TOPIC:

I finally finished up my 1979 KZ400H yesterday, and with the addition of a new seat I took her out on the road today for a shakedown. I never go far initially because as we all know, gremlins pop up at the most inopportune times, and today was no exception, although to be honest I was expecting it.

I'm pretty sure I know what it is, but I wanted to submit it to you guys for opinions - I'll put some gas into the carb via the rebuilt petcock and the new diaphragm I put in there, and the bike starts, and runs strong, too. I take her down the driveway, turn onto the street and accelerate, shifting through the gears and everything is fine...get about a quarter mile down the road (where I usually turn around anyway) and she starts bucking and stalling.  WANTS to start, but doesn't...I'm thinking floats here - maybe the float valve.  

I get her home, pushing her up the driveway (always Fun - it makes me feel my incipient heart attack waiting to happen), and drain the bowls. There IS gas, but not as much as there should be, I'm thinking...so I seal them up, put them on PRI and wait, and she starts right up, runs strong, etc.  This is why I'm thinking either floats or float valve.   Another interesting thing is, the Left carb drips out through the overflow - not steadily, but more like the float is letting in gas, which in turn fills up and goes down the overflow tube...the Right carb does not do this.

When I rebuilt the carbs, I replaced all the jets with new ones, but I don't think I took out the float valve; on my KZ400, (same as a 440??) I don't think I took it out, because it doesn't show it on the parts diagram, so I may have assumed it was part of the carb body - but what could be causing my problem? I'm thinking either sticky floats or sticky float valve - but what do You think??

Here's a pic, btw - - 
  

I had a very similar situation.

Long story short... the aftermarket vacuum / diaphragm petcock would only flow enough gas when idling... 
As soon as the throttle was opened, even a little, the vacuum dropped and shut off fuel flow. I tried TWO new petcocks, same result.
On "Pri" (prime) fuel flow was adequate though.

I even tried "T" connecting all 4 vacuum ports together into one pipe, to the vacuum diaphragm... same problem.
I tried putting a weaker spring behind the diaphragm... still didn't work.

The original Kawasaki vacuum petcock must somehow have a tolerance for a much lower vacuum. 

I have reverted to a manual (ON / OFF / RES ) aftermarket petcock.
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H.

A float valve consists of a valve body, and a needle.  In the case of those Keihin CV carbs, the valve body can't be removed from the carb body.  You can polish the bore though.  A Q-tip and brass polish works well.

Float height is just an approximation, in order to get the FUEL LEVEL to the correct height.  Your Kawasaki service manual should specify a fuel level, and show how to measure such using a piece of clear tubing attached to your overflow nipple.  You should go through that exercise as specified in the manual.  

One other reason some carbs seem to drip out of the overflow tubes all the time is when the tubes themselves crack.  It's not overly hard to replace a cracked tube.  I've written up posts on the details, or use google.  The Honda guys use a lot of Keihin carbs, so they are well familiar with the replacement process.  That's how I learned.

 

H - where did you get your non-vacuum petcock? I was thinking about doing that too when I was rebuilding, but I like to see if the OEM vacuum-type works before making the switch. Nine times out of ten though I go back to the manual type, they're more reliable. Just off-hand, do you know what the distance between the holes is? 

Ed, I'll pull the carbs tomorrow and clear-tube them, as well as polish the float valves, see what I get. I have a setup here I put my carbs on after I redo them and use alcohol to see what's what, it's a lot safer than gas when setting the float height. Thanks for the diagram too!

Just had a thought, though - if I use a non-vacuum petcock, I need to block off the vacuum nipple in the carb too, yes...?

Dr. Frankenstein wrote:

Just had a thought, though - if I use a non-vacuum petcock, I need to block off the vacuum nipple in the carb too, yes...?

yes

If you want to check the petcock I might suggest you set it to prime and see if it runs better or not. You are correct in that any vacuum port not connected to a device it is supposed to run should be capped/plugged etc.
 

I buy a LOT of bits for my old ladies from an on-line catalog: Moto Ward (UK based)
Predominantly Yamaha parts but many for older Kawasakis.

They are represented in South Africa by a company called StartLine, and they have a store less than 5 miles from me!

H.