Odd idle circuit issue Edelbrock 1406

[Luva65wagon]

Hey - as I mentioned the other night at the meeting I've been trying to debug this wacky running condition on my truck. I thought it may have been the Pertronix since I has previous issues with it.

This evening after getting all the glass installed on the Ranchero I decided to look at the truck, since it needs to move to put the Ranchero where it is at. First I changed the cap/rotor/wires since a few days back I got onehelluva shock. Truck started up and ran great... for all of 30 seconds. Then in one second it started running bad again. So I decided to upgrade to the DuraSpark II setup with the GM module - since I had them. No change.

So I started turning in the idle screws to see what effect they had +/- and on the passenger side I turn the screw all the way in and the engine stalled. So I backed it out and restarted and tried the same thing on the drivers side - no change at any position. Never stalled.

So as best I can see the engine is running very lean on 4 cylinders and the idle circuit on this "new" carburetor clogged up somehow. Thing is - I replaced the carb because the truck was running like it is.

The problem did go away when I put on the new carb and I drove it about 2 or 3 months (150 miles?) and now the new carb has the same issues.

I have everything filtered, so I can't see it getting crud in it already. I does run pretty good if the choke is full out and off-idle.

Thoughts? I think I do need another test carb. Anybody?

[redfalken]

Hmmmm...this sounds similar in some ways to the problems Jeff was having. Brian and I went over yesterday and scratched our heads for a few hours. We finally diagnosed the pink resistor wire was going bad. We ran a direct 12-volt wire to the coil for a few moments and it seems his problem went away.

I'm not sure what your entire set-up is but might be something to consider. Jeff has points. He's going to get one of those ceramic ballast resistors and totally bypass the pink wire.

[Luva65wagon]

Interesting. I didn't know those pink wires failed slowly. For what it's worth, they are spliced in with a bullet connector so they can be replaced - and I have lots of them. But at the very least, you can disconnect it at that connector (inches away from the switch) and connect the solid wire there, then to the ballast resistor you add. Most of the wire is wrapped in the harness and then goes to the bulkhead connector, so the old wire sort of has to stay in. I have many harnesses I've amassed. Know it [all too] well.

As for my odd carb issue, I studied the flow schematics on-line and decided to yank the carb off this morning and pull the top off it. For a new carb there was more crud in there than I would have liked to have seen. It's got a new in-line filter and air-filter too, so scratching my head about that. The drivers side idle jet was obviously clogged by how it was behaving, though that side of the carb was cleanest. I could close off or remove the passenger side A/F adjustment screw and the truck would die. Do either thing on the drivers side A/F screw - nothing changed. That circuit was dead. It was just running the entire engine off one idle jet - which wasn't enough. With the carb off and opened I removed the idle jet assembly and looked closely at it - clean as a whistle. Blew out everything "while I was at it" and put it back together. Truck runs like a charm now.

:confused: Clearly I cleared up something that was plugged up.

So now the truck has an all-new low-budget ignition system too. Can't say it's any better than it was with the Pertronix on the small trip around the [big] block, but it is simple to repair.

So ends the saga...

Back onto the Ranchero. It must be in the carport by Saturday.

[Jeff W]

Interesting. I didn't know those pink wires failed slowly.


The Shop manual has a test to measure the voltage drop across that resistance wire. One lead on the back of the ignition switch, the other test lead on the + side of the coil, then turn the key "on".

The voltage dropped across this wire means that much less supplied to the coil to make spark.

Anything greater than 6.5 volts indicates "defective pink wire". Mine was dropping 7.5 volts. That doesn't leave much for the coil.

I drove it around today for a few miles and it's performing 90% better. I think I goofed with so many other settings, (Timing, carb) that I need to get all those dialed back to get it 100%.

If all goes as planned, I can take my time on the 200.C4 and do the swap this spring. Instead of replacing the pink resistance wire, I had Brian (he is younger, more flexible and has better eyesight) install a regular 12 volt wire from the back of the ignition switch and through the firewall and screwed a ceramic ballast type resistor in the engine compartment. This way I will have a full on 12V ignition source for the duraspark, GM module or whatever I decide to use with the conversion this spring.