kz650 jets

hi all. opened up my vm22s carbs on my 78 kz650d1a sr. the bike has pods and a 4 into one Kerker from the late 70's.
found the carbs to have nylon 112.5 mains and something i haven't seen before a 15-pilot jet with a 50 jet over top of it.
the nylon jets were new for me and I've never seen a double jet pilot jet. first. anyone ever see this? and does this sound like a set up that should work with the pods and exhaust
the original owner who hadn't run it since 1984 told me it ran like a mother with this set up. and he put @ 5,000 miles on it before i just picked it up.
thanks

Plastic jets were a thing at one point, now discontinued as far as I know.  Regarding the double jet VM's, they were a thing also.  No clue about jetting, other than consider air correction jets to save trouble with rejeting.

what ar air correction jets? never heard of them.

Ive built and tuned dozens of 650's. 
firstly vm22's and a 50 jet over a 15 pilot are an american thing to try to comply with American emissions regs.
they were tuned so lean that a small reservoir of fuel was required between the two pilot circuit jets to prevent them from cutting out whilst off throttle  during gear change and coasting. 
To get the best from the engine find a set of vm24ss airscrew only carbs as fitted to the 650s the rest of the world got.
standard jetting for those is 15 pilot and 102.5 mains standard. With pods 15 pilots and 105 mains, or 107.5 max, then add air corrector jets to the pilot air intake port to cure the flat spot between pilot and needle jets at about 3k rpm. Zed1015 can supply the air correctors required. 
with vm24s and correct mixture setting, you'll gain about 10% bhp boost. 
Carburation affects performance far more than exhuast, unless its highly restrictive, so start there and that should cure the rich mixture your profile name suggests. 
also if not already fitted change to one grade hotter plugs as the early service bulliten advised. So ngk b7es or denso w22es. Also ensure you only have a max of one resistor per cylinder ignition line to prevent a weak spark which would also present as a rich mixture and give sooty plugs.

richmixture wrote:

what ar air correction jets? never heard of them.

www.kzrider.com/forum/23-for-sale/611992...lide-mikunis?start=0
 

thanks guys. man, i think i have a lot to learn.
fun stuff. i just cleaned and rebuilt with new brass jets.all the same as prior
I'm going to see what happens when i put some gas through it.
not thrilled with having to get different carbs.
but we'll see. it is good to know there's a way to get it right though.
much appreciated
 

warren. dont want to sound like a noob but i dont know what you mean by "make sure i only have one resistor per cylinder ignition.etc"
and if i change carbs and add correctors am i leaving out the #50 pilot? thanks in advance.                                   

Hi, Warren is referring to 1 resistor per cylinder, so either a resistor plug or a resistor cap or a resistor ht lead., and yes leave out the 50 jet . I think that the later carbs didn’t have the internal thread to be able to use the 50 jet anyway, but Warren will probably confirm that.
Rich.

One resistor per cylinder ignition line. Either resistor plug, resistor cap or resistor ht lead. Or better still no resistors at all.
You can leave the 50 jet out alltogether and just richen up the pilot circuit and keep using the vm22's but you will not get the power increase that 24's would give you.
you mentioned youve added NEW jets. If they are not genuine mikuni or keyster do not use them. Amazon/ebay/afternarket kit jets are the cause of 75% of the running issues i see.
Another thing to check is the quality of the pods you are using. If they have a lip that when fitted covers the pilot circuit air port you'll always struggle. 


For your set up i would start with checking the pods. Removing the 50 jet. Use 15 pilots.  105 mains. Airscrew 1.5 turns out / Fuel screw 0.75 turns out. Needle clip 4th slot down from top with air corrector jets fitted then colourtune the warm engine at 1800 rpm

With a 112.5 main your plugs will be black (rich)

thank you for all this awesome info. really helpful. cant wait to post this sucker running like a mother
im getting pumped.