Rough idle at standstill

[Justin71]

I'm gonna throw one out here that is unlikely, but a easy thing to check/fix... Points and condenser (or more precisely "strength of spark". Points can get "burned" and condensers CAN actually go bad. Heres my recent experience:

Our 71 which was running great, but started having strange problems slowly. Problems came on in one week and then slowly got worse into the next, ending with the car just flat dying in the driveway on a trip home from church.

When it was running rough at first, it was mainly at idle and generally when the car was cold - if I get it moving, it seemed to be better. We usually drive it on short trips (~5mi). then the car seemed to "act cold" for an entire trip. rough idle, sometimes sputtering. Right before it "gave up the ghost", it was running very rough, and would just die (seemingly immediately) during idle.

I did usual checks. Thinking fuel pump and filter - exonerated those by just removing fuel line and making sure fuel was getting pumped by cranking it. Sure enough plenty of fuel. checked filter, blew it out in reverse, seemed fine. I then put fuel lines back in place, and tried cranking while spraying engine starter in carb. NO FIRE. Aha. Even with fuel it was not firing (no spark), or not firing at right time (bad timing).

Next I went after spark. I pulled #1 plug and laid the bare spark plug wire connection next to block. Very few and very weak sparks. So, it's ignition side. Next I looked at coil. I replaced it and improved electrical connections to it, still, not regular spark, and plug wire had to be very close to block (1/16th pf an inch to get it to produce any arc).

I popped the distributor and looked inside. Points very clean, look new. But, problem has to be somewhere ignition side. I grabbed a 20 yr old condenser (literally 20 yrs old!) and threw it in, and POW! massive sparks from wire next to block and engine runs smoothly (obviously missing on #1 with wire off).

Bottom line - it was the condenser! First time ever for me. But give it a try. It's a $10 part! Mine gave me some flaky behavior that wasn't obvious what was going on during it's failure.

Good luck!

Jay

 

[JimNiki]

Make sure you leads aren't arcing when they're not supposed to.

Run it in complete darkness and look for arcing.

 

[woodsnake]

Any idea how old the timing gear set is? A worn timing gear/sloppy chain will cause all kinds of intermittent issues just like this. One way to check the wear in the chain, is while you have the timing light pointed at the balancer, quick snap the throttle. If the timing marks come right back and steady, you chain is in good condition. If the timing marks "slide" up and down, then that indicates that it is sloppy, and should be replaced.