1978 650B Can't keep it Running - Carb Help VM22SS

First post and I'd like to thank everyone for all their previous information because this place has been a wealth of information. This is my first foray into automotive so I'm learning, but I've always been able to figure out things pretty quickly.

I pulled a 1978 KZ650B out of my dads barn a few weeks back and have been tinkering with it ever since. He purchased it in 1996 with around 31K on the odometer and over the next two years put just shy of 2K on it. It always had charging problem (short rides) and my uncle always thought it ran a bit funny and figured carbs needed work. In 1998 the bike was stored improperly in a company warehouse and the only time it moved was when the company swapped locations. Needless to say nothing was drained or prepped for storage.

First thing I did was drain tank and change fluids. Carbs were torn down and rebuilt with new kits from Z1, first time and it was a bit rough here and there. Valve clearance was set with 4 trim nails on bench. New battery installed and I was well on my way to getting it running. I had some issues with rust in the tank so I used "electrolysis" to clean it up and I also had to pull my petcock apart after that fiasco. I went to get it started and it would turn over and run for about two seconds and die. I thought it was a bad ignition system or coils, but after some inspection and cleaning, they checked out fine.

I pulled carbs apart again and found I had tightened two of the pilot mixture screws too tightly and had popped the tips off into the carb body. Some time with a blowtorch and dental pick and they were back out and I went ahead and used the old pilot screws and tossed all 4 of the new ones. They seemed to be trouble.

Now that's where I stand. I pulled carbs apart 100% again and re-checked everything! All appears well. Put them back on tonight. Setup a fuel bottle with filter one it and plugged the vacuum tube for the petcock. Went to start the bike and like it has been doing it fires right up but stalls out with a few seconds. Typically it gets up to 1k RPM's and fades down to nothing. It's clearly getting fuel and although I know this I still have not checked floats (tool on order) to ensure that is not the issue.

Now this is where my lack of understanding perked up and I found something interesting. While on the bike if I rock it back and forth right after starting I can keep it running for quite some time, but it often spikes up to 4K RPM and then settles back down just above 1K. Almost runs away at times and I cut the motor to stop it from going any higher.

At this point I'm starting to feel a bit lost. Carbs were rebuilt using same jet sizes (90 main) as I found on the bike before and needle was set to third clip, again set to how it was before.

I know it's getting fuel and a check of the plugs (black soot) showed it was running rich although the fact it is stalling out leads my mind (again I dont know much about motors) to believe it is running lean and dying out from fuel starvation. All 4 pipes are hot so I know all cylinders are firing.

I guess I'm after conifrmation that checking the floats is a good idea, but I really don't understand why the rocking of the bike keeps it running? What else could I possibly be missing? It clearly turns over and wants to run, but I can't seem to understand the fuel issue.

Thank for any help or direction.

Welcome aboard! When you start the bike do you have the choke on? Usually some choke is needed to start the bike and then it can be gradually turned off as the bike warms up. Here's some general info you may also find useful. Ed

kzrider.com/forum/10-new-members/589649-...r-savannah-ga#594587

Choke is fully on, if I try to lower it, the motor stalls. Plugs 2,3,4 are completely black (brand new) and #1 looked good. I tried to match synch everything similarly on the bench to get a good match.

Shot of the bike.

A few questions....

It appears that the mufflers are not the stock parts. Does the bike have the stock air box and air filter? If not, what has been done to the carbs regarding rejetting? Also, assuming the carbs in your photo are the ones that originally came on the the bike it is a KZ650-B2A rather than a KZ650-B2. The distinction there is that the carbs are not the normal VM24SS (24mm) models. Instead, they are VM22SS (22mm) carbs. That may be worth noting when and if you must rejet them. The easy way to identify the 22mm carbs is by the extra orifice on the throat (see arrow in pic). The 24mm carbs do not have that. Ed

Sadly I have seen you post that before and completely took it backwards. I do have the VM22SS, would probably explain why every search always seemed to be the wrong carbs. :S Two weeks of thinking that... I just figured there wasn't much info. Yes it would probably appear that I do have the B2A, I had wondered that early on, but it seemed very consistent to the B model and I didn't think much beyond that.

Also I know nothing about the original owner of the bike, so exhaust could be aftermarket, but it is what was on the bike in 1996.

Air box is stock, with K&N washable filter.

Looks like I'll go back and start looking for info on the 22's and not the 24's. Thank you!

If the bike only runs on choke then your carbs are still dirty and clogged. You will have to do a thorough cleaning making sure to clear out the idle circuits int he carb body not just the pilot jets. Make sure every circuit in the carb bodies are clear and you can spray cleaner though all of them. It is a time consuming task to clean the carbs and requires patience so take your time. The reason it will keep running when you rock it back and forth is because you are splashing fuel into the intake track from the float bowl so it will stay running.

Carbs were and had be cleaned more times that I could have imagined. I had purchased 4 new carbs kits that were more specifically for the 24's , but seemed to be good for the 22's per website purchased from. Well I think that is not quite the case because it wouldn't run with all the new parts, but as I put the old stuff back in it began to come to life. All said and done, I think the biggest issue was the with the float. The new float needle seemed to sit a bit taller in its seat and I think that in turn lowered the height the fuel would fill the bowls.

I also went back to the original needle and pilot screws. On the pilot screws I shaved off the limiter stop because to adjust it was almost impossible you. You had to fit a small screwdriver underneath the bowl to make any adjustment over 1/4 of a turn. Typically it mean I had to pull the carbs off to make that adjustment because I just struggled to get a screw bit in there.

It's not 100% by any means, but I was able to get it running and idling without the choke on. I do have few leaks in the inlet boots, so I'm going to have to figure that out and I'm not getting much heat on header #3. Again, it's early, and more importantly its alive!


Hopefully a few hours on it tonight and I will atleast get to take it for a spin around the neighborhood.

Since the carb holders are leaking I would correct that before making any other changes. The effect leaky carb holders can have on the bike's ability to idle is remarkable. Ed