'67 dies when warmed up at idle

[RodA67Riv]

My '67 has developed a problem that I can't seem to solve. On cold start it fires right up and idles fine until it gets a little warmed up (2-3 mins). After that, it will die suddenly (no sputtering, no rough idle... it just stops). 

 

Assuming a fuel issue, I replace the fuel pump... Nope. Thinking that I might have an issue with a stuck float, I reset the float level, soaked the carb in cleaner, blew every orifice (jets and passageways) with an air hose, replaced the check ball and pump assembly and the internal gaskets... Nope. I checked for fuel spraying into the carb after it dies by pulling the throttle linkage. Yep, there's fuel in the bowl. Ok... Not a fuel problem.

 

On to electrical... I swapped the coil... Nope. Bypassed the coil resister wire by jumping the positive side of the coil to the battery... Nope. Cleaned the points... Nope. Still dies suddenly. No warning, no slow moaning rough idle, no gasping for life. It just dies one moment to the next.

 

Every time it dies, it will fire right back up, idle for 10-30 seconds and then suddenly die again.  If I keep it throttled up a bit, it runs ok with an occasional minor 'bog', but not enough to have to fight it with the throttle - which is why I started with looking at it as a fuel issue.

 

I haven't looked at vacuum issues since it fires and runs fine and the problem occurs suddenly without a rough idle.

 

What am I missing here? 

 

Thanks in advance.

 

Rod

ROA 15162

[63 nut]

Have you changed the condenser in the distributor I have had them go bad when warmed up and work when cold.

[JZRIV]

When it dies look in carb while working throttle to see if fuel is squirting out nozzles. Gas tank vent could be clogged. Check that there is no obstruction in vent hose.

[EmTee]

47 minutes ago, JZRIV said:

Gas tank vent could be clogged.

Try it with the gas cap off.  If it doesn't stall then look at the vent.

[RodA67Riv]

1 hour ago, JZRIV said:

When it dies look in carb while working throttle to see if fuel is squirting out nozzles. Gas tank vent could be clogged. Check that there is no obstruction in vent hose.

Thanks. I'll have a look while it's idling and see what's happening. But, if I keep it slightly throttled, it doesn't die. I've still got a float issue running around in my head despite having pulled the carb apart and seeing that the float needle and seat were already sparkling clean from the rebuild I did 6 years ago. No reason for the float level to suddenly have changed, but I went ahead and re-set it to 5/16" as it was about 1/32" off.  

 

I blew an air hose thru the fuel and return lines when I had the pump off. I was thinking that perhaps the pickup sleeve in the tank might be clogged, but light pressure from the air hose resulted in gurgling in the tank - while also confirming that I have gas and my gauge hasn't suddenly gone bonkers ;). 

Edited September 5, 2022 by RodA67Riv
typo (see edit history)

[RodA67Riv]

3 hours ago, 63 nut said:

Have you changed the condenser in the distributor I have had them go bad when warmed up and work when cold.

Thanks. I was thinking about a failing capacitor (condenser) on '3rd shift' last night while looking up the wiring diagram in the chassis manual. I'll give it a try today and let you guys know.

[RodA67Riv]

1 hour ago, EmTee said:

Try it with the gas cap off.  If it doesn't stall then look at the vent.

Thanks. I'll give it a try today. I did blow compressed air thru the fuel and return lines while the fuel pump was off just to confirm no blockage. I didn't think about the vent line off of the tank. Good call!

Edited September 5, 2022 by RodA67Riv
error (see edit history)

[RodA67Riv]

And the winner is... The condenser. Runs great now. Thanks everyone for your advice.

 

Got another question: Measuring the positive voltage at the coil, I expected to see a voltage drop after the engine is running (and warmed up), but I do not. It is a constant 12v. My understanding is that the resistance wire is by-passed when cranking to give the coil full 12v for cold starts (especially on winter days when the battery is not optimal), but once cranking stops the resistance wire drops the voltage at the coil to somewhere around 6v to help preserve the lifespan of the points. Any thoughts on why there wouldn't be a voltage drop? I don't see that the wiring harness has ever been hacked, so I don't think the wire has been replaced with a straight feed. Never seen a resistor go full closed (e.g. no resistance) when they go bad. Usually, it's the opposite (full open / no resistance). The thought here is that because there's no voltage drop that this might be causing premature points/condenser failure.

Edited September 5, 2022 by RodA67Riv
typo (see edit history)

[Jim Cannon]

Condensers fail due to age, heat and time.

 

I'm pretty sure the resistance is built into the wiring harness (but I am not a '67 expert).  With the engine running, you should read about 9 volts.

 

Did the engine ever have electronic ignition? Some of those kits want full 12 volts, so they ask you to bypass the resistance wire.

[RodA67Riv]

1 hour ago, Jim Cannon said:

Condensers fail due to age, heat and time.

 

I'm pretty sure the resistance is built into the wiring harness (but I am not a '67 expert).  With the engine running, you should read about 9 volts.

 

Did the engine ever have electronic ignition? Some of those kits want full 12 volts, so they ask you to bypass the resistance wire.

Hi Jim,

 

Nope, never had an electronic ignition. All original. The schematic for the '67 does show a resistance wire. I had changed the points/condenser about 6 years ago when I did the last tune up. Agree they fail. Just wondering why I might not be seeing a voltage drop, but I guess the only way to know for sure is to replace the resistance wire.

 

Thanks for your comment.

 

Regards,

Rod

Edited September 5, 2022 by RodA67Riv
typo (see edit history)

[Jim Cannon]

Honestly, Rod, I would just leave it alone. Just drive it. If the new condenser fails in a short time, start looking for causes.

 

 

[lrlforfun]

I like the gas tank. If it were electrical ...no. It's a fuel delivery problem. Blow air through the hose that goes into the fuel pump to the back of the car with the cap off. I guessin' it's the problem (restriction in the sending unit). You mentioned the choke so that's out. While you're there make sure all fuel hoses are new with fresh clamps.  Mitch

[1965rivgs]

21 hours ago, RodA67Riv said:

And the winner is... The condenser. Runs great now. Thanks everyone for your advice.

 

Got another question: Measuring the positive voltage at the coil, I expected to see a voltage drop after the engine is running (and warmed up), but I do not. It is a constant 12v. My understanding is that the resistance wire is by-passed when cranking to give the coil full 12v for cold starts (especially on winter days when the battery is not optimal), but once cranking stops the resistance wire drops the voltage at the coil to somewhere around 6v to help preserve the lifespan of the points. Any thoughts on why there wouldn't be a voltage drop? I don't see that the wiring harness has ever been hacked, so I don't think the wire has been replaced with a straight feed. Never seen a resistor go full closed (e.g. no resistance) when they go bad. Usually, it's the opposite (full open / no resistance). The thought here is that because there's no voltage drop that this might be causing premature points/condenser failure.

  Try checking voltage at the coil with the key "on" and compare to static system voltage with the key "off".... as opposed to checking voltage at the coil while the engine is running. I believe checking voltage at the coil while the engine is running is not a legitimate troubleshooting method.

  System voltage while running should be much higher than 12 volts, more like 13.5 to 14 volts depending on battery charge and system load....so if you are seeing 12 volts at the coil while running, it is, in fact, stepped down from system voltage.

  

Tom Mooney

[RodA67Riv]

3 hours ago, 1965rivgs said:

  Try checking voltage at the coil with the key "on" and compare to static system voltage with the key "off".... as opposed to checking voltage at the coil while the engine is running. I believe checking voltage at the coil while the engine is running is not a legitimate troubleshooting method.

  System voltage while running should be much higher than 12 volts, more like 13.5 to 14 volts depending on battery charge and system load....so if you are seeing 12 volts at the coil while running, it is, in fact, stepped down from system voltage.

  

Tom Mooney

Hi Tom,

 

Good to hear from you. Hope you're doing well.

 

Key on @coil: 5.42v. Key on @battery: 12.0v. Seems to be working fine. Thanks for the tip!

 

Cheers,

Rod

Edited September 6, 2022 by RodA67Riv
clarification (see edit history)