vacuum problem?

hey guys, first post, first bike...here goes

I just bought an 81 KZ750(four cylinder); It would barely start when I bought it, but after a little work (new gas, oil, plugs, clean carbs) it runs. I live in S. California, so there isn't excessive rust/weathering on the bike.

It starts up and idles on full choke. This is where I run into problems: The bike runs ok on choke, and dies as soon as you even think about taking the choke off; apparently this means its lean.

When I was removing the carbs I noticed that one carb didn't have a vacuum hose attached, so without knowing where that vacuum hose goes, I capped it off and crossed my fingers that it wouldnt make the bike run too lean or rich. Now we've got 3 vacuum hoses attached: 2 are on a Y connector, and one goes to the pitcock...can I just cap them all off and then cap the pitcock port off as well?

I know that a manual will answer my 'where does it go to' question, but I'm still waiting on it.
I'm missing some fundamental aspect of these vacuum ports; I don't understand why its important to have vaccum hoses that lead to nowhere; I understand why you need the vacuum to the pitcock, but the other hoses don't seem to go anywhere special, so why even attach them?

Any help/speculation is appreciated...this is my first bike, and I just want to get it running so I can learn to ride already. Thanks

One line will be a vacuum line, and must run to the petcock as you've surmised.

The rest are probably overflow lines or vent tubes, especially if they go nowhere. As I understand it, the vent tubes provide outside air to the carb bowls (the bottom part of each carb), allowing fuel to be properly drawn into the jets. If you cap these off, the bike may not run correctly as a result.

Overflow lines are meant to direct fuel away from the hot engine, especially if the bike were to tip over. These are usually routed towards the swingarm, and away from the engine. If the bike were to slide, metal against the road could even spark, so these lines reduce the chance of fire should the bike be dropped.

There may be some emissions stuff that hopefully someone more experiences than myself can help you with.

Pictures are always helpful and appreciated if possible.

Welcome to the forum!

Chet... Let me chime in on this a bit... Anyway, welcome to the site asdfbeau... first thing I would very much appeciate is for you to go to your profile and find your signature and edit it to relfect your bike year/model and it always helps to have a location as there might be some kind soul who is willing to run over and lend a hand on site!

Second, each carburetor has a vacuum port; regardless of the type of carburetor. Your type of bike came with either Mikuni BS series or Keihin CV series carbs. The ports are located in similar locations on either type. They are directly above the venturi attached to your intake manifold. When the bike came from the factory, ONE vacuum port was capped. One vacuum port was attached to the petcock diaphragm via a hose. This port actuates the petcock and your bike will not draw gas otherwise unless you cap it and operate with the bike in "PRIME". If you do, set the petcock to ON or RUN (whichever it is labeled) when you want gas to SHUT OFF since you have disabled the vacuum actuated petcock. The other two ports have hoses that connect in a tee fitting. The other end of this fitting connects to a emissions device that is vacuum actuated. If the emissions device which looks like a brass colored cylinder about 4 inches long on most bikes, is gone, the hoses should be removed and vacuum caps placed over the vacuum ports on those carburetors. Any vacuum ports left uncapped create a major air leak that can hole a piston. I also suggest you look at the top of your valve cover if the emissions cannister is gone. there are two hoses up there that will not be connected to anything. These lead to ports in the cylinder head that are now not connected to anything. I would take the hoses off your valve cover and plug the holes in the valve cover with Permatex (black) so that air isn't sucked down into the combustion chamber through your reed valves which may or may not be in place inside the valve cover under the two covers on top the valve cover.

On the Keihin CV carbs, they are self venting. On the Mikuni, the vents are the pivoting tees between 1&2 and 3&4 carbs. Put a hose on each of these (if you have Mikuni BS carbs) and route the hose over your swingarm. In the event you tip the bike over, gas will spill out and it is better to wash your rear tire than to flow on your hot engine (fire danger).

thank you both for the reply and welcome (I'll make my signture more specific right away)
It came with Keihin CV carbs; they had a little rust in them, but after having cleaned them, the problem persists, hopefully my manual will come today, so I can try and troubleshoot other areas.

"The other end of this fitting connects to a emissions device that is vacuum actuated. If the emissions device which looks like a brass colored cylinder about 4 inches long on most bikes, is gone, the hoses should be removed and vacuum caps placed over the vacuum ports on those carburetors..."

I think that is the key part that I was missing. To me, it looked as though the hoses connected to another, larger hose, that emptied into the airbox. i.e. it looked like they went to nowhere
I'll double check all of my vacuum hoses/ports, cap them off if necessary and see how she feels then.
I've also seen a coupe of other threads with the same symptoms that I have, maybe one of their solutions will help me as well.
Thanks again, you guys have been a big help.

You'll get much use out of the Kawasaki site:
tinyurl.com/oza3y
and the diagrams found there, like these.
And you'll be able to tell a lot more with the shop manual or Clymers.

and...

Post edited by: bluegill, at: 2006/03/15 21:46

yeah my wife says i have a vacuam problem also,they scare the hell out of me!:whistle:

I am so glad we never had that emissions stuff up here. It looks like it could be prone to problems and confusion.

........................................................................................
Woodstock ON Canada
1980 kz750E1, 4->1, K&N pods