pickup's vacuum line

[XSokieSPECIAL]

Thank you motoman and Ken. I don't know where Randy got the idea as to how the vacuum ADVANCE works.

No hard feelings Randy but your thinking was pretty much backwards. However, you did teach me the proper way to spell "vacuum" .

Eddie--- follow the instructions I gave in post #9 to make sure everything is working properly.

[Flatlander]

Not meaning to hijack the thread here......but wouldn't running pod filters instead of the air box, create a much more irattic pulse on the advancing mechanism, because with pods you are just sensing the #2 carb only and with the air box you are monitoring all 4 carbs to some deg.?
And running a more free flowing after market filter in the air box, it won't allow "design" vacuum on the adv. port (like the jets)? So....possibly not advancing properly.......to design anyway???

Anybody got a shelf full of factory filters and air boxes???

[cywelchjr]

Not meaning to hijack the thread here......but wouldn't running pod filters instead of the air box, create a much more irattic pulse on the advancing mechanism, because with pods you are just sensing the #2 carb only and with the air box you are monitoring all 4 carbs to some deg.?
And running a more free flowing after market filter in the air box, it won't allow "design" vacuum on the adv. port (like the jets)? So....possibly not advancing properly.......to design anyway???

Anybody got a shelf full of factory filters and air boxes???

That would be no, because the vacuum port for the advance is between the butterfly and the CV slides, which is a vacuum region of the carb. Only if the air flow has reached a point of being faster than the engine can use (which lowers vacuum) does the vacuum go down there. Pod filters and such have no affect and yes, the port always senses only the vacuum on the #2 carb.

[randy]

Thank you, Ken, for making my point.

But then there's also 16 degrees built into the vacuum-advance device, and that pulls the timing around to 52 degrees BTC when the bike is cruising along at freeway speeds. Wind the throttles open, and it drops back to the power-setting

roll off throttle, and it auto-advances for economy;

So, throttle open = retard, throttle closed = advanced.

[Flatlander]

LOL......I forgot about the cv slides.....OOOOPPPSS!!!

You Guys rock! Thanks for setting that staight!

[XSokieSPECIAL]

[QUOTE

so, throttle open = retard, throttle closed = advanced.[/QUOTE]

Only in new yawk

[Ken Talbot]

Here's a couple of pictures to help illustrate what Randy is saying, what the magazine article is saying, and how the "vacuum" device works.

First, here is the brass nipple on the body of carb #2:


Next, here's where the orifice enters the carb throat:


Note - the orifice is located behind the closed butterfly (i.e. between the butterfly and the intake valve), where there is in fact a notch in the back side of the butterfly. With the butterfly completely closed, the orifice would appear to be almost cut off. However, with just the slightest amount of butterfly opening, the orifice is uncovered, there is maximum vacuum applied to the orifice, which makes the vacuum assembly pull the advance around to the mentioned total maximum 52 degrees of advance. This "slightest amount of butterfly opening" would be what exists at idle. At idle, there should be plenty of vacuum at the nipple.

As you crank the throttle, the butterflys open more, and the vacuum at the orifice drops. This causes the advance assembly to retard the timing, back towards the 36 degree total of built-in static plus maximum centrifugal.

Randy's got it right...

[crazy steve]

Randy has it right, but his terminology isn't quite right. Any vacuum port between the throttle plate(s) and the intake valve(s) is considered MANIFOLD vacuum. More vacuum the less throttle opening you have. This set-up will give the best performance and increase fuel economy at lower loads, as was stated in the Cycle article.

PORTED vacuum is a port between the AC and the throttle plate. Works exactly the opposite; the more throttle opening, the more vacuum. This type of ignition advance is used almost exclusively for emissions purposes, as this causes higher combustion temps. But it will also lead to detonation and overheating. This was used on cars (and still may be) a lot in the late 60s and up, but was usually controlled by a heat-operated vacuum 'switch' to go back to manifold vacuum when the motor started to get too hot.

'78E original owner

[Flatlander]

AND...... I forgot about the notched butterflies!
Thank you for the pictures Ken and everyones explination on this! This really sent me down the wrong thought path/process at first. Cleared up now....Thanks again all!
Even if the hole is partially covered...or on the other side of the butterfly (opposite of intake valve) it still has the CV to help create vacuum.
Really getting a better understanding on these carbs and the inportance to a good clean and tuned carb system.

[XSokieSPECIAL]

Alright, I will concede the point. I will NOT admit I am wrong though. There is STILL no vac at idle and manifold vac, whatever that may be due to engine load, off idle.

However, this thread was started by Eddy Gravy because HE is having a problem and I think we have hijacked this thread long enough with this little sparring session. Don't you?

Please, read Eddy's posts and lets get back to HIS question.

Good day gentlemen

[randy]

Okie, you did answer Eddy's question:

When it's hooked to the CARB itself like it's supposed to be. I should only move when you open the throttle.

You had it correct, the only misinterpretation was that the movement of the plate that you see when going off-idle is not an advance, but actually a retard.

[XSokieSPECIAL]

Okie, you did answer Eddy's question:



You had it correct, the only misinterpretation was that the movement of the plate that you see when going off-idle is not an advance, but actually a retard.

Randy, please do us both a favor. Pull your ignition cover, attach a timing light to your engine, start the engine, apply vacuum to the diaphragm either manually or by cracking the throttle, or even better yet push the diaphragm in with your finger, and see which way the timing mark moves by using the timing light.

THAT is all I have to say on this subject.

[randy]

THAT is all I have to say on this subject.

Thank you. I'm done with this also.

[skids]

Gee, everyone wants the last word. I am done with this also!

Skids <-- contributed absolutely nothing! :-)

[XSokieSPECIAL]

Gee, everyone wants the last word. I am done with this also!

Skids <-- contributed absolutely nothing! :-)

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