Vacuum Question - Vac Advance
06-15-08, 11:15 PM
#1
djessence
Thread Starter
Vacuum Question - Vac Advance
So finally got my new rebuild started, running, timed and whatnot after a few difficulties (like e-shaft pulley being 90* off).
In piston engines (i know) you can use a vacuum guage to try and find the "prime" mixture on the carb. Highest vacuum is supposedly the best mixture.
Firsty i noticed something strange and that was the vacuum guage reads like 0 until about 2000 rpm, even though you can feel the vacuum from where i plugged into. And when it does read it reads in the "ign timing error zone" even though my timing is bang on at idle.
Anyways I digress.
I originally tried pulling the vac advance hose for the distributer off and using that but there was NO vacuum whatsoever. Pulled the hose off and the car didnt even do anything, no feelable pull or anything off of it.
Is this normal? I havent had a chance to re-check timing and the advance because i broke my timing light.
And any ideas about the vacuum guage?
In piston engines (i know) you can use a vacuum guage to try and find the "prime" mixture on the carb. Highest vacuum is supposedly the best mixture.
Firsty i noticed something strange and that was the vacuum guage reads like 0 until about 2000 rpm, even though you can feel the vacuum from where i plugged into. And when it does read it reads in the "ign timing error zone" even though my timing is bang on at idle.
Anyways I digress.
I originally tried pulling the vac advance hose for the distributer off and using that but there was NO vacuum whatsoever. Pulled the hose off and the car didnt even do anything, no feelable pull or anything off of it.
Is this normal? I havent had a chance to re-check timing and the advance because i broke my timing light.
And any ideas about the vacuum guage?
06-15-08, 11:29 PM
#4
djessence
Thread Starter
Dam i knew I forgot something.
It is a fresh rebuilt Stock Port 12A. No Rats Nest. Followed the tutorial and capped everything I didnt need. Kept a few things like vac advance obviously. Or at least I have it hooked up to second from the left (i believe)
For when we actually got Vacuum we used (in picture because i honestly dont know what it is)
We ended up using the vacuum guage reading to tune, just to where the highest was, and then used the technique sterling used in his tutorials on tuning. They were pretty close, i was more interested in why my vac advance doesnt seem to be pulling vacuum, and curious about the guage.
I should also ad, after we did this it seems to pull hard (havent had it above 4k rpm yet) doesnt stall on decel like it did before tuning and idles nicely at 750.
It is a fresh rebuilt Stock Port 12A. No Rats Nest. Followed the tutorial and capped everything I didnt need. Kept a few things like vac advance obviously. Or at least I have it hooked up to second from the left (i believe)
For when we actually got Vacuum we used (in picture because i honestly dont know what it is)
We ended up using the vacuum guage reading to tune, just to where the highest was, and then used the technique sterling used in his tutorials on tuning. They were pretty close, i was more interested in why my vac advance doesnt seem to be pulling vacuum, and curious about the guage.
I should also ad, after we did this it seems to pull hard (havent had it above 4k rpm yet) doesnt stall on decel like it did before tuning and idles nicely at 750.
06-15-08, 11:40 PM
#6
djessence
Thread Starter
I think that hose has something to do with choke maybe.
Tough to say, I guess when Im back in Calgary Ill fix/get another timing light and check the advance.
We picked that hose because it was pulling strong vacuum and it was easy to get off. The vacuum plugs were on super tight.
Tough to say, I guess when Im back in Calgary Ill fix/get another timing light and check the advance.
We picked that hose because it was pulling strong vacuum and it was easy to get off. The vacuum plugs were on super tight.
06-16-08, 10:10 AM
#7
Lives on the Forum
There have been huge arguments waged over which nipple to use, and why. The difference is between manifod vacuum (present at any time that the engine is running, but diminshing with rpms), and ported vacuum (present only when the throttle opens).
I run my vacuum advance to the nipple farthest forward on the base of the carb, which I believe is ported vacuum. This should (theoretically) provide advance once you tip into the throttle. I've been running this way for about 18 months now, and the car feels a lot stronger at partial throttle than it did using a different port.
Anyway, that's what seems to work best for my carb. And I've received PMs from others that I have advised on this, stating that the car was much improved after making the change.
Hope this helps...
I run my vacuum advance to the nipple farthest forward on the base of the carb, which I believe is ported vacuum. This should (theoretically) provide advance once you tip into the throttle. I've been running this way for about 18 months now, and the car feels a lot stronger at partial throttle than it did using a different port.
Anyway, that's what seems to work best for my carb. And I've received PMs from others that I have advised on this, stating that the car was much improved after making the change.
Hope this helps...
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06-16-08, 10:24 AM
#8
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The factory setup uses the 2nd port for vacuum advance.
There should be zero vacuum to the advance at idle, and increasing vacuum as the throttle is opened. If you have vacuum at the advance at idle, it will actually retard the the timing as the throttle is opened, rather than advancing it.
As for finding a manifold vacuum port, which is what you need to use for tuning on the carb, check that tutorial guide for the port it says to use for the A/C and cruise (if retained). That port *should* have manifold vacuum.
There should be zero vacuum to the advance at idle, and increasing vacuum as the throttle is opened. If you have vacuum at the advance at idle, it will actually retard the the timing as the throttle is opened, rather than advancing it.
As for finding a manifold vacuum port, which is what you need to use for tuning on the carb, check that tutorial guide for the port it says to use for the A/C and cruise (if retained). That port *should* have manifold vacuum.
06-17-08, 08:17 PM
#11
djessence
Thread Starter
Haha of course you can?
I will give you a heads up I am young and newerish to the rotary game...but it RUNS!!!!
Sure shoot me a pm or email (shields8@gmail.com) and I'll share/answer/ponder etc with you.
I will give you a heads up I am young and newerish to the rotary game...but it RUNS!!!!
Sure shoot me a pm or email (shields8@gmail.com) and I'll share/answer/ponder etc with you.
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