'78 kz1000 -- where's the vacuum line hookup?

I looked in the manual but can't find this.

The petcock on a 1978 kz1000 has 3 nipples -- two are for supplying gas to the bank of carbs, and one nipple is slightly smaller and is the 'vacuum line' that operates the vacuum diaphragm in the petcock.

The way this apparently works is: when the petcock selector is 'On' or 'Reserve' no gas will flow unless the engine is running. This way, when you park your bike, you can just leave the petcock 'On' or 'Reserve' and no gas flows from the tank into the carbs.

They pulled this off by putting a diaphragm inside the petcock. It's kept closed by a spring and when the vacuum is acting, the spring is overcome, the diaphragm opens, and gas flows.

So this vacuum line comes from somewhere on the engine or the carbs -- I DON'T KNOW WHERE.

I pulled the carbs off for cleaning, and I see the 2 nipples supplying the gas from petcock to the carbs -- these 2 nipples are between carbs #1 and #2, and between carbs #3 and #4.

Then there are 3 other nipples on 3 of the 4 carbs (carb #2, #3, #4) pointing to the rear and upward at an angle.

Can someone tell me if these three upward/rear-pointing nipples are the vacuum for the one nipple on the petcock?

I think the answer must be 'no, those 3 upward/rear-pointing nipples are NOT for the vacuum line for the petcock since the petcock only has one vacuum nipple.'

I think you can tell I'm a tard in this area.

Help is appreciated -- where do I hook up the petcock's vacuum nipple to?

the vacuam fitting is in the carbs i haven't used a stock petcock for so long i forget ecxactly which nipple but i think it is between no 3 and no 4 if your engine is running it will be easy to tell fire it up and put your thumb over the nipples the one that changes the way it idles is it. the other two are for bowl vents. actually i don't use stock carbs at all.

Here's a picture of a carb set that has a separate vacuum nipple (yellow) for the petcock. Being in addition to the four "sync" vacuum nipples (one on each carb holder) which are capped during normal operation.

Some carbs do not have this 5th vac nipple, and just use one of the 4 sync nipples as a vacuum nipple to the petcock.

Good Luck!

[Click on image to enhance view]

thank's buddy i'm getting old sometimes i forget.wheres my key's has anybody seen my key's?

timebomb33 wrote:

thank's buddy i'm getting old sometimes i forget.wheres my key's has anybody seen my key's?

Hasn't happened to me yet, Knock-On-Wood!



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Somebody at the door?? :laugh: :laugh: :laugh:

Patton wrote:

Here's a picture of a carb set that has a separate vacuum nipple (yellow) for the petcock. Being in addition to the four "sync" vacuum nipples (one on each carb holder) which are capped during normal operation.

Some carbs do not have this 5th vac nipple, and just use one of the 4 sync nipples as a vacuum nipple to the petcock.

Good Luck!

[Click on image to enhance view]

That picture shows a carb bank similar but not identical to my stock '78 kz1000 carbs -- in the photo, your #3 carb has a cap where my #3 carb has a upward-angled nipple (your capped-off outlet on your #3 carb is under your rightmost green line) -- your bank of carbs has this type of nipple only on carbs #2 and #4. My carb bank has a nipple on #2, #4, *and* the #3 carb too.

Got me thinkin' though.

My #1 and #2 carbs are connected with a small (horizontal) piece of black rubber hosing, and the nipple on the #2 carb is right in that area.

My #3 and #4 carbs are *also* connected by a horizontal black hose, and the rightmost nipple on the #4 carb is in that area.

But the middle nipple, the one your #3 carb has blanked off, this nipple just sticks upward and there is no horizontal black hose in that area connecting carbs #2 and #3.

NOTE: your fuel intake is a single 'T' between your #2 and #3 carbs, and your carbs then have black hose to route the gas from #2 to #1, and from #3 to #4.
My carbs have two 'T's for the gas input: one between carbs #1 and #2, and one between #3 and #4. And those are NOT the horizontal black hoses I mentioned above.

I think the upward-pointing nipple on the #3 carb might be my vacuum hose, but.....

HELL IF I KNOW. I just can't figure out why the durned shop manual, the official Kaw 1978 kz1000 shop manual, has seen fit to sit on my desk and laugh its ass off at me on this particular issue of great importance. It is a mind-bending catastrophe of global import, apparently, a problem well qualified for solution, a curable condition that, were it not for the short sightedness of various and otherwise worthy Japanese-to-English translators -- would not find me so ready to smash my big toe with a sledge hammer out of rabid frustration, a large metal mallet which for the moment I seem to have misplaced.

Thanks for your help, it got me thinking about those 3 nipples sticking upward again.

get it running and stick your thumb over each nipple and see which one has vacuam that will be the one. that was easy heh.

Here's a pic of my 1976 KZ900-B1 LTD carb showing one of the two floatbowl vent hoses.

These are Mikuni manual slide carbs with 2 fuel pipes (intakes), 4 floatbowl overflow drain hoses, 2 floatbowl vent hoses, and 4 capped sync nipples. This bike has a manual (non-vacuum petcock), so there's no 5th dedicated vac nipple.

The factory routing was for the two vent hoses to run from the carbs through the frame opening and to underneath the seat where they clipped onto top of the airbox lid.

Some owners prefer to route the two vent hoses down between the frame and swingarm (along with the 4 overflow hoses) to exit underneath the bike.

More pics to follow.

Here's a pic of the two carb floatbowl vent hoses affixed to the clips built into the airbox lid.

timebomb33 wrote:

get it running and stick your thumb over each nipple and see which one has vacuam that will be the one. that was easy heh.

Reckon I needed to have that thrown out there twice before I had a moment of unorthodox Genius, I need to admit here those times are as rare in my mental activities as a ricochet in a pillow fact'ry.

So here's how I used Mr. Bomb's advice: I thought "well, the durned carbs are off the bike on account a, I had to clean 'em. And, even though I'm feeling a bit on the lazy side right now -- them carbs is only 5 feet away from me next to my dresser here in my bedroom with the TV on. (One of the fringe benefits of being divorced -- no more crazy nagging wife to put a complete stop to presence of motorcycles and motorcycle parts in the house. Until 2 months ago I had a 250 Bultaco Alpina in the bedroom -- that felt reeeal good now. Had it there fer 2 years, ahhhhh.....)

Anyways, here's how I used Mr. Bomb's advice: I got off my lazy ass and walked the 5 feet and grabbed the bank of carbs and went back and set down.

Then -- here's the tricky and weird-o-rama bit -- I pretended I was the motor and sucked air through the engine side of the carbs, whilst my finger was on one of them 3 nipples.

The test went like this:
- suck on carb mouth #4: no suction on nipple #4
- suck on carb mouth #3: FOUND IT MAN. Suction on nipple #3.
- suck on carb mouth #2: (had to make sure, it's late): no suction on nipple #2.

REPEAT THE ABOVE TESTS as I have impressed myself with my inspirational flash-o-genius in deciphering this tricky problem.

SHO' NUFF -- I was right in my hunch, that nipple on the #3 carb IS THE VACUUM LINE hookup.

The other 2 nipples on #2 and #4 carbs are just vents er sumthin'.

THANKS TO Y'ALL !!!!!

they be vents don't cap them off. i'd have waited until i got them back on the bike just in case somebody walked in on you, that would be a hard one to explain don't you think. but muuy good thinking on your part i must admit i wouldn't have thought to do that.

timebomb33 wrote:

they be vents don't cap them off. i'd have waited until i got them back on the bike just in case somebody walked in on you, that would be a hard one to explain don't you think. but muuy good thinking on your part i must admit i wouldn't have thought to do that.

Without your help there I'm going to sleep tonight worried about yet another 'gotcha' on me before I get this 12-years-setting-on-a-porch-outside bike running again. The more things like this I know are done correctly, the faster I'll narrow down the real problems I'm sure to have once the cleaned-up gas tank, carbs, fuel lines and vacuum line are back on the bike correctly. I've done a lot to this machine and I'm hoping it'll start and I want to thank you for the inspiration, and I now know what the residue of Berryman's carb cleaner tastes like, and well worth it to solve this mystery. Thanks!