[T2] 1978 VW bus "bucking"; SOLVED ? ?

[c.dreike]

John ,

Maybe I missed it, but how did you solve the bucking problem?  Was it a 
vacuum leak?

Thanks,
Chris


On 4/8/2016 5:47 PM, John Burneskis wrote:
> Yes, I believe it was the TS II.
>
> I was able to drive from Key West to Key Largo, Florida, with some success
> after I learned the idiosyncrasy of the "bucking".
>
> I have a vacuum gauge at my glove box, reading the manifold vacuum.  I am
> able to see this vacuum as I drive.
>
> As long as the vacuum was in it's "sweet spot" all went well.
>
> The "sweet spot" was between 7 - 17 in/hg.
>
> So when I accelerated with a heavy foot, the vacuum would drop below 7
> in/hg, and the bus would "buck"..  But when I let up on the fuel pedal, so
> that the vacuum would rise above 7 in/hg, the bus would smooth out.
>
>
> Pulling out from a dead stop, it seemed like a pantomime act!  I would be
> jumping all over the place unless I was gentle on the pedal.  Getting from
> 1st to 3rd was a fun thing (not really).
>
> But wait!  What about OVER 17 in/hg?  What was the issue there?
>
> Glad you asked.  Did you notice that, while driving down the road, if you
> lift your foot off the accelerator to slow a bit, what does your vacuum
> read?  Why, 22 in/hg, {so that your decel valve opens}.  Vacuum jumps UP
> when you are slowing DOWN.
>
> And when you UP SHIFT, the vacuum jumps up to 22 in/hg IMMEDIATELY, and
> then I get "bucking".
>
> Ok, but "bucking" at the higher level only until my vacuum drops back into
> the sweet spot.  Just 2 - 3 more jumps in the sweet spot and all is smooth.
>
> So the bus runs great.  You just can't start or stop the bus, and cannot
> accelerate or up shift.
>
> Now that I think about it, my problem with stalling when coming to a stop
> light or stop sign would have been as a result of the bucking.  As I
> slowed, the vacuum would go over the 17 in/hg that was the top end of my
> sweet spot, bucking would start, and I was only able to prevent a stall by
> revving the engine in neutral to about 2200 RPM, while I was braking.
>
> Wild times.
>
> Well, I feel I have solved that problem, and now a new concern pops up: the
> alternator light.
>
> Maybe I have too much (or too little} electricity going to the alternator
> idiot light.  Or something more 'Burneskis', like, my second battery
> receives it's charge (through a relay) when the idiot light goes OUT (relay
> is activated by sharing the regulator voltage feed to the alternator
> warning light.}.
>
> Over and out.
>
> Barry sends (from Walmart parking lot WiFi in Bradenton Florida, headed to
> more beach time and Fishers Buggies on Saturday)
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