No vacuum at all on carb #3?

[Heavy Armor]

So this is a Mr. Leo carb set, and I have had NOTHING but trouble out of it. I finally had to disassemble it, and discovered that whoever put it together last had used some kind of nasty glue on the bowl gaskets, and maybe wiped it with a fibrous cloth that left a bunch of fuzzy crap around the edges inside and outside the bowl. The main jet finally sucked in a chunk of it and clogged. Got that cleaned up 100% and put it back together.

I now have ZERO vacuum on carb #3. My Carbtune isn't even wiggling. I double checked the diaphragm and it looks fine. I know the bowl and the jets are spotless.

What the heck happened???? I am SO. TIRED. of working on this.

[Nails]

I don't really get it. I don't see how one could get zero vacuum short of leaving off the carb entirely, and I don't really think that would do it. My bike didn't even have an idle miss with the caps on the vacuum testing ports entirely missing (rotted off). I certainly don't see how a clogged main jet could be responsible. If you're referring to the carb slide diaphragm, it responds to the velocity of air moving through the throat of the carb. It doesn't really have anything to do with vacuum, and sure doesn't cause any intake vacuum.

Do you feel a vacuum when you put a finger on the open port?

Yeah, I prefer not to use sealant on the float-bowl gaskets, mostly because more than the slightest smear can interfere with the float movement -- a very tight clearance. Ask me how I know. Did you find that nasty stuff on the other carbs?

Mr. Leo has a sterling reputation around here; and my limited interaction with him is consistent with that. Maybe you were accidentally shipped a carb set coming in instead of one he intended to ship out? Dunno.

[Heavy Armor]

Yeah the no vacuum is freaking me out, because the only thing I can think of is catastrophic piston failure, but it WAS working before I took the carb off (just not well), so I doubt that's the case unless I am the unluckiest SOB in the world. Throttle hangs like it's a vacuum leak, but it would have to be massive to show no vacuum, and everything looks correctly installed.

I spent all afternoon putting it back together, so confident that I had fixed the issue. Pretty frikkin heartbreaking. I've been screwing around with this thing for 2 years now, because I got shafted on the purchase and just don't have enough time to dedicate to the mess I wound up with. Probably haven't ridden it over 100 miles yet. Getting really sour on the whole brand at this point, with the massive PITA it is to take thing on and off (unreasonable, but nonetheless...).

[triton28]

The point of attachment for synchronizing gauges is downstream of the throttle plate so anything upstream of the throttle plate would have no effect on vacuum as Nails outlined. Unless of course if the #3 throttle plate is somehow disconnected from #4 throttle plate and is wide open; highly unlikely though.
If you are sure the throttle plate is not wide open and still connected to #4 throttle plate linkage as designed then I would recommend doing a compression gauge test across the board on all cylinders.
It could be a stuck ring/s or bad/unseated valve/s in #3 and the test would tell you which condition it is should either be the case.
But without the test everything else is just a guess. My guess is something with the rubber carburetor holder is not right.
Who knows, hopefully you will get 150 or more lbs on all 4 and that would preclude any kind of tear down of the engine at least.
If you get good compression readings within 10% of each other then what you have is a real mystery.
Are you sure the hoses of the gauges are OK? Just an obvious thought to look at.
Dave

[Nails]

Throttle hangs like it's a vacuum leak

I've had trouble getting a good slow idle -- sometimes hard to adjust between slightly high and almost stalling. Maybe that's what you mean by "throttle hangs"?

CV carbs are awfully temperamental, and things like fuel levels in the float bowl are critical. Maybe a vacuum leak, but that isn't really my first guess.

Pretty frikkin heartbreaking.

I recognize that sentiment. But after sorting through my bike, which has been a serious maintenance wreck (I never should've bought it), I've posted several sweet ride reports here.

I'm about to dive into it again, starting with swapping the head and maybe ending with why it stranded me in South Dakota a couple years ago. After several major delays, I'm finally finishing my shop (building the canopy over the barn doors), to start on an astonishing backlog of vehicle work.

After seeing the sweet XIIs often posted here, I'd have to recommend only buying a well-sorted one. I'd have been much better off ... except I didn't have the spare change at the time. OTOH, I didn't stand to lose much trying some hack mods that I would hesitate to do on a nice XII; and I like my mods.

[Heavy Armor]

GOOD NEWS! I have compression. Turns out it was just my Carbtune acting up, which was weird because it's literally only the 2nd time I've used it. When I swapped the hoses around, #3 was acting fine. The little weight had gotten wedged somehow... I had to turn it upside down and shake it out, then everything went back to working. I should have swapped the hoses to begin with, but I was too distraught after spending so much effort to get the carbs back in.

[cushman eagle]

That is good news,HEAVY ARMOR
That is like me trying to diagnose a tractors electrical problem before I check my test light

[Nails]

Proving once again that we shouldn't necessarily believe everything we think.