78 650' Carb issue. Broken needle stuck.

Personally I'd get A set of 24s without the accelerator pump ....might be cheaper to rebuild and work just as good.

Yeah I was just looking at wg's site, Im trying to do a bit of research on pump vs no pump on the vm24's any input for the 650? From what I have read it would seem no pump would be best.

The carbs on my 1977 KZ650-C1 have no pump and they have always worked great for me. I've owned the bike since it was new - April, 1977 (egads, that's 40 years!) It is my understanding that the KZ650 models first began using the carbs with the pumps in 1979, so the 1978 KZ650-B2 would not have had the pump. One thing to consider - the 1977 KZ650 models used manual petcocks as opposed to the vacuum operated petcocks on the 1978 and later models. Consequently, the VM24SS carbs for the 1977 models do not have the vacuum port on the top of #2 carb that is used by later models to operate the vacuum petcocks. So, if you buy a set of 1977 VM24SS carbs you may want to switch to a manual petcock (personally, I like them better since they are less prone to failure). If you buy a set of 1978 VM24SS carbs the vacuum petcock line will attach to the vacuum ports on top toward the front end of the #2 carb. Ed

Before you waste your money try to remove the stuck pilot screw needles.
Found at BikeCliff's Website.



Michael

But it was just the tip, and it was only for a moment...

What Ed said is correct and is good advice, and you'll like the bigger carbs. But I also agree you may as well try to extract the broken needle tips. I would try to use something that's not going to score or damage the surrounding aluminum or the hole itself. My chemistry knowledge is sorely lacking in this regard, but maybe someone else on here knows: Is there a liquid chemical that will dissolve brass but leave aluminum unmolested (and wouldn't be illegal or unreasonably dangerous to possess and handle)? If so, maybe you could get some, drip it into the threaded needle hole (with the carbs upside down), and let it soak until the brass tip comes out - sort of like using an alum solution (or whatever it is) to dissolve a broken tap. If not, I'd try to push out the pieces with the tip of an aluminum nail/screw or a piece of hard plastic - turn it to a point using a hand drill and some sandpaper if you don't have a lathe. It looks like too tight of a fit, but maybe a pair of micro needle nose pliers, like for small electronics work, would be able to reach into the hole and grab the broken piece, or could be ground-down to do so?

While we're on the subject of carb needles: I've overhauled a variety of Mikuni and Keihin carbs - sometimes installing new manufacturer needles, sometimes needles from K&L rebuild kits - and in the process, I've noticed that the taper of the tip of the replacement needles varied widely from the taper on the tip of the original needles. What's more, I never found the performance was affected to any noticeable degree. Sure, the exact number of turns-in needed for a good idle mixture might have been different, but that was it. This makes me wonder: Could the hole for the needle tip suffer some small amount of concentric damage (swaging or the like) - such as if a steel tool were pressed into it to eject broken-off needle tips - and still work fine? Seems to me it's possible, and thus it's worth a try to get out those tips. If for no other reason than you could then sell the carbs to help finance the replacement set.

I agree with everything being said, and I may do just that (The more carbs the better?) I would like to salvage the carbs I have now and get some new needles for them, then maybe try again in the attempt. But at the same time I think It would be nice to have both an air and fuel screw, and a little more horsepower from the larger carbs. Only time and money will tell!

For prosperity sake! I managed to fix my carb issues by bench grinding down a tent post in order to fix the problem.

Congratulation, good work
Another lucky member.

Right on - that's great! Sometimes the most effective tools are the ones you devise yourself, albeit with design assistance from Necessity (aka, Invention's mother).

Scirocco wrote: Before you waste your money try to remove the stuck pilot screw needles.
Found at BikeCliff's Website.

Michael

Yup, that tutorial is from The GS Resources. Cliff's website has compiled a bunch of those gems.

Mikuni liked to use paint on the threads of those pilot fuel screws which makes the screw hard to turn. Because of that it's impossible to tell when the screw is "lightly seated" thus a lot of guys turn in the screw too tight and bust off the tips. Pushing the tip backwards using an awl solves the issue though. It helps to custom grind the tip into a sharp point.

There is no reason to replace those carbs. You may notice that the hole is slightly larger when done though. Only thing that does is allow the pilot screw to poke out of the hole in the carb body a little further. No big deal.

The only reason I really would replace them is if they do not play nice with the pod filters. Otherwise the loss in horsepower and performance is minor in my case due to the fact its my first bike and I'm looking for it to run first before worrying about getting every little bit of power out of it.

Pods totally mess up the mixture. Serious rejetting will be needed. And the VM family of carbs are the easiest type to rejet.