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

[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!

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

Well, the good news is that I managed to sync the carbs perfectly! Or damn near close enough anyway. The old throttle cables were impossible to work with and already breaking out of their casing so I replaced that and everything was gravy for all of about 30 minutes.

Took a ride out to test it out, had to fill up on gas and shortly after that I suddenly lost about half the power of my bike. I managed to get it home by taking it real easy on the throttle but when I pulled into the driveway I left the bike running to inspect it and found white smoke coming out the exhaust. Everything that I've read points to coolant getting into the engine and the head gasket needing to be replaced. I checked the coolant and it was a bit low but not by too much. Couldn't find any trace of oil in the coolant but I read it can get into the engine anyway.

I did a quick check on the coolant hoses but didnt notice any leaks. Doesn't seem like I can get at the engine head without taking the engine off the entire bike. Does that sound right? Probably should have done a compression test for shits and giggles while I had the bike out but forgot. Not sure if that will indicate if anything else is wrong. I'm debating if I should try and take the bike to a shop to replace the head gasket or try and do it myself. I've worked on nearly everything else on the bike but I'm a bit wary of taking the entire engine out. If I do replace the head gasket is there anything else I should do to the bike while the engine is out? I also read about K-Seal, debating if that's worth trying first.

[navigator]

The engine does have to come out to pull the head...but before you gut it, do some more checks.
Compression check will be low if the head gasket is bad. It takes a lot of water to blow white smoke, if you coolant is not very low, look elsewhere.
I suspect you lost spark to one hole and the white smoke is condensed unburned gas.

[jhorgan24]

Sounds good, I'll check both out this weekend. Meant to do a compression check anyway before buttoning everything up last weekend.

I put my hand near both exhausts, only one was blowing the smoke, and I don't recall smelling gas. At least not any more than usual. Hoping that it's something easy like not having spark but with my luck, that's probably not it.

Anything else I should check on while I have it out? I could drain the oil and check for coolant in there but there really wasn't too much coolant missing when I checked. I think I filled it all the way up to the top last summer or the summer before and it was maybe an 1/2-3/4 of an inch below that when I checked last Sunday.

[jhorgan24]

I just did a compression test and both cylinders read 100psi. I'll need to pull up the manual but I'm pretty sure it's supposed to be closer to 150 so something is already not great. I also expected the front cylinder to be fine and the rear one to be low. I didn't expect them to be the same. I might try with a different gauge just to be sure. It's brand new but you never know.

I also held the spark plug boot with the spark plug in it (away from the bike) while doing the compression test to see if I could see a spark but no dice on either. I'm probably doing something wrong there but will check that

[navigator]

The throttle must be held wide open to perform a compression check.
The body of the plug needs to be grounded to the engine to see any spark.

[jhorgan24]

I definitely forgot to hold the throttle open, thanks for the reminder! Doing that I managed to get 120 psi on the rear cylinder and 130 psi on the front cylinder. I think I'll hook the charger up to the battery, warm up the bike and run the test once more to get the most accurate reading.

I tried touching the spark plug to the pipes to try and get a spark but no dice on either. Even watched a video to make sure I wasn't doing anything stupid, although it's no guarantee! It's a bright day and I'm working in the sun so will try again later when the sun isn't overhead, although if I'm really not getting a spark I won't be able to get the bike warmed up later anyway

[jhorgan24]

Took another crack at it after having the battery charge and doing the compression test after warming it up, still ended up with about 125 for both. Checked the manual and the lower end is 185, so that's pretty not good. Should have done a wet test as well while I had everything setup but considering the white smoke I'm not optimistic that would have helped. I did manage to confirm spark in both cylinders though which was good.

For the most part it sounds really great but the white smoke worries me and it randomly losing power makes me worried to take it more than 10 minutes away from home. I'm wondering if it's worth taking to a shop at this point or if it's worth trying one of those head gasket sealants although that feels like I'd just be kicking the can down the road.

My only other thought is that I do have a spare engine from a parts bike, the odometer says that it's only a few thousand miles although I have no idea if that's accurate. The bike was also sitting for a long time in some dudes yard so I have no guarantee that it's better than what I've currently got in there. So far the only thing I know for certain is that I can get it to crank since I swapped the starter clutch out of it a few summers ago.