1974 Kombi misfiring

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LawrieB
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1974 Kombi misfiring

Post by LawrieB » Sat Dec 15, 2018 6:22 am

Hi all first post on forum.
I am currently based in Germany and am returning to Australia where my Kombi is located.
Was intending to use it as our run around while we are over there for 6 weeks.
Had my son take Kombi to mechanics to have host of things done in prep for this trip.
Timing
Replace cap rotor and leads.
Tune carbies.
Replace carbie couplings.
Van drove home really well (about 10km) but when started next morning ran a bit rough
with occasional back fire when engine braking.
Took it back to mechanic couldn't find any thing wrong, big mystery.
Drove to Brisbane (110km). For most of the drive it felt ok but it would back fire on
engine braking and also occasional miss/shudder when idling.
On arrival at destination engine stalled and when attempting to start there was no
indication of the starter motor clicking whiring or any thing. I am assuming that this is
a coincidental issue. Engine started easy on short jump start.
Would love some help on this one if possible. Have owned Kombi for last 15 years and
do most of the mechanicals myself but son can't help and mechanic (non vw) is no help.
Thanks in advance.

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asiab3
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Re: 1974 Kombi misfiring

Post by asiab3 » Sat Dec 15, 2018 10:23 am

Hi LawrieB, and welcome.

To get started, we’ll need to know a few things:

What tools do you have on board? A volt meter is mandatory for tracing “no crank” issues. Do you have one and know how to use it?

For now, do not assume the no-crank and backfire/toughness issues are related. The starter and intake/spark systems share very few components, so let’s treat them separately.

What kind of dual carburetors does your bus have? Did your mechanic:

a) adjust the valves?
b) set the points and timing? To what specifications?
c) check your fuel pressure? (Setting depends on carburetor model.)
d) synchronize the carburetors with an airflow tool at idle and high speed?

Please let us know all the details you can, and don’t be afraid to ask questions and clarify anything!

Welcome again, and best of luck getting your bus sorted out,
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

LawrieB
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Re: 1974 Kombi misfiring

Post by LawrieB » Sat Dec 15, 2018 11:35 am

hi Asiab3
thanks for the prompt reply.
As I said in first post I am currently in Germany so the work has been
done by a country mechanic so I'll give you what I know has been done
as reported by my son.
Tappets where adjusted and full carbie kits installed by myself prior to
leaving for Germany 6 months ago.
Mechanic was given the following tasks.
Adjust carbie balance
check and adjust timing
check and replace ignition as required.
Plus a variety of other tasks not related to the problem.
As to what he did in the way of these tasks I can't help you with
apart from as reported by my son who also owns and works on a
64 beetle that the kombi drove really well on the way back from
the mechanics and it was the next morning that the problem started.
To complicate the problem my son has now returned to Adelaide and the
Kombi is in storage until my return to Australia and what I am seeking is
some possible causes/fixes of the problem so I can attend to these in
person when I return to Australia.
I agree with you that the starting and running problems are not related
but just threw them together as they both happened at the same time.

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Amskeptic
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Re: 1974 Kombi misfiring

Post by Amskeptic » Sat Dec 15, 2018 1:41 pm

LawrieB wrote:
Sat Dec 15, 2018 11:35 am
A) kombi drove really well on the way back from the mechanics

B) it was the next morning that the problem started.

C) I am seeking some possible causes/fixes of the problem so I can attend when I return to Australia.

Lawrie, what I would do to pack up all four of my Volkswagens and just strafe the outback from Perth to Sydney every friggen summer (i.e. December-April), detour to Alice Springs!

Anyways, are these factory carburetors? I sure hope so, or all that blab below is just blab.

a) suggests that all hard adjustments are suitable

b) suggests that you address things that can change after a couple of heating and cooling cycles, i.e. see "c"

c) do the following even if you want to rationalize that you don't need to, have your son help.

1. Remove NEGATIVE terminal from battery, clean post and terminal end
2. With negative still off, do the same for the positive battery post/terminal and reinstall, not too tight.
3. With the negative still off, go to starter solenoid where you will see a 13mm nut on the end of the starter. Just check for snug-not-crazy-tight.
4. Check for cleanliness and security of ground strap between transaxle and diagonal arm bracket. I would remove both ends and clean shiny bright (or have the kid do it)
5. IF you have any question about electrical integrity up front ( an intermittent bad connection can cause idle drop-outs or an intermittent dumb dead starter) we can guide you through . . . but regardless, this step here is to trace the wires from the ignition switch to the T-8 connector and just wiggle the red/black wire, and if you see an all red wire and a black wire, follow them to destination and wiggle, that is all.
6. put negative back on battery, do not tighten stupidly.

7. Now let's address carbies. Do yours have electromagnetic cut-off jets on each carburetor, with black wires leading to them from the coil (+) 15 terminal? Read my lips, no loose connections allowed. Also, check to see if the solenoids have loosened up, just twist clockwise with your fingers. Now grab your 13mm wrench and just snug the nuts that hold the carburetors to the manifolds. It only takes a day for new gaskets to crush and allow those nuts to loosen.
These dual carb engines mostly get wonky from exceedingly dumb little things like loose wire terminals, or terminal ends shorting out against a throttle link when your son experimentally steps on the accelerator pedal all the way to the floor just once.

8. Backfires can be caused by in any of the elbows listed:
a) subtle cracks in left and right brake booster elbows or central idling air intake elbows
b) cracks in the thermostatic preheater hose that leads from the central idling distributor directly under the air filter to the valve on the right air horn (inside nipple)

9. Any reason not to check the dwell/timing? I would trust no one but myself.
I could go on all day. Report back.
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

LawrieB
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Re: 1974 Kombi misfiring

Post by LawrieB » Sun Dec 16, 2018 7:33 am

Hi Colin
thanks for the vgood advice,
Yep they are original stock carbies whole engine system pretty much stock standard
apart from points which have been replaced with electronic about 5 years back.
Re:
1: Will do
2 -4: Ditto
5: Thanks will certainly take you up on that one if theres a problem tracing wires back.
6: Will do
7: Yep have electromagnetic cut-off jets on each carburetor
Good advice on gaskets didn't think of this one.
Re loose wiring quite easy to knock a cable loose when tinkering around in
that area.
Will ask son if he did floor the pedal :profileleft: would he really do that ????
8a: My first thought as these have been on and off over the last year and had noted that
they where not as tight as I would have liked and were due for replacement in the near
future.
8b: Not sure of this hose do you know which one it is, referenced Richard Atwells page
http://www.ratwell.com/technical/VacuumHoses.html. If possible can you give me
his reference number.
9: On the list of things to do as well as pack a pair of good German overalls to take back to Oz.
Once again thanks for the help
Lawrie

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Amskeptic
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Re: 1974 Kombi misfiring

Post by Amskeptic » Sun Dec 16, 2018 8:49 am

LawrieB wrote:
Sun Dec 16, 2018 7:33 am
Will ask son if he did floor the pedal :profileleft: would he really do that ????
This is what you SHALL ask him to do while you are looking at the throttle levers/links.
Interference with choke wires is a thing!
LawrieB wrote:
Sun Dec 16, 2018 7:33 am
Not sure of this hose do you know which one it is, referenced Richard Atwells page
Lawrie
How daaaaaaaaare you. We have our own vastly superior technical library right here! Illustrated! More words than people can tolerate these days!

http://www.itinerant-air-cooled.com/vie ... =50&t=7767


Look at the two asteriks, there is the hose:

Image
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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