Vacuum gauge experts, opinions welcome for this readings (video)

[marc]

Hi. I don't stop by this tavern very often. It's been a long time since my fork spacers howto, and more.

My GS is now probably over 100.000Miles. (138.000Km shown on the counter, but the condition of the bike as I purchased it, 100.000Km ago, made me think that there are about 20.000Km missing in the counters)

Repaired, used, cared, and enjoyed this bike for a lot of years. But I guess It's getting old. 2qt/1000Miles oil consumption, camshaft chain is EOL, having some hesitation issues...

I know there are lots of knowledgeable people here.

Opinions welcome:

https://youtu.be/KcZJjIAk3ys

[herennow]

this is a good explanation of how to read a vacuum gauge  but you need flash...

http://www.secondchancegarage.com/public/186.cfm

[marc]

this is a good explanation of how to read a vacuum gauge  but you need flash...
http://www.secondchancegarage.com/public/186.cfm

Thanks for the link. Very nice and a valuable job for the author.
There is plenty of explanations in the net.
There's one with a PDF https://www.austincc.edu/wkibbe/vacuumtesting.pdf that is a good candidate to print and keep in the vacuum gauge box.

All them define "a good vacuum" as 15 to 22 inches. But Mine is about 6 at idle.
I can see other videos of people syncing carbs with a vacuum of 9 to 12 at idle.
https://youtu.be/Axllq9wNIRE?t=245
https://youtu.be/c-iHNyp1Lss?t=209
No leaks in intake boots: they are new, OEM, with new rubber seals.

Getting confused.

[herennow]

my notes say : balanced at  around 20 kpa vacuum at 1750 revs.

This is close to 6" mercury.

Most vacumms I've seen onoline have also been much higher but figured they were for cars. On another forms folks said it should be higher and when I pushed them for their measurements that had in fact never done any.......

My engines been around the block but has new rings a couple years ago and compression is great.

[Suzuki Stevo]

Vacuum Gauges are  used to show Carb Synchronization at an IDLE/or 1500 Rpm's (just above idle) so the carbs work as a team as you roll the throttle on. The farther you get away from an IDLE the LESS  Carb Synchronization matters.

Blipping the throttle or revving the engine doesn't show you anything....is that the answer you wanted or did I misunderstand the question?     

[marc]

Vacuum gauges reveal a lot of issues in the engines.
Of course if you use them just to balance, you only need to start the engine at idle, and set the screw so that both show the same.

But vacuum gauges also can reveal lack of compression, can reveal faulty valve seats, faulty valve springs, and some even know how to detect failures in timing.

Imagine a old engine, with a stuck ring or a leaky intake valve. If you balance carbs with the engine in this condition, you'd probably end with a nice idle but a poor midrange.


My knowledge is limited, so, what I can see in my video is:
- OK, idle is balanced
- balanced midrange
- balanced high
- I don't see needles doing weird things, hence, I think that valves are OK, no leaks.
- Weak valve springs can cause ressonance, and this could cause valves bouncing, that the gauge vould reveal. I guess I don't have weak springs.
- I don't have enough knowledge to see valve guides issues.
- I can't see any pressure drop at high RPM revealing a clogged exhaust.

The only issue I can see is the extremely low suction of 6 inches, where manuals show that it should be between 15 to 22. I can see other videos of people balancing carbs, and their suction is 9, and other are 12. This confuses me.