bad idea to get rid of mid-high range sluggishness! But, the advance curve probably needs to be plotted and checked against the distributor specs.

Of course, a vat soak in Berryman's ChemDip probably wouldn't hurt the Webers a bit!

RoninLB · 08-15-2004, 11:21 PM

Quote:

Originally posted by Early_S_Man

If you have access to an oscilloscope, .

I don't know about or care about others.. but I'm gonna get one so I don't miss out on any more entertainment.

Paulporsche · 08-16-2004, 10:56 AM

Fidalgo,

Glad to hear that only a cleaning was required. BTW, I have found I can get a better read on setting my points if I forego the blade and use a dwell meter. Then I can set the dwell to the lower end of the range (wider gap) and then through wear, go past the spec and eventually wind up at the highest angle (smallest gap). In my car, that means 35 degrees to 41 degrees.