Ported vacuum for vac advance

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

I think I get it now. Any port that is below the throttle butterfly will give you manifold vacuum. Above the throttle butterfly will give you "ported" vacuum.
So...once again I have been the disseminator of B-A-A-A-D information.
In the above picture, the port you can't see when the throttle is closed is the ported vacuum.



Always listed to PinHead.


Never listen to me....


Ed
 
Degnol said:
So the other (above) the throttle butterfly is the ported vacuum? OK.
Click to expand...

Maybe this?

Just were does that little tube end up? Try spraying some carb cleaner in the brass tube and see where it comes out.

attachment.php

Enginerebuild0.webp
 
THAT'S IT! I just ran a piece of ss wire, had to go from the inside to the outside, but that is where it exits. Must admit, I never even saw that little hole.
That would be a bitch of a mod to do, IMHO, and I drill little holes all day.


Now, Charlie, how about my piston question????




Thanks,
Ed
 
Thanks. I wasn't sure that there was a hole there, but it is hard to drill one anywhere but straight. There are lots of tiny holes in carbs that are important.

I don't know about the piston question. They can have all kinds of crazy marks on them or none at all. I would just go ahead and mic it anyway to be sure. You can just mic the bore and see if that is .030 over.
 
Good luck to you, I learned a lot, I think everyone who read this did. PinHead always knows and speaks truth from experience. I'm going to switch throttle bodies on my carb and set new records.

Good post!


Ed
 
Degnol said:
Good luck to you, I learned a lot, I think everyone who read this did. PinHead always knows and speaks truth from experience. I'm going to switch throttle bodies on my carb and set new records.

Good post!


Ed
Click to expand...

Geez, you're killing me Ed. :o

Are you going to tell your wife that you are taking advice from a Pin Head?

Actually I though I made it pretty clear that I was guessing about the location. I'm a Solex carb guy, so all I knew is it had to be above the throttle plate.
 
Pin_Head said:
Geez, you're killing me Ed. :o

Are you going to tell your wife that you are taking advice from a Pin Head?
Click to expand...


She already knows. I told her you've already save me time and $$$. So she spent the $$$. Then she left town with the digicam, called me and asked me how to use it.


Up until this post I thought any port on which the hose would fit was good-to-go.
This might explain why my HEI vacuum is up against the oil filter.

If you don't want the occaisional compliment, then quit being right.

I do appreciate all the help and advice.


Ed
 
might be a while before I get it all back together and test it , the helicopter company I work for is sending me away for a week. I'll definately let all you guys know how it works when I finally get it done.
 
Ideally there should be no vacuum at idle and substantial vacuum (>5") just above idle. The vac advance on the Denso distributor doesn't start to move 'til ~6" vacuum and is all in by 12".
 
The vacuum at the port depends on the velocity of the air past it. This is a function of the engine RPM and the area of the throttle opening. Higher RPM and narrower throttle give more vacuum. As you open the throttle wider under load, the vacuum goes down and the spark retards to avoid preignition.
 
landcruiserrich said:
So around what rpm should vacuum start reaching 5"? Will there be more vacuum under load?
Click to expand...
You are mixing up vacuum advance and centrifugal advance. Cent. advance will start coming in at a set RPM.

Ported vacuum will vary depending on throttle position, load, RPM. Oh, and if the ported vac fitting was installed higher or lower will affect when it produces vacuum.
 
The port ended up a little higher so that could explain why the vacuum doesn't kick in right after idle. I'll stick the vacuum gauge on it again, but it looks like I'm going to need another carb base with ported vacuum installed already. How much would just a carb base like that cost?
 
You must log in or register to reply here.

Share this page

Back
Top Bottom