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thewum
Samba Member
Joined: January 10, 2006
Posts: 12
Location: Bournemouth, UK
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 Posted: Tue Jan 10, 2006 2:59 pm Post subject: Blocked Central Idling System |
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Hi there
I have a problem with my central idling system. When the engine is cold, it runs too fast and when it warms up it stalls at junctions.
I have narrowed the problem to the central idling system. When I initially hold my finger over the air intake of the central idling system, there is limited suction. If I hold my finger on there for a few seconds and release it, it seems to unblock it. It soons blocks again however.
Does anyone know a good way of cleaning this more permanently??
I have a 2.0 air cooled twin carb.
Thanks very much
Dave |
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Amskeptic
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Joined: October 18, 2002
Posts: 8586
Location: All Across The Country
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| Posted: Tue Jan 10, 2006 3:11 pm Post subject: Re: Blocked Central Idling System |
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| thewum wrote: |
I have a problem with my central idling system. When the engine is cold, it runs too fast and when it warms up it stalls at junctions.
I have narrowed the problem to the central idling system. When I initially hold my finger over the air intake of the central idling system, there is limited suction. If I hold my finger on there for a few seconds and release it, it seems to unblock it. It soons blocks again however.
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When the engine is on the chokes, the vacuum retard does not function, the central idling circuit is not really in the picture.
With a warm engine, if you find that you can rescusitate the central idling circuit's hiss by briefly blocking the tube, that is likely to be a partially sticking cut-off solenoid plunger.
You need to:
A) make sure your vacuum retard works,
B) adjust your fast idle links
C) increase your idling air flow through the central circuit
D) lean the dual carb idle mixtures a tad
E) richen your central idling circuit mixture a tad
F) make sure you have a happy central idle cut-off, it *must* seat the plunger in the bore.
Confused yet??
Colin
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DurocShark
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Joined: April 05, 2004
Posts: 6635
Location: Crappy town in a crappy state. But the beach is nearby, so I have that going for me.
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| Posted: Tue Jan 10, 2006 3:12 pm Post subject: |
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The tubes between the carbs are clear and the hoses tight and no leaks?
BTW: Something I've been wondering about: Blocking off the central idle, and using the set screws to adjust idle. Just like more common dual carbs. I'm wondering how well that would work. Yeah, I'd lose the nice balance tube, but I'd also lose some engine compartment complexity.
Just a thought. No problems related to that on my carbs. . .
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thewum
Samba Member
Joined: January 10, 2006
Posts: 12
Location: Bournemouth, UK
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| Posted: Tue Jan 10, 2006 3:18 pm Post subject: |
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Confused? Yes!
When I put my finger over the air intake the engine idle speed increases - is this normal?
I will certainly look at all the great points you have made, but would a squirt of carb cleaner in there do any harm one evening this week until I can really get at it on the weekend??
Thank you!!  |
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Amskeptic
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Joined: October 18, 2002
Posts: 8586
Location: All Across The Country
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| Posted: Tue Jan 10, 2006 3:22 pm Post subject: |
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| DurocShark wrote: |
BTW: Something I've been wondering about: Blocking off the central idle, and using the set screws to adjust idle. Just like more common dual carbs. I'm wondering how well that would work. Yeah, I'd lose the nice balance tube, but I'd also lose some engine compartment complexity.
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That is one demerit for DurocShark.
Those stop screws are SO not to be used for idle speed adjustments.
The central circuit works *with* the dual carbs in ways you cannot. . . . in ways you cannot. . . in ways you cannot fathom. There should already be a balance tube between the manifolds, four 10mm nuts and a nice mild steel pipe.
Colin
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DurocShark
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Posts: 6635
Location: Crappy town in a crappy state. But the beach is nearby, so I have that going for me.
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| Posted: Tue Jan 10, 2006 3:33 pm Post subject: |
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What nuts????
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Amskeptic
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Joined: October 18, 2002
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| Posted: Tue Jan 10, 2006 3:46 pm Post subject: |
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| thewum wrote: |
Confused? Yes!
When I put my finger over the air intake the engine idle speed increases - is this normal?
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Nooooooo. Someone is running lean. . . .
Carb cleaner is nice for cleaning fuel deposits but may "bleach" the seat/plunger for the central idling circuit. Try it. If symptoms get worse with that potential sticking, disassemble and lubricate with a light coat of moly grease on the end of the plunger.
Colin
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Amskeptic
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Joined: October 18, 2002
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| Posted: Tue Jan 10, 2006 3:52 pm Post subject: |
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| DurocShark wrote: |
| What nuts???? |
Them nuts!
Colin
(facing the front of the vehicle, just under the carburetor bases you should have square bosses on the intake manifold castings. These bosses should have four studs, two per side. Upon these studs should be your balance pipe. The balance pipe should be attached with four 10mm nuts on these studs. The EGR pipe for us '73/74 buses used to tap into this balance pipe going from one manifold to the other.. This balance pipe is the secret to everything.
Colin
Look at "J" the red pipe. . .
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DurocShark
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Location: Crappy town in a crappy state. But the beach is nearby, so I have that going for me.
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| Posted: Tue Jan 10, 2006 3:58 pm Post subject: |
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Mine must be female... No nuts.
Just ports with hose...
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Amskeptic
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| Posted: Tue Jan 10, 2006 4:08 pm Post subject: |
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| DurocShark wrote: |
No nuts. Just ports with hose...
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When I said "facing front of vehicle" that means facing your gas tank.
I am not talking about the central idling tubes which face each other. Looking at your manifolds, I can barely discern what may be manifolds installed on the wrong side of the engine. Your brake booster taps should be on cylinders #3 and #1. If yours are on #4 and #2, then the rectangular bosses and studs and etc, will be facing the rear bumper. I can almost see the rectangular outline in your picture. You don't have the EGR valves sprouting out the sides of your manifolds, do you? You might have a late model '74 set up?
Soon, we will all be confused.
Colin
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satchmo
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Joined: November 23, 2003
Posts: 285
Location: Crosby, MN
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| Posted: Tue Jan 10, 2006 4:59 pm Post subject: |
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The worst part here is that I understand what Colin is talking about 
How about the idle enrichment device? That little rectangular thing on the side of the left carb with the electrical connection. Could that be malfunctioning (stuck open or closed) and cause the symptoms of which thewum speaks?
Curious.
Tim |
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Amskeptic
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Joined: October 18, 2002
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Location: All Across The Country
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| Posted: Tue Jan 10, 2006 8:03 pm Post subject: |
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| satchmo wrote: |
The worst part here is that I understand what Colin is talking about
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"We have problem on the psych ward. . . ."
| satchmo wrote: |
How about the idle enrichment device? That little rectangular thing on the side of the left carb with the electrical connection. Could that be malfunctioning (stuck open or closed) and cause the symptoms of which thewum speaks?
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Pull off the wire to your box and see what happens.
Colin
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DurocShark
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Location: Crappy town in a crappy state. But the beach is nearby, so I have that going for me.
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| Posted: Wed Jan 11, 2006 10:28 am Post subject: |
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Booster ports at 1&3 (front of bus). Diaphragms at the outsides of the manifolds.
Here are the before pics, maybe they say more?
The square ports have been jbwelded shut on these manifolds, as have the diaphragms.
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thewum
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Joined: January 10, 2006
Posts: 12
Location: Bournemouth, UK
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| Posted: Wed Jan 11, 2006 11:14 am Post subject: |
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| Where did you manage to buy your shiny new solex auto choke connectors from?? |
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DurocShark
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Joined: April 05, 2004
Posts: 6635
Location: Crappy town in a crappy state. But the beach is nearby, so I have that going for me.
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| Posted: Wed Jan 11, 2006 12:53 pm Post subject: |
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The elements?
I bought one on eBay when I first got the bus, and now I have a box full of these carbs and managed to find 2 good ones in the bunch that I cleaned up and polished.
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Amskeptic
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| Posted: Thu Jan 12, 2006 11:31 am Post subject: |
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| DurocShark wrote: |
The elements?
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Hey DurocShark, I was looking at your before picture here, look at the crosswise pipe just behind #3 spark plug that tees to the front of the engine compartment to the right of the #3 sparkplug. (there is some sort of yellow thing right under the pipe as it leaves) That is the balance pipe that connects to the front surfaces of each manifold with the now-famous 10mm nuts. Use it! Block off egr tee!
Colin
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DurocShark
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Location: Crappy town in a crappy state. But the beach is nearby, so I have that going for me.
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| Posted: Thu Jan 12, 2006 11:58 am Post subject: |
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That pipe that has a ground strap attached to it? It was never hooked up.. Just setting there. You're saying it's necessary?
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