Vaccum unit

Post subject: Vaccum unit Posted: Tue Feb 13, 2007 06:26 AM

Hi
Can anybody help me. I have just been checking my timing, which I had to adjust as the acceleration was garbage.
My VW is a bit odd. It had F.I, but now a carb, with a breakerless point distributor, which were installed before I got it. I have had both items replaced.
What exactly is the vaccum unit for, because with the timing light attached and the vaccum hose disconected and I rev the engine the timing mark moves, with the hose connected the timing mark moves?
Is the unit faulty? I always thought that the vaccum unit stopped the mark from moving.
Anyway, and help is appreciated.
Andrew from Mexico. Oh yes, my VW (vocho) is a '96

Post subject: Re: Vaccum unit Posted: Wed Feb 14, 2007 04:17 AM

when you disconnect the vacuum line you are setting the timing for the centrifical advance inside your dist. then you reconnect the vacuum and time it again for the setting you want.

what is it timed at without vacuum? With vacuum?

Post subject: Re: Vaccum unit Posted: Wed Feb 14, 2007 04:37 PM

ajeden wrote:

What exactly is the vaccum unit for, because with the timing light attached and the vaccum hose disconected and I rev the engine the timing mark moves, with the hose connected the timing mark moves?
Is the unit faulty? I always thought that the vaccum unit stopped the mark from moving.

W/vacuum disconnected-plugged, you are setting base idle. The timing moves due to mechanical advance built into the dist.

W/vacuum connected, you are setting total timing once the advance is "all in" for instance in a v8, you have 8 deg BTDC at idle; then 34 deg BTDC all in by 2500 rpm.

Hope that helps with your understanding. Cool

Post subject: Re: Vaccum unit Posted: Wed Feb 14, 2007 09:37 PM

Hi
Thanks for the replies.
So, with the vaccum pipe removed and pluged. once the timing is set using the light, if you rev the engine the timing marks stay still?
And with the pipe connected, and rev the engine the timing marks move, because the advance mec kicks in?
It's that my timing marks move, whilst reving the engine, with the pipe disconected and connected.
Is there a way to test the vaccum/advance unit.
Thanks

Post subject: Re: Vaccum unit Posted: Thu Feb 15, 2007 12:19 AM

Yes it will move w/vacuum plugged, but not as much. That is the mechanical advance built into the dist..

When running, you can plug a vacuum pump into the nipple on vacuum advance and build vacuum, that will test the advance. Cool

Post subject: Re: Vaccum unit Posted: Thu Feb 15, 2007 12:26 AM

with vacuum disconnected the mark will move until you are at full advance then it should stop even when bringing the rpms up.

on my car right now its timed at 28* without vacuum..it wont go past 28 with the vaccum line off. then i put the line on and time it again, adjust the vacuum and its at about 40*

Post subject: Re: Vaccum unit Posted: Thu Feb 15, 2007 06:45 AM

Hi Guys
Thanks a million. I think then my advance is not 100%
Will investigate further
Thanks again
Andrew