Carburetor Vacuum Reading Way Off

[jhorgan24]

I've been trying to figure out why my 1995 VS800 hasn't ran right in 5 years. It got stolen and then abandoned in a parking lot a year so really anything is on the table. I can usually get it started with enough time and patience but it doesn't ride like it did 10 years. It has way less power, way harder to start, and never sounds quite right when it's idling. I honestly don't take it more than 5 minutes away from my parents since I can't trust that it's not going to break down on me.

I've taken the carbs off and cleaned them a ton over the years without much thought to keeping the linkages the same so figured it's time to do a carb sync but when I hooked up the gauges I'm getting some really weird readings from the front carb. I seem to get normal vacuum on the rear carb but nearly none on the back carb. I thought that maybe there was a leak on those black rubber boots that connect the carb to the engine but that's pretty snug (although I've futzed with it enough that maybe it's worth trying to replace it anyway). I tried swapping the connectors and gauges around to see if it was a connector or gauge issue but I get the same reading so matter how I swap them. I've owned the bike for 15 years and I've never done a compression test so I'm wondering if that's the next thing I should try to rule out any internal engine issue. I also have a spare front carb from a parts bike I got years back. It'll need some cleaning and I'll need to swap some parts around but figure changing that out might help narrow it down. I rebuilt the carbs last summer so it's possible I screwed something up there but after I got the weird gauge reading last summer I removed the carb, cleaned them and inspected all the gaskets, put it back on and got the same result.

I took some videos of the gauges last year when I was working on it and then another video this past weekend.
2023:
2024:

If anyone has some theories on what could be the problem here it would be much appreciated!

[sgtcall]

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[Herb]

General information. The one with the lowest reading is doing all the work, the other one is just along for the ride.

Either adjust the low cyl to pull more, make the throttle cable shorter, or make the high reading one cable longer. The distance betwen the throttle lever and the adjuster is what you need to work with.

[jhorgan24]

General information. The one with the lowest reading is doing all the work, the other one is just along for the ride.

Either adjust the low cyl to pull more, make the throttle cable shorter, or make the high reading one cable longer. The distance betwen the throttle lever and the adjuster is what you need to work with.

Gotcha, so this isn't necessarily a symptom of anything terribly wrong with my bike, the carbs are probably just even more out of whack than usual? I think I've tried adjusting them before last summer but can't say for certain. I'll give it another try this weekend.

Appreciate the advice!

[Herb]

General information. The one with the lowest reading is doing all the work, the other one is just along for the ride.

Either adjust the low cyl to pull more, make the throttle cable shorter, or make the high reading one cable longer. The distance betwen the throttle lever and the adjuster is what you need to work with.

Gotcha, so this isn't necessarily a symptom of anything terribly wrong with my bike, the carbs are probably just even more out of whack than usual? I think I've tried adjusting them before last summer but can't say for certain. I'll give it another try this weekend.

Appreciate the advice!

BTW, Not sure if I was clear about the adjuster to the throttle plate lever. We are talking about the adjustment at the carb.

[FallenAngel]

The bouncy needle suggests a bad bad valve sealing in the seat or a posable vacuum leak
Show a video concentrating on the vacuum gauges
Close enough to read the measurement would be very helpful
Rev the engine and hold so we can see where the needle steady's at and so we can read the vacuum
Place a peace of paper at the exhaust tip of each pipe let us know if it gets sucked into the pipe or if the exhaust pushes it away
Also A heat measurement at the head is ideal or you can just place your hand at the exhaust tips

Also it being a liquid cooled bike do you have coolant in the system

Not trying to suggest your ignerent in ant way this is just stuff I would do if you brought it to me to look at