Weird Stall While Idling but Runs Great Otherwise

[violan888]

Hello! I’m finally on the last stretches of making my beetle a reliable car. It’s a 1971 super with the 1600 dual port, 34 pict 3 carb (pretty sure it’s a Chinese remake) and my distributor is a 034 Chinese repro with electronic ignition. Originally a 070 dvda but had stumbling issues. (The 034 eliminated all of those)

Ok anyways...

The beetle runs great, drives amazing, has zero hesitation and plenty of power thanks to the new distributor. I take it a few miles down the road and hit a traffic light. It idles fine, then all the sudden drops in idle and dies all within ~2 seconds. I thought this was weird. Turned it over and the engine fired right up. I changed the cap and rotor with no change to the issue. But it fires right back up after it dies oddly enough. This never happened with the original distributor but does with the new one (yes I know it’s a Chinese make). I am unable to adjust the idle speed with it now as the idle speed screw doesn’t do anything too. I noticed that it would idle very low sometimes before dying so I thought I might adjust that. I’m just at a loss of what to do as it runs so great now but I just can’t stop and idle at a light.

Once it dies it also is making a weird air rushing noise and sparking in the cap with the key on... I made a YouTube video (with a clear cap to see the issue and sound) https://youtu.be/B_C02BXfCko the noise doesn’t stop when I unplug the coil, but does once I unplug the positive or negative wire from the coil

[old gh bug]

Chinese copies !!!!

could also have something to do with carb solenoid valve check that its working correctly

[ashman40]

I can't tell from your video but is that spark jumping from something to something? Is the spark jumping from the center post to one of the four plug wire posts?
It looks like the distributor cap post has a crack? Cracks in the plastic become paths for a spark to arc thru. Checks the cap as well as the spark plug wires. The insulation of the cap and the wires should prevent any sparks from being visible.

It looks like you have one of those cheap see-thru distributor caps? Junk it and get a proper stock distributor cap.


On you idling problem...
Since you say the problem happens after yo have driven a few miles, can I assume the choke is already OFF and the engine is warmed up? Have you tried adjusting the choke so it remains ON a few minutes longer? Maybe your engine is just not warmed up enough when the choke turns OFF?

If it is still a problem even after you engine is warmed up...
As suggested above, check the idle cut off solenoid. This solenoid allows air-fuel to flow to the idle circuit when the ignition is ON. When the ignition is turned OFF, it cuts the flow. When they fail, they cut the flow to the idle circuit and the engine struggles to idle. The bypass screw on the left side of the carb no longer has any effect because the cut off solenoid blocks the output of the bypass screw.
With the ignition ON, disconnect the wire to the solenoid on the left side of the carb and you should hear a click as the solenoid shuts OFF. Reconnect the wire and you should hear a click as the solenoid turns ON. Test this a few times. You could also unscrew the solenoid and flust out the opening it sits in to clean out any debris.

With the engine idling lower than normal, remove the air cleaner assembly and cover the carb opening with your hand to block off 75% of the air flow. Slowly move your hand to cover more and more until you hear the idle change. Ideally, as you restrict the air flow the idle will drop. But if the idle becomes stronger as you cover more of the carb opening it indicates the carb was running lean (too much air) and by cutting off the air flow you are correcting the lean condition. This typically means you have a vacuum leak (air leaking into the intake manifold). Vacuum leak can have a sucking sound if they are large enough. Check for a leak by spraying carb cleaner around all the common leak points: gaskets, hoses.
_________________
AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[violan888]

ashman40,
The spark is inside the cap. It jumps from the rotor to the contacts in the cap. It isn’t cracked or damaged and does it on all. So your first assumption is correct. Since then, I’ve changed the cap and rotor.

I believe the choke is off when this happens. I guess I haven’t really found the issue to be present when idling with the choke on. I will adjust that in a bit. The solenoid does work. It is a new carb. It does click and everything. But that is weird that it controls the bypass screw. I may tear the carb apart again and make sure it works properly.

I had a terrible vacuum leak before so it could be that I guess. I’ll start spraying fluid all around the car again! I’ll also check for lean conditions too.

[ashman40]

[Starbucket]

Since winter has arrived check to see the heat riser tube under the carb. is getting hot (start a cold motor and put your hand under the carb. area of the heat riser, it should get too hot to touch after a few min.s) if it's cold when you stop liquid gas is entering the cyl.s and stalling the motor, liquid gas only burns while vaporized gas explodes.