TOPIC:

Hello all, 
I’m a long time member, but haven’t been active for many years. I’ve finally got back to my project which is a 79 kz650B. It’s starting and running, but my issue is...after accelerating   into 4th and 5th gear as soon as I let off the throttle it sputters and  ultimately dies a couple of seconds later. Almost like it runs out of fuel or oppositely gets completely flooded. 
The plugs look like I might be running a little rich but nothing crazy. 
I know y’all need a lot more info. So basically, I have pods and have it jetted accordingly. I’ve tried different needle levels and have found that the second clip seems to work best. I have adjusted float bowl levels with the clear tube method. Basically I have had the carbs off maybe 20 times trying to get this thing right. So many times that I’m starting to think it might not be the carburetors after all.
 My question is, what could cause this issue of the stalling with downshifting from 4th or 5th gear? Other that the carbs? Can I be looking a a timing issue? I mean, that’s what I’m leaning toward now. Because I’ve dialed the carbs in as much a possible. Although it could be the acceleration pump as I didn’t rebuild that yet... I have the kit to do it. 

Any other ideas y’all can give me would be greatly appreciated. My arms Are so sore from pushing carbs back into the manifold boots!!! But I’ve become pretty fast at taking them off!!!

 Thanks in advance, Matthew 

It could be fuel starvation. The strainer in the tank or the petcock or the fuel line itself could be clogged, letting only a little fuel through.
If yours has the manual valve, it is easy to test. Turn the fuel valve to OFF. remove the fuel line to the carbs. Peek into it. If it is clogged, toss it and get a new one. If it is not clogged. Put a longer piece of fuel line on the valve and stick the other end of the hose in a fairly large container, preferably a clear one. Open the valve and see how well the fuel flows. Also note if there is any sediment, mud, rocks, or dead pterodactyls in the fuel.

You can do a similar test with a vacuum valve, but you will need to apply vacuum to the valve with a Mityvac or some such, or just test it on PRI and hope that the rest of it is ok.

There is also a chance that the fuel tank cap vent is clogged, creating a vacuum in the tank. To test this theory, leave the cap open and take a ride. This is much less fun if the tank is full or nearly so, as the fuel will slosh all over you and the bike. It could result in a fairly spectacular fireball. The neighbors will retell the story for generations.

LOL!

Lots of things to check....compression first, then valve clearance, then coil voltage and resistance, then timing.  Eliminate all of the possibilities and whatever is left is your likely cause.

wrote:

It could result in a fairly spectacular fireball. The neighbors will retell the story for generations.

Remember that time in band camp!

Thanks for the response. Today I just replaced the old fuel petcock with a brand new one. So I can eliminate that issue now. I did put back in the old pilot jets just to see if that helps the issue. I have tried the fuel cap open thing and didn’t notice any difference. 
      I rebuilt both parts of the acceleration pump. Both diaphragms and springs. My rebuild kit had one ball bearing and 10mm long brass pin of some sort. When I took the old ones apart I saw neither of these . Do any of you know what those are for. I have vm24s and the exploded drawing in the manual doesn’t show these parts. Maybe it’s for a different year? Any idea’s? 

Yeah I know. I will be getting to all that very soon. I just don’t know when to quit looking for the culprit in carburetors. That’s my problem. I’d love to move on to valve clearances anything else but these carbs

I agree with most of what has been posted to this point, but would ask what jetting you ending up with with the pods.  You indicate you have jetted according.  Just what have you ended up with?   If is is a 79 and was a US bike then it has and accelerator pump and was jetting rather lean. As I understand it , it would of have a 97.5 main, a 15 pilot  and a 5CL15-3 jet needle with a AO5 needle jet. Not the leanest combo of any of the (K)Z650s but one of the leaner ones. 

Have you read any of the posts about the air jets (from zed1015 i think it is 1015 it is on other forums) and how there are solutions to adding pods?  The stuff we call gas now is not what it was when the bike was new. This is not paid the amount of attention that needs to be, it just is not what the bike was made to run on. So things need to be addressed.  .

Have any other things been change from stock ( different exhaust, increase in displacement , different cams????   

I have pods and 4 into 1 exhaust. My main jet is 117.5, I went down to the 101.5 stock jet and it was quite a noticeable difference. The bike had no where near the power and acceleration as the 117.5 main. I know that sounds like quite a big jump in size. But I’m using the Dyno jet kit. And this is the smallest main jet size they offer. From what I’ve noticed, the main jet is quite a good size, unless it’s leading to my current issue. But it accelerates and runs great until I let off the throttle, then it stalls out. 

wrote:

wrote:

It could result in a fairly spectacular fireball. The neighbors will retell the story for generations.

Remember that time in band camp!

BWAHAHAHA! I have no memory of band camp at all............

By kzed:  ....  I rebuilt both parts of the acceleration pump. Both diaphragms and springs.  My rebuild kit had one ball bearing and 10mm long brass pin of some sort. When I took the old ones apart I saw neither of these . Do any of you know what those are for. I have vm24s and the exploded drawing in the manual doesn’t show these parts. Maybe it’s for a different year? Any idea’s? 

The little parts (rod, ball & clip) should be fitted into the float bowl (see link below) & the o-ring goes on the pump nozzle. 
Each carb should have the 4 little parts.   The ball, weight & clip act as a one way check valve. 
When the throttle is twisted vigorously the pump diaphragm is actuated and fuel should squirt out of the nozzles & sraight thru the carburetor without hitting the carb bore walls.  If it doesn't or just dribbles out, the nozzles or something are clogged.  www.partzilla.com/catalog/kawasaki/motor...erator-pump-kz650-b3

Ok I have an update. I changed the jet needle clip to the 3rd setting, did a proper check to make sure the acceleration pump was working correctly and it was. And I did a proper carb sync with vacuum gauges, the bench sync wasn’t enough. Out of all those things done today, I think the vacuum sync made the difference. So far, the bike hasn’t stalled out on me after accelerating!!! I haven’t gone for a long ride yet but around the block it’s working. I let it idle quite a while after riding around and I’m idling good around 1000 rpms.       Lesson for this experience is don’t really on a bench sync!!!!    Thank you all for the help