Intermittent Spark - '73 2.0L, I've tried all the obvious things but one, apparently... Options

[CantConfirmOrDeny]

Hi all,

My son's '73 914 (drastically modified 2.3L rat motor, Weber carbs), which had been running "fine", now won't start after being parked for a week. Long story short: the spark is very intermittent - only sparks about every 3rd or 4th time that it should. It had a Crane optical pickup, so I put the points/condenser back in - same symptom! Put the Crane back in, then put a scope on the coil (-), and while cranking, I see a clean, 13.5V square pulse with a 240ms period and 180ms of dwell (Crane varies the dwell as it deems necessary, I think). If my math is right, this works out to a cranking speed of 117 RPM and a 69 deg. dwell angle, which oughta work. It always has before!

We've replaced the coil, we tried grounding the dizzy directly to the battery, we tried hotwiring the battery directly to the coil. Same symptom - only sparks every 3rd or 4th pulse. Plugs and wires are next, although why they would simply fail like this whilst parked is beyond me.

If that doesn't work, what's left? (IMG:style_emoticons/default/confused24.gif)

Cheers,
"CCoD"

[Rand]

Can't imagine the wires themselves suddenly failing, but a loose connection would sure do it. Especially the one between coil and dizzy center.

I ran into that... First occurrence it died in an intersection. Fortunately it was at WCR (Seattle) and JeffH hopped out of another teener behind me and we pushed it out of the way. It was a relief to discover it was only the middle wire coming loose. Pushed it back in and it fired back up. It acted up again later and I replaced with better plug wires for a permanent fix.