Occasional stumble, every few months or so

[asiab3]

It's not always a situationally good idea, or even possible, but anytime a carbureted engine stumbles, you can check for fuel delivery issues by IMMEDIATELY clutching into neutral and shutting the engine off. (Coast to safety, remembering your power brakes get one or two stops before you lose the vacuum assist.) Removing the five screws and throttle return spring from the top plate of the carburetor will allow you to peek down inside the float bowl and see if you have a fuel starvation issue. (Careful with the gasket!)

An ignition switch issue could be ruled out with a (fused) wire from battery to coil #15/+ on long drives, though it's a pain to have to shut the engine off from the engine compartment. Sometimes you can catch a geriatric switch by gently stirring the key around at idle after a long drive and listening for a misfire or downright stall. Sometimes.

I have never heard the battery/Pertronix theory. Does that shop sell batteries on commission? Running above idle, any alternator will put out about 14-volts, which is what the electrical system will run at, allowing for a few volts of drop along the 28 feet of wire to the coil from the alternator. Considering the Pertronix installation manuals list their operating voltage as 8-16 volts, there's no way a battery could still start a VW bus AND cause low voltage problems at speed with a HEALTHY Pertronix module.

Healthy? What's that? I've got wheel bearings to grease…
Robbie

[JLT]

I have never heard the battery/Pertronix theory. Does that shop sell batteries on commission? Running above idle, any alternator will put out about 14-volts, which is what the electrical system will run at, allowing for a few volts of drop along the 28 feet of wire to the coil from the alternator. Considering the Pertronix installation manuals list their operating voltage as 8-16 volts, there's no way a battery could still start a VW bus AND cause low voltage problems at speed with a HEALTHY Pertronix module.
Robbie

That makes sense to me. The key word, as you say, is "healthy." Some stuff I've read elsewhere mentioned that this is a recent problem with Pertronix, so there might have been some glitch in their manufacturing process. When I mentioned that my Pertronix unit was eight years old, the Kombi Haus boys figured that the ignition wasn't the problem.

I'll keep y'all posted, and hope to see you at the RendezVW.

[asiab3]

Ha! I didn't want to include too much anecdotal evidence, but of the five bad Pertronix modules I witnessed last year, four of them were less than a year old… One was at Maupin!

See you there :)
Robbie

[JLT]

Ha! I didn't want to include too much anecdotal evidence, but of the five bad Pertronix modules I witnessed last year, four of them were less than a year old… One was at Maupin!

Interesting.

Another lesson that can be learned from my experience last weekend is how capricious fate is. When you think it's a trivial problem, it often turns out to be a major one. On the other hand, when you think it's a major problem, it turns out to be a trivial one.

This is how VWs instruct us in the ways of life.

[Amskeptic]

I have never heard the battery/Pertronix theory. Does that shop sell batteries on commission? Running above idle, any alternator will put out about 14-volts, which is what the electrical system will run at, allowing for a few volts of drop along the 28 feet of wire to the coil from the alternator. Considering the Pertronix installation manuals list their operating voltage as 8-16 volts, there's no way a battery could still start a VW bus AND cause low voltage problems at speed with a HEALTHY Pertronix module.
Robbie

I mean REALLY now, pshaw.
Colin

[asiab3]

Are you agreeing or is there a hole in my logic that I'm not seeing?
Robbie

[Amskeptic]

Are you agreeing or is there a hole in my logic that I'm not seeing?
Robbie

That is over-the-top agreement. I mean, what kind of crazy "explanation" do people have to come up with
"They said that the Pertronix ignition, which I got with my Aircooled.net SVDA distributor, likes to have a fully charged battery, and that low-battery situations can sometimes mimic a fuel-starvation situation."

Did they miss the alternator or generator output when you are in the "fuel starvation scenario"??
So yeah, someone is trying to sell batteries or something ...
Colin

[JLT]

And it's BAAAAAAAAACK!
That's a lie. It never really left.
I don't do much driving these days, but the few times I've had it out for long day trips or overnights, this happens:
1. After an hour or so on the road, engine stumble and lugs.
2. I pull off the road, shut the engine off.
3. I go back to the engine compartment and check for any loose wiring in plugs, dizzy, and coil. I usually don't find any.
4. I get back into the car, start it up, and then drive the rest of the way with no problems. I've "faith healed it."

It occurs to me that this never happened to me until I got the Pertronix ignition. So I'm now thinking of taking that dizzy out and putting in my old 009, and see if that makes a difference. My other recourse is to find a SVDA distributor, or convert the present distributor back to points (if that's possible) and see if I get any difference. The third recourse, of course, is to get a DVDA distributor (with points) and see how that works with the Brosol carb I have. The fourth recourse is to get a DVDA distributor and a 34 PICT 3 carb, but I gather that I need some other doohickeys which may or may not be in the bus if I really want to make that work.
Advice?

[Amskeptic]

Good god, the detours we like to take ... Hey John, since this thread began, I have logged 110,000 miles of air-cooled Volkswagen all over the place. I had a sharp intermittent stumble problem develop on NaranjaWesty in early April as I drive across the country to catch the eclipse. I overthought it all over the place, but I was scientific and made sure to note *what it was not*. Eventually, I found the problem:
There is a plastic plug that fits in the little square window in the distributor where the primary wire goes through to the points and outside to the condensor. The plastic had cracked. No more stumble.
Colin

[JLT]

Good god, the detours we like to take ... Hey John, since this thread began, I have logged 110,000 miles of air-cooled Volkswagen all over the place. I had a sharp intermittent stumble problem develop on NaranjaWesty in early April as I drive across the country to catch the eclipse. I overthought it all over the place, but I was scientific and made sure to note *what it was not*. Eventually, I found the problem:
There is a plastic plug that fits in the little square window in the distributor where the primary wire goes through to the points and outside to the condensor. The plastic had cracked. No more stumble.
Colin

I'll take a look.
Interestingly, my other option was to swap the dizzy out for the 009 I keep as a backup. That would have "solved the problem" without really diagnosing it.

[JLT]

There is a plastic plug that fits in the little square window in the distributor where the primary wire goes through to the points and outside to the condensor. The plastic had cracked. No more stumble.
Colin

That plastic plug doesn't exist in the Pertronix distributors that AirCooled sells. Instead, I saw a black plastic grommet through which the two wired from the ignition were routed (the ones that go to the coil). The grommet looked in pretty good shape to me, but if the stumble continues, I'll replace it with sealant.

[Amskeptic]

There is a plastic plug that fits in the little square window in the distributor where the primary wire goes through to the points and outside to the condensor. The plastic had cracked. No more stumble.
Colin

That plastic plug doesn't exist in the Pertronix distributors that AirCooled sells. Instead, I saw a black plastic grommet through which the two wired from the ignition were routed (the ones that go to the coil). The grommet looked in pretty good shape to me, but if the stumble continues, I'll replace it with sealant.

We don't blame it until it tells us.
Colin

[JLT]

Well, here's an update of sorts:

I haven't been doing much traveling this summer, because I had to do the driving for my wife while she was sorting out some vision problems (now cured, thank God). But the few times I took the bus out for extended drives, I got the stumble again, most recently last weekend. As usual, "faith healing" did the job, but this is getting old.

So yesterday, I pulled the SVDA distributor and put in the old 009 that I had as a backup. (Yes, I plugged the vacuum port on the carb. Not my first rodeo.) I'll run that for a while. If I get the stumble again, I'll be putting money on the Brosol carb, or at least taking it apart to weigh the float like Daniel did. Otherwise, I'm back to square one.