Suddenly Won’t Idle below 1800 rpm???

[Don Frelier]

Did you maybe get the firing order incorrect?

I did have something similar happen once, the bushing on the distributor shaft was too dry and started binding up.
The car would start and run fine above a certain RPM but wouldn't idle.
But this would be a very very rare thing.

 

[dvw]

It ran fine before wiring repair. Then still ran,but though a little ruff. Then after the pick up coil was replaced it really wouldn't idle. There is your answer.
Doug

 

[Geoff 2]

I do not see how high idle rpm could be a p/up problem. If the p/up contacts the reluctor [ no gap ], you get no spark. Similarly, if the gap is too big, you get no spark. If the gap is borderline [ getting too big ], you might get spark on some cyls, not on others.

 

[artr8]

Have you considered a cross up of either pickup or coil wires? Since burned wiring, may have swapped polarity.

 

[Don Frelier]

Have you considered a cross up of either pickup or coil wires? Since burned wiring, may have swapped polarity.

I had the same thought

 

[dodtorcito]

For me, or idle air bleeds clogged or timming moved during some operation (perhaps dist.weights or vac advance). Check with the timing light.

 

[Geoff 2]

Maybe the acc pump passage has a leak, inside the carb. If the gasket leaks, fuel gets pulled into the vacuum cavity for the p/valve. That goes straight into the engine! Later Holley carbs had a brass transfer tube with o rings to stop the leak, but I think this mod was done after the 6 pack carbs were made.

 

[mmissile]

Usually been air-bleeds in the past. This last time, it was sealer [silicone?], under the carb adapter plates on my sheet-metal crossram... that had broken down and was a vacuum leak. Took it all apart and made proper gaskets. It's now running perfectly.

 

[PurpleBeeper]

UPDATE - just got back from working on the car.
1. Swapped back to previous cap/rotor and it “seemed” to be slightly better. (?) It seems to want to idle about 1200-1300 rpm after the engine is warmed up…not 900 rpm like before the repair, but not 1800 rpm anymore.
2. Checked very closely for any vacuum leak, but all hoses in that part of the motor look OK. I’m not running vacuum advance & the nipple off the center carb is plugged (just like before repair). As mentioned, I already replaced the front vacuum secondary hose which had definitely gotten torched. No signs of a vacuum leak.
3. While starting the engine and warming the engine up, I did have one “cough” out of the center carb, but as mentioned before, I’ve previously installed the little “check ball” in the center carb base plate to prevent blowing out power valves.
4. I did have some blow-by looking smoke coming out of the larger (5/8”) hose at the back of the air cleaner….but then it went away.
5. Also, I moved the rotor back & doth to make sure the timing advance wasn’t jammed…seems OK.
6. I still need to put a timing light on it, but as mentioned, I never moved the distributor, just replaced the pickup on the motor.

My next guess is that somehow I’ve gotten a spark plug wire (likely passenger side) that has slipped back off of one of the spark plugs giving me an “on again/off again” loose connection one one of the cylinders. I’ve had this problem several times before over the years. I also might have burned up a spark plug wire (since I had a fire near the distributor) & maybe I just haven’t found the burnt wire yet. Several plug wires have soot on them, so that seems possible too. The headers were too hot to shove my arm down there to check for a loose plug wire at the spark plugs….so that’ll be the first thing I check next time

 

[LowBikeMike]

It doesn't matter if you didn't remove the distributor, the new pickup might index differently causing your timing to be way off. Doublecheck timing.