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 General_Failure
A.k.a.: Tristan
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 posted on April 6th, 2008 at 08:53 PM |
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Measuring manifold vacuum
Hello all.
I have been measuring the inlet manifold vacuum on my type IV 1800 van from the middle of the balance tube (where the nonworking warm air switch
vacuum connector should be). It seemed like the logical place to connect it as it provides fairly even feedback on all four cylinders.
I have two questions:
Is that a good place to connect it? Logically to me it seems perfect.
What is a standard vacuum for idling? I get about 10" Hg. or 250mm Hg. Whichever you prefer.
I have no idea what the vacuum is meant to be, but it seems a bit low to me.
If at first you don't succeed. Build, build again.
Vehicle: 1975 Special order delivery walkthrough panel based LCA pop-top camper. Motor: Nippon 1.8L Single port Wasserboxer, Transmission: 3 rib 002.
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mnsKmobi
Wolfsburg Wizard
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| posted on April 7th, 2008 at 01:10 PM |
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| Quote: | Originally
posted by General_Failure
Hello all.
I have been measuring the inlet manifold vacuum on my type IV 1800 van from the middle of the balance tube (where the nonworking warm air switch
vacuum connector should be). It seemed like the logical place to connect it as it provides fairly even feedback on all four cylinders.
I have two questions:
Is that a good place to connect it? Logically to me it seems perfect.
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Sounds like a good spot but not having a stock setup I can't be sure.
| Quote: |
What is a standard vacuum for idling? I get about 10" Hg. or 250mm Hg. Whichever you prefer.
I have no idea what the vacuum is meant to be, but it seems a bit low to me.
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Should be more like 20"
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General_Failure
A.k.a.: Tristan
Custom Title Time!
Use your head, don't abuse it!
Posts: 1036
Threads: 107
Registered: June 15th, 2004
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Location: Peaceful Finley, NSW
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Mood: Not too bad. Thanks for asking!
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| posted on April 9th, 2008 at 08:57 AM |
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That's what I thought. Weird. In all my attempts to get it running properly, the closer I got the lower the vacuum. The surging problem is
practically solved.
However... it will not start without a lot of cranking and constant accelerator pumping when the idle throat inlet tube isn't
connected. Very touchy. When it is connected it's a pretty easy start except the first start when cold.
I should say that the vacuum is relatively even. Ie. less than one gradation mark of variance between cylinders. Also compression is pretty stock on
all four.
I'm also pretty sure the issue isn't with the throttle shaft holes as this issue didn't exist after it was pulled off the road a few years ago.
One of my suspects is something along the brake booster line. I'd be happy if I could replace that horrid black plastic tube.
If at first you don't succeed. Build, build again.
Vehicle: 1975 Special order delivery walkthrough panel based LCA pop-top camper. Motor: Nippon 1.8L Single port Wasserboxer, Transmission: 3 rib 002.
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greedy53
Bishop of Volkswagenism
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| posted on April 9th, 2008 at 05:12 PM |
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i suspect the booster is leaking try it with the booster vac blocked off
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General_Failure
A.k.a.: Tristan
Custom Title Time!
Use your head, don't abuse it!
Posts: 1036
Threads: 107
Registered: June 15th, 2004
Member Is Offline
Location: Peaceful Finley, NSW
Theme: UltimaBB Streamlined2
Mood: Not too bad. Thanks for asking!
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| posted on April 10th, 2008 at 06:37 PM |
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Unfortunately I ran out of time today and didn't get to do the test on the booster, but I did start the van up and wiggle some stuff.
The right hand rubber U boot on the manifold responded to prodding on the vacuum gauge so I guess I need a new boot too. The variance wasn't massive,
maybe 1"Hg. There was also a bit off wobbliness on the throttlebar mount / autochoke etc. on the right hand side that needs investigating. However it
had no effect on vacuum.
I did this quick check while I was attacking its ancient exhaust system with muffler putty. It'll need a new one for registration, but with all the
extra whistles etc.from the leaks it made listening for vacuum leaks very difficult. It's a lot easier on the ear now.
There is one thing I noticed which I logically expected to be the case anyway, but I'll mention it here for reference.
If the manifold vacuum is being measured from the middle of the balance tube, a leak in one of the L boots will make itself known by an increased
level of oscillation in manifold vacuum.
Of course there are other factors which can cause the same thing like unbalanced carburettors or a burnt valve, but a stuffed boot is one extra thing
to check.
.
If at first you don't succeed. Build, build again.
Vehicle: 1975 Special order delivery walkthrough panel based LCA pop-top camper. Motor: Nippon 1.8L Single port Wasserboxer, Transmission: 3 rib 002.
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