Occasional stumble, every few months or so

Carbs & F.I.

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JLT
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Re: Occasional stumble, every few months or so

Post by JLT » Wed Jun 06, 2018 11:41 am

Latest post of the previous page:

asiab3 wrote:
Fri Jun 01, 2018 10:10 pm
It will require a measuring device that you can stick the fuel pump outlet in for an exact length of time, like 20 seconds. Multiply the amount by three to get your “amount per minute” which I think the specification is listed in.
I don't have such a gauge. I also don't have a fuel line pressure tester. Maybe if Colin is at Maupin and has these things, he could loan them to me. Otherwise, I'll have to take it to Kombi Haus and spend a hundred dollars to let them do it.

Do you have a CHT gauge that would catch a fuel delivery issue like this? A spark issue won’t show up in a gauge but a lean out would show with higher temperatures leading up to the stutter and then subsiding when the fuel delivery returns to homeostasis.
No, the only temperature gauge I have is for oil temp, with the sensor that replaces the drain plug. I don't think that would be very helpful. I also have one of those laser thermometers, but I'm not sure that would be of much use here, particularly since the trouble is so transient.
-- 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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Re: Occasional stumble, every few months or so

Post by JLT » Thu Jun 21, 2018 1:28 pm

Update. I had the problem again duing the Maupin trip, always going up extended grades, in any gear from second to fourth. When it happened, I would take the load off the engine, shift to a lower gear, and slip the clutch a little to keep the revs high. That kept me going.

Unrelated to that problem, I also had an "electrical issue" when an always-hot wire to the ignition switch shorted out and burned, melting a few adjacent wires. I'm currently trying to get up the courage to start mucking with the wiring myself, but I may end up just taking it to the beamish boys at Kombi Haus and letting them deal with it.
-- 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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SlowLane
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Re: Occasional stumble, every few months or so

Post by SlowLane » Fri Jun 22, 2018 12:44 pm

JLT wrote:
Thu Jun 21, 2018 1:28 pm
Update. I had the problem again duing the Maupin trip, always going up extended grades, in any gear from second to fourth. When it happened, I would take the load off the engine, shift to a lower gear, and slip the clutch a little to keep the revs high. That kept me going.
So you have a non-stock carb (Brosol) fed by a non-stock fuel pump (ie. the hunched-over kind which you would have had to install when you installed the alternator to clear the larger diameter of the alternator). I don't mean to be pedantic, just outlining the operating parameters.

Did you replace the fuel pump pushrod with the one that is 4 mm shorter when you replaced the pump? I recall that when I installed a new pump on my '72 Super Beetle waaay back when, the pump that the VW dealer partsguy sold me was the alternator version, and then, almost as an afterthought, said "oh, yes, you will also need this shorter pushrod, but it has Porsche part number, so it will cost you $4.75 instead of the $1.50 it would have cost if it were a VW part."

Sigh. I miss the '70s.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"Wisdom comes from experience. Experience is often a result of lack of wisdom."
- Terry Pratchett

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Re: Occasional stumble, every few months or so

Post by JLT » Fri Jun 22, 2018 2:38 pm

SlowLane wrote:
Fri Jun 22, 2018 12:44 pm

So you have a non-stock carb (Brosol) fed by a non-stock fuel pump (ie. the hunched-over kind which you would have had to install when you installed the alternator to clear the larger diameter of the alternator). I don't mean to be pedantic, just outlining the operating parameters.
That about sums it up. I think that if I had to replace the carb with the Solex 34 PICT 3, I'd have to replace a bunch of other stuff that came with it but which I no longer have (if indeed I ever did, because the bus may not have had the right carb when I bought it ... the distributor was definitely not the right one). OTOH, the Brosol had been running well for the past seven years, until this stumbling thing started happening.
Did you replace the fuel pump pushrod with the one that is 4 mm shorter when you replaced the pump?
Yup.

sgkent has been in touch with me about several other things that might be wrong with the fuel system, and I'm eliminating them one by one but still haven't nailed down the problem. I will definitely let y'all know what happens down the road.
-- 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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Re: Occasional stumble, every few months or so

Post by SlowLane » Fri Jun 22, 2018 4:33 pm

JLT wrote:
Fri Jun 22, 2018 2:38 pm
SlowLane wrote:
Fri Jun 22, 2018 12:44 pm

So you have a non-stock carb (Brosol) fed by a non-stock fuel pump (ie. the hunched-over kind which you would have had to install when you installed the alternator to clear the larger diameter of the alternator). I don't mean to be pedantic, just outlining the operating parameters.
That about sums it up. I think that if I had to replace the carb with the Solex 34 PICT 3, I'd have to replace a bunch of other stuff that came with it but which I no longer have (if indeed I ever did, because the bus may not have had the right carb when I bought it ... the distributor was definitely not the right one). OTOH, the Brosol had been running well for the past seven years, until this stumbling thing started happening.
Did you replace the fuel pump pushrod with the one that is 4 mm shorter when you replaced the pump?
Yup.

sgkent has been in touch with me about several other things that might be wrong with the fuel system, and I'm eliminating them one by one but still haven't nailed down the problem. I will definitely let y'all know what happens down the road.
Okay, i'm just going to throw in a possibility here, and that is that your alternator-friendly fuel pump may not have the requisite capacity to keep your float bowl full when the engine is at full load and sucking fuel for all it's worth.

That fuel pump was fitted to alternator-equipped Beetles from 1974 onwards, but the bus (in the US and Canada anyways) never had that combination, because it had been upgraded to the Type IV powerplant in 1972. So the hunched-over pump may have only been spec'd to be adequate for powering the lighter, more fuel-efficient Beetle, Ghia and Thing.

Just a thought.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"Wisdom comes from experience. Experience is often a result of lack of wisdom."
- Terry Pratchett

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Re: Occasional stumble, every few months or so

Post by wcfvw69 » Fri Jun 22, 2018 6:59 pm

I'd wonder how much the fuel pump push rod is sticking up above the fuel pump stand at it's highest point? It should be 13mm. A lot of these cheap, third world fuel pumps are notorious for putting out 5+ PSI. As a result, some folks shove too many gaskets under the fuel pump. They do this to move the fuel pump up and away from the push rod to reduce the stroke. This in turn reduces the fuel pressure. It also can reduce the volume of fuel to where an engine can suffer fuel starvation under a load.

I think more likely is the fuel pump is getting weak and is not producing enough volume under load. I ran a very thirsty 2277 engine in my bug. It had a cheap, alternator style pump. It had no problem keeping up with the fuel demands of the dual Weber 44's. Not that I ever drove that engine hard :)

Stick a fuel pressure gauge between the fuel pump and carb and see what that pumps pressure is.
1970 Westfalia bus. Stock 1776 dual port type 1 engine. Restored German Solex 34-3. Restored 205Q distributor, restored to factory appearance engine.

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Re: Occasional stumble, every few months or so

Post by Amskeptic » Fri Jun 22, 2018 8:18 pm

I had a chance to look at it at Maupin! I wudda, cudda, shudda.
Colin
(enjoying your book regardless . . . I am just where you all shut down the touristy hang-gliding school and you got a job with a hang glider manufacturer and you rebuilt your engine because you wanted to, this time)
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 84,400 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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JLT
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Re: Occasional stumble, every few months or so

Post by JLT » Sat Jun 23, 2018 1:12 pm

SlowLane wrote:
Fri Jun 22, 2018 4:33 pm

Okay, i'm just going to throw in a possibility here, and that is that your alternator-friendly fuel pump may not have the requisite capacity to keep your float bowl full when the engine is at full load and sucking fuel for all it's worth.

Just a thought.
My thought as well. The alternator and fuel pump were installed by Ronnie Feitelson's garage in Lake Havasu City, and I would have assumed that he would be savvy enough to know if there were any adaptation problems. But maybe not.

I will have that checked out sometime soon.
-- 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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Re: Occasional stumble, every few months or so

Post by JLT » Sat Jun 23, 2018 1:17 pm

Amskeptic wrote:
Fri Jun 22, 2018 8:18 pm
I had a chance to look at it at Maupin! I wudda, cudda, shudda.
Well, I didn't feel that had a right to your time, since there were people there who were paying you good money for that. And I figured that you had a right not to be hit up for free advice every time you show up at a gathering. Was I wrong about that?
(enjoying your book regardless . . . I am just where you all shut down the touristy hang-gliding school and you got a job with a hang glider manufacturer and you rebuilt your engine because you wanted to, this time)
Well, to be honest, the last time I did something to an engine when I didn't absolutely have to was a few years ago when I took out George's engine for the first time. (That comes later in the book.) Before that, my buses were daily drivers and I had to get them back on the road immediately.
-- 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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Re: Occasional stumble, every few months or so

Post by Amskeptic » Sat Jun 23, 2018 8:57 pm

JLT wrote:
Sat Jun 23, 2018 1:17 pm
Amskeptic wrote:
Fri Jun 22, 2018 8:18 pm
I had a chance to look at it at Maupin! I wudda, cudda, shudda.
Well, I didn't feel that had a right to your time, since there were people there who were paying you good money for that.
There were? They did?
Colin :cyclopsani:
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 84,400 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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