Occasional stumble, every few months or so

Carbs & F.I.

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Amskeptic
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Re: Occasional stumble, every few months or so

Post by Amskeptic » Tue Jan 07, 2025 12:03 pm

JLT wrote:
Mon Jan 06, 2025 10:32 am
Amskeptic wrote:
Mon Jan 06, 2025 5:08 am
Update?
Did we talk about fuel pump guides freezing the pushrod when the engine gets hot?
Colin
We did not. But I'll take that into account if/when the problem recurs.

It is a "thing." With engine oil, push rod should slip through a removed fuel pump spacer. Do a cross-hatch on the push rod to help hold oil. Good VW bakelite/phenolic seems to do a better job of not expanding and grabbing the pushrod enough to limit the re-stroke of the pump diaphragm. The ony indicator here is that it is a "soft" fuel failure type of lurch, not an ignition "pow-dead-oh-we're-back" sort of jolt.
Colin
BobD - 78 Bus . . . . . . . . .115,063 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles

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JLT
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Re: Occasional stumble, every few months or so

Post by JLT » Tue Jan 07, 2025 12:40 pm

Amskeptic wrote:
Tue Jan 07, 2025 12:03 pm

It is a "thing." With engine oil, push rod should slip through a removed fuel pump spacer. Do a cross-hatch on the push rod to help hold oil.
Not sure what you mean by "do a cross-hatch." Does this mean cutting grooves with a file, or using sandpaper to score the surface?

I'll be going to Buses By the Bridge, and the 600 mile road test will give me a good test of the new/old distributor-carburetor match-up. If the problem recurs, I'll do the push-rod thing and see if that helps.

Thanks for still paying attention to this.
-- 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 » Sat Jan 11, 2025 8:58 am

JLT wrote:
Tue Jan 07, 2025 12:40 pm
Amskeptic wrote:
Tue Jan 07, 2025 12:03 pm

It is a "thing." With engine oil, push rod should slip through a removed fuel pump spacer. Do a cross-hatch on the push rod to help hold oil.
Not sure what you mean by "do a cross-hatch." Does this mean cutting grooves with a file, or using sandpaper to score the surface?

I'll be going to Buses By the Bridge, and the 600 mile road test will give me a good test of the new/old distributor-carburetor match-up. If the problem recurs, I'll do the push-rod thing and see if that helps.

Thanks for still paying attention to this.

Cross-hatch as in the 220 grit sandpaper with directional sanding. Do it before you are on the road. It is a half-hour job, stick on some fresh gaskets, check pushrod protrusion and stroke as per Bentley. Is your pump German Pierburg or Brazilian? A long journey can expand the Brazilian pumps without circlips holding the pivot pin. They sometimes like to drill themselves out of the pump body and leave you stranded ... like my customer in Jacksonville Fl on his wedding day.
BobD - 78 Bus . . . . . . . . .115,063 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles

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JLT
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Location: Sacramento CA
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Re: Occasional stumble, every few months or so

Post by JLT » Tue Jan 28, 2025 2:43 pm

Amskeptic wrote:
Sat Jan 11, 2025 8:58 am
\
Cross-hatch as in the 220 grit sandpaper with directional sanding. Do it before you are on the road. It is a half-hour job, stick on some fresh gaskets, check pushrod protrusion and stroke as per Bentley. Is your pump German Pierburg or Brazilian? A long journey can expand the Brazilian pumps without circlips holding the pivot pin. They sometimes like to drill themselves out of the pump body and leave you stranded ... like my customer in Jacksonville Fl on his wedding day.
My pump is Brazilian. I took out the pushrod and found that somebody had already scored it, but I scored it some more and put it back in. I need to go over to Kombi Haus to get a new gasket. I measured the stroke at 11 mm, which is lower than the Bentley's 13 mm, but since the pump usually works just fine, I assume that the 11 mm is what it wants. There are no shims under the fuel pump pedestal, which means that I have no way of lowering it. So my money is on the pushrod is the correct one. The pump was installed by Ronnie Feitelson of Bustoration in Lake Havasu City when I converted from generator to alternator. He's done a bunch of them.

Interesting thing: the Bentley illustration shows two spring washers under the nuts holding the pump down. I saw no spring washers on my pump. So maybe I have to get a couple of those from Kombi Haus.

Lastly, I've been getting some howls when shifting gears. Justin says that it's probably the probably the throwout bearing singing its death song. That means that the engine will have to come out, so all the other crap with the clutch assembly can be inspected and replaced if necessary.

I think that this is something I'll let the boys at Kombi Haus do, since my back is giving me some trouble and I don't want to risk it further by wrestling with the engine removal. I will give them instructions to check the carb float again, since it will be real easy to get at with the engine out. (see the post at

https://www.itinerant-air-cooled.com/vi ... 15#p230507

I'll also let them change out the fuel lines, since it's been about 6 years since the last time I did it. Again, absurdly easy with the engine out.
-- 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 » Thu Feb 06, 2025 7:47 am

"since the pump usually works just fine, I assume that the 11 mm is what it wants."

"howls when shifting gears. Justin says that it's probably the probably the throwout bearing singing its death song."

Asuumptions, assumptions ...

Please answer the following:

Does it howl when you step on the clutch or when you are actually engaging a gear.

Of course the pump works fine when you don't know what that stroke specification is about.
The upstroke is actually presetting the diaphragm which discharges fuel to the carburetor on the pushrod's downstroke.
That specification is giving you your *volume*. The spring that actually pushes the diaphragm up is the pressure. I am not saying 11mm is not good enough, but you wouldn't know when it starts to lose volume under heavy demand.
Colin
BobD - 78 Bus . . . . . . . . .115,063 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles

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JLT
Old School!
Location: Sacramento CA
Status: Offline

Re: Occasional stumble, every few months or so

Post by JLT » Thu Feb 06, 2025 1:48 pm

Amskeptic wrote:
Thu Feb 06, 2025 7:47 am

Does it howl when you step on the clutch or when you are actually engaging a gear.
Yes, both things. But it goes away once the gear is fully engaged and the clutch is out.
Of course the pump works fine when you don't know what that stroke specification is about.
The upstroke is actually presetting the diaphragm which discharges fuel to the carburetor on the pushrod's downstroke.
That specification is giving you your *volume*. The spring that actually pushes the diaphragm up is the pressure. I am not saying 11mm is not good enough, but you wouldn't know when it starts to lose volume under heavy demand.
True. But that doesn't explain why it can do this going up a grade, for example, but after I do that bit of faith healing, it can resume going up that grade without a qualm, and the next one after that, and the next one after that.

I'm taking the bus out for a short spin tomorrow, and we'll see what happens.
-- 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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