Occasional stumble, every few months or so

Carbs & F.I.

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asiab3
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Re: Occasional stumble, every few months or so

Post by asiab3 » Sun May 19, 2019 3:15 pm

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
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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JLT
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Re: Occasional stumble, every few months or so

Post by JLT » Sun May 19, 2019 3:54 pm

asiab3 wrote:
Sun May 19, 2019 3:15 pm
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.
-- JLT
Sacramento CA

Present bus: '71 Dormobile Westie "George"
(sometimes towing a '65 Allstate single-wheel trailer)
Former buses: '61 17-window Deluxe "Pink Bus"
'70 Frankenwestie "Blunder Bus"
'71 Frankenwestie "Thunder Bus"

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asiab3
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Re: Occasional stumble, every few months or so

Post by asiab3 » Sun May 19, 2019 7:34 pm

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
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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JLT
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Re: Occasional stumble, every few months or so

Post by JLT » Mon May 20, 2019 12:41 pm

asiab3 wrote:
Sun May 19, 2019 7:34 pm
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.
-- JLT
Sacramento CA

Present bus: '71 Dormobile Westie "George"
(sometimes towing a '65 Allstate single-wheel trailer)
Former buses: '61 17-window Deluxe "Pink Bus"
'70 Frankenwestie "Blunder Bus"
'71 Frankenwestie "Thunder Bus"

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Amskeptic
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Re: Occasional stumble, every few months or so

Post by Amskeptic » Fri May 24, 2019 7:26 am

asiab3 wrote:
Sun May 19, 2019 3:15 pm
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
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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asiab3
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Re: Occasional stumble, every few months or so

Post by asiab3 » Fri May 24, 2019 11:41 am

Are you agreeing or is there a hole in my logic that I'm not seeing?
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Amskeptic
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Re: Occasional stumble, every few months or so

Post by Amskeptic » Fri May 24, 2019 8:06 pm

asiab3 wrote:
Fri May 24, 2019 11:41 am
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
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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