Vaccum reading. Valve guides?

[Noidea]

Hey all sharing someFindings I have. Ive Been having strange idle issues trying to figure out. I got the float height sight gauge sorted carbs seem good. So than I bought some glue in vacuum barbs from 650central so i can see the vacuum and what goin on with my idle these are my readings.
From what I’ve read and videos ive seen on vaccum reading seems like i have bad valve guides.
what do u guys suggest next step?
How can i check the valve guides themselves? With free play of the valve?
I dont see any measurement for that kind of thing.

Do I Replace all valve guides? Not just the bad ones?

And what else should i do if i decide to take the engine out and overhaul it?

Vacuum reading video

I have another engine sitting in my shed but i don't know the condition of it besides decent compression. Last i was told it ran but can never trust that.

 

[Kevin Werner]

Does it do the same when you switch left to right. I use a Carb Tune. It has restrictions inline to help stabilize the readings.

 

[Noidea]

Yes i also switched it to the other vacuum gauge i have thats in the video. I was met with the same result.

 

[Kevin Werner]

Do you have oil usage and a blue cloud on start-up? What do your gauges do when you set your idle up to 2000rpm.

 

[jpdevol]

In your video, the main things I see are 1) the idle speed is set too low (spec is 1200rpm) and 2) those are rather basic (cheap) gauges and (as Kevin says) lack a dampening device to get a better reading - suggest an aquarium air valve to dampen the pulses: https://www.ebay.com/itm/125812905564

Regarding the guages indicating a worn valve guide(s): Unless the engine is smoking or giving some other indication; I wouldn't worry about the guides. When synching carbs, I'm looking for relative balance between the guages readings rather than any actual level of vacuum

 

[Kevin Werner]

What @jpdevol said, low idle. That is why I asked about 2000 rpm. You seem to have Mikuni VM carbs. They work very well with XS650s. The can let the engine idle very slowly. What happens at a very low idle is you arerunning on battery voltage which my be depleted by the starter draw. I asked about 2000 rpm because at that level you will see steady flow through the carbs and a higher charging rate. Further, a slightly worn valve guide may not be a problem if you do not have an oil consumption problem. If you run 500 hundred mile days regularly you might have a concern...

 

[Noidea]

Thanks for response yall. Well no to the oil consumption and I don’t get any noticeable blue smoke when starting. In the video taken i was idling at about 1800 rpm. The gauge i have is a cheapo amazon one. ( got it just cause wanted to dual reading) I have better Matco one which you can see in that video behind the cheap set and it did the same thing the cheapo one did with the fluctuating needle. What does that reading i have signify?
Im also going to get a leak-down tester and confirm everything is sealing as it should.

 

[Noidea]

I forget to add details of the bike when making a new post.
Its a 73 motor
Running hhb pma cdi kit with capacitor no battery

Vm34 carbs
25 pilot
185 main
2.5 slides
1 to 1.5 turns on air screw
P-6 needle middle clip

extended pandemonium ya mama exhaust.

The issue i have with idling is intermittent popping from carbs and loss of power

When running my left cylinders exhuast is hot
But my right is not.
I have spark and seem to get each side running with dead cylinder method. However after setting cylinder and putting both plugs on and running engine the rpms are pretty high and i have to back them down a bunch.

 

[Noidea]

Still shot of my tach in the video

 

[jpdevol]

What does that reading i have signify?

The idle in the video is perhaps 900 - not 1800 - the tach in pic above appears to be from a Honda and may not read correctly. My current opinion is that the synch is off by a fair amount.

 

[Noidea]

interessting. Ok ill see what other tachs i have and compare. Didnt even think of the tach being off In regards to synching your probably right. I first bench synch the carbs making sure the throttle opens at the same time with the finger method. Than i make sure that they are open the same amount with the idle adjust screw. But when running the bike i need to switch the idle settings on the fly to get it to run right. Maybe my ear is off but I just do what i can to get it to idle lower and without holding the throttle.
Lack of confidence with tuning is what made me get tools to visualize the tune such as vacuum gauge and float height sight tube.

 

[Kevin Werner]

I have acquired a small digital tach online for ~$10. Handy to have. With VMs the sync procedure is 3 steps. First, warmed up at idle with someslack in the throttle cable at the handle bar , ~1200rpm, sync left and right with idle adjust screws. Then, roll on the throttle to insure both carbs pull equally side to side. Adjust this with carb top cable adjusters. Finally, remove the remaining slack from the cable at the handlebar.