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Santaji
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Joined: December 29, 2007
Posts: 105
Location: Mumbai, India
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 Posted: Sun Sep 17, 2017 8:19 am Post subject: FI Bus idle speed and timing fluctuates |
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The engine was overhauled about 1500km ago. The Bus ran very well after the rebuild until one day we couldn't get it to start.
There was no spark so we assumed that the Petronix electronic ignition had failed so we put in a set of points instead, after which the Bus would run but not very well. We were unable to set the timing as per the specification for the dual vacuum distributor as the engine refused to run at 4.5 degrees retard.
We swapped the old DVDA for a remanufactured SVDA (from BusDepot). Now the Bus is drivable again but the idling is irregular. The mark on the pulley is not very stable when a timing light is connected and we also found that sometimes the timing is going off by about 4-5 degrees after taking a test drive. So we if set it to 7.5 degrees advanced and go for drive, it would be at 12 or 4 when we got back...
I suspected a vacuum leak but after going through all the hoses thoroughly we were still not able to find the issue...
Any ideas on what else we can check!?
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busdaddy
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Joined: February 12, 2004
Posts: 51150
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Sun Sep 17, 2017 9:28 am Post subject: Re: FI Bus idle speed and timing fluctuates |
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Hmmmm,,,,, at first glance it sounds like a bad distributor, how freely does the rotor spring back when you give it a little twist?
Large vacuum leaks do require more advance to stay running so a smoke test may be helpful: https://www.thesamba.com/vw/forum/viewtopic.php?t=620083
Another tiny possibility is the builder left out the key on the fan hub so the timing mark is moving, but that won't make it run bad suddenly, it only effects setting the timing.
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sjbartnik
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Joined: September 01, 2011
Posts: 5998
Location: Brooklyn
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| Posted: Sun Sep 17, 2017 9:56 am Post subject: Re: FI Bus idle speed and timing fluctuates |
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A vacuum leak cannot/will not affect the timing.
If your timing is jumping around it is most likely a problem with the distributor or distributor drive gear.
Changes in idle speed also don't affect the timing UNLESS the idle speed goes so high that the advance within the distributor starts to kick in.
I suspect that the idle is irregular because the timing is jumping around, not the other way around.
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SGKent 
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Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Sun Sep 17, 2017 11:57 am Post subject: Re: FI Bus idle speed and timing fluctuates |
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| I suspect that the idle is irregular because the timing is jumping around, not the other way around. |
x2. Sounds like you have a bad distributor. That said, replace the condenser and see if that makes any changes. One of the best tests would be to check the dwell and see where it is set, and if it is stable. Also I hope you put the spring back in the drive gear when you swapped distributors. If it isn't there the drive gear can walk up and down.
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Wildthings
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Joined: March 13, 2005
Posts: 50352
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| Posted: Sun Sep 17, 2017 12:37 pm Post subject: Re: FI Bus idle speed and timing fluctuates |
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| SGKent wrote: |
| Also I hope you put the spring back in the drive gear when you swapped distributors. If it isn't there the drive gear can walk up and down. |
This would be my guess as the problem has happened on more than one distributor. He likely also needs to lube the distributor he is using according to the manual.
The timing for all VW aircooled engines is 28° BTDC @3500+ rpms, hoses off and plugged. Forget the book timing unless you can find a brand new factory grate engine. |
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Wasted youth
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Joined: July 06, 2012
Posts: 5134
Location: California's Hot and Smoggy Central Valley
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| Posted: Sun Sep 17, 2017 1:02 pm Post subject: Re: FI Bus idle speed and timing fluctuates |
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Just out of curiosity...
With the engine off, reach in there and try to twist or turn Distributor by hand.
Does it move? |
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airschooled
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Joined: April 04, 2012
Posts: 12728
Location: on a bike ride somewhere
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| Posted: Sun Sep 17, 2017 2:28 pm Post subject: Re: FI Bus idle speed and timing fluctuates |
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I've dealt with the BusDepot rebuilt SVDA distributors twice, and both times they were very tight when new, but loosened up after a few thousand miles. Both distributors would "hang" above their proper idle timing until they fully broke in.
Timing scatter can be in the distributor, but it could also be excessive drive pinion play, excessive crankshaft end play, or a missing distributor sprig.
Robbie
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Tcash
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Santaji
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Joined: December 29, 2007
Posts: 105
Location: Mumbai, India
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| Posted: Wed Sep 20, 2017 12:34 am Post subject: Re: FI Bus idle speed and timing fluctuates |
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| SGKent wrote: |
| Also I hope you put the spring back in the drive gear when you swapped distributors. If it isn't there the drive gear can walk up and down. |
I think this spring has always been missing as we don't remember noticing any spring anytime while removing/installing the distributor. Will try sourcing the spring and putting it back in.
| busdaddy wrote: |
| Hmmmm,,,,, at first glance it sounds like a bad distributor, how freely does the rotor spring back when you give it a little twist? |
Checked both the distributors and lubricated them. On both the cam springs back correctly when twisted and the plate also moves when applying vacuum...
Now with the DVDA it ran but very roughly so we put the SVDA back again. The idle still changes occasionally but it's much better than the other distributor. After a test-drive the timing had advanced 4-5 degrees but returned to normal after restarting the engine....
| asiab3 wrote: |
I've dealt with the BusDepot rebuilt SVDA distributors twice, and both times they were very tight when new, but loosened up after a few thousand miles. Both distributors would "hang" above their proper idle timing until they fully broke in.
Timing scatter can be in the distributor, but it could also be excessive drive pinion play, excessive crankshaft end play, or a missing distributor sprig.
Robbie |
Hopefully it's just a combination of the spring being missing and the distributor needing to break in... Will report back after getting the spring!
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tommu
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Joined: November 15, 2011
Posts: 618
Location: L.A.
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| Posted: Wed Sep 20, 2017 10:58 pm Post subject: Re: FI Bus idle speed and timing fluctuates |
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| Santaji wrote: |
| SGKent wrote: |
| Also I hope you put the spring back in the drive gear when you swapped distributors. If it isn't there the drive gear can walk up and down. |
I think this spring has always been missing as we don't remember noticing any spring anytime while removing/installing the distributor. Will try sourcing the spring and putting it back in. |
Take a torch and look down the hole for the spring. You don't normally handle it when swapping distributors. I'm curious to know your idle speed. Maybe it's a little high and the mechanical advance weights are just starting to spin out causing the advance and idle speed to hang up there a little.
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SlowLane
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Joined: July 11, 2005
Posts: 1044
Location: Livermore, CA
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| Posted: Thu Sep 21, 2017 8:33 am Post subject: Re: FI Bus idle speed and timing fluctuates |
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| tommu wrote: |
Take a torch and ... |
Just to clarify for you 'mericans: "torch" is Brit-speak for flashlight, not your oxy-acetylene setup... 
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tommu
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Joined: November 15, 2011
Posts: 618
Location: L.A.
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| Posted: Thu Sep 21, 2017 4:03 pm Post subject: Re: FI Bus idle speed and timing fluctuates |
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| SlowLane wrote: |
| tommu wrote: |
Take a torch and ... |
Just to clarify for you 'mericans: "torch" is Brit-speak for flashlight, not your oxy-acetylene setup... |
OP is in India and will know the proper word. 
EDIT: re-read your comment and it really never crossed my mind that you lot only have one, very dangerous, kind of torch.
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