carb id

i'm still having carb trouble. can someone look at this pic and tell me what carbs these are. the tital says the bike is a 1978 kz650..the sticker between the forks says 06/78..on the motor it is stamped kz650b1. i order some carb kits and put them in and i have way too rich. the jet needle that came with the kits are #y63. i have a haynes manuel and it says the jet needle should be #5dl 31. where can i get just the jet needles.any help i would appreciate..mustache

Post edited by: mustache, at: 2006/05/20 19:07

You have VM24SS carbs there.

My Factory Service Manual states the Jet Needle as 5CL16-3.

thanks for the reply..what does your manuel say for the main jet..thanks again

where can i buy jet needles.need some bad.i looked at z1interprises but didn't find the right number..thanks for any help..mustache

Main jet 97.5.



Post edited by: rstnick, at: 2006/05/21 13:30

The Y63 jet needles are badged by Keyster I believe and are direct replacements for the Mikuni 5DL31 jet needles. The Y63 jet needles work fine as they replicate the taper and length faithfully. The 5DL31 jet needles have a better profile than do the later 5CL10 or 5CL16 for all around riding as those jet needles are more appropriate for a leaner air/fuel mix although shorter to allow the bike to come on main jet sooner. They were put in for emissions purposes and if memory serves, used with different holders. The 5DL31 jet needles just had an eclip and dropped under the slide mechanism where the 5CL jet needles may have fit into a spring loaded recess and had plastic spacers and a metal keeper above it. I see so many darn carburetors, those details blur but that is my recollection.

The #97.5 main jet versions of the VM24 have a #50 jet OVER the pilot jet (#15) in most cases and these are about the leanest of all the VM24 variations. They perform a bit better with a bit richer jetting even with a stock airbox. I start them as a #102.5 base for main jet and up the main jet if pods are used. The #15 pilots work OK but if there are pods or pipes, #17.5 pilots work better. Reclipping to the 4th slot doesn't hurt performance a bit even with a stock airbox.

thanks wiredgeorge for the reply.
when i built these carbs the main jet was a 90 and i put 90 back in. the pilot jet is 15 with 50 over it. the jet needles i cant say what they were because it seems i lost them. they are completely gone.
i can put new plugs in and it runs great all ranges but after a few miles the plugs fowl out.wet and black suit. i did the coil relay deal and it helped just a little bit just a few more miles then fowl out. i am at a loss now if u say the y63 jet needles should work..wouldn't a 90 main jet make it run leaner than 97.5 ?..does pods make it run richer or leaner?.i am really at a loss...thanks for any help u give...mustache
ps..before i built the carbs it didn't run rich just didn't run good

Post edited by: mustache, at: 2006/05/22 21:48

OK... now we are getting somewhere... the plugs are fouling? You did the coil mod? First, most plug fouling due to carbs is cause by the pilot circuit or mid-range. The main jets meter gas ONLY when the bike has a wide open throttle so I would guess you are not running around on wide open throttle when the plugs foul. Since the puny #15 pilot jets (stock) are not likely to be the culprit, and you can't get any smaller pilots, I would adjust the idle mixture for the highest idle speed using either the air jets or pilot mixture screw (on bowl bottom). I don't know which your bike has. Once you have the highest idle, turn the idle speed down using the idle knob. If that doesn't fix the problem, then you have narrowed it down to the aftermarket jet needles.

The Y63 jet needles are replacement for the 5DL31 jet needles and you didn't hve 5DL31 jet needles. You had 5CL10 or 5CN16 or something like that. These were matched to your needle jet which is the brass doo-hickey sticking out of the bottom of your carb's venturi. If you have done the coil mod, I would say that the Y63 jet needles are your problem... You or someone swapped in the carb kit jet needles and these are thinner and longer than the ones they replaced.

To try and fix the problem using those aftermarket jet needles, try lowering them two clips from where they are now... IF you clipped them at the fourth slot, clip them at the #2 slot counting clip positions from the top. This will LOWER those jet needles and a wider spot will occupy the needle jet at almost all throttle positions, letting less gas through. You will need to resync the carbs again when done.

wiredgeorge thanks a bunch
i will try different slots on the clips..i was thinking that that might be my problem..i have every piece of the old parts out of those carbs except the jet needles. they just disappeared. i am having a little surgert thursday so i will let u know later when i can work on them again..once again thanks to u and all who has helped...mustache

well i've pretty much recoverd after my little bit of surgery..any way i did what wiredgeorge said move the e clip up two slots but while i was doing that i noticed on the slide throatles one is a different size. three of them are a 2.0 one is a 1.5...do i need to find another 2.0 or how much difference will this make.
thanks for any help..mustache.....mabe i should just try and find more carbs..LOL

one of the previous owners has really done some screwing with these carbs. one throttle valve is a 1.5 and the other three are 2.0..i bought another set of carbs for parts and all four of those are 1.5 [just my luck]...my question is would i be better to use those 1.5..if now where in the world can i find another 2.0.
thanks for any help..mustache

The slide cut out controls air flow to a large degree at lower engine speeds. If the slide cut outs are different, you will never tune the carbs properly. Sorry...