650 Carb Question

I went to take apart the carbs on my 78 650 B2A and the main jets seem like they are really small. From what I have seen they should be 102.5 stock but mine were 90. I was wondering if anyone could let me know what the stock jets should be and also what position the needle clip should be in. The bike has the stock airbox and filter and stock exhaust.

102.5 was stock on most KZ650s, however looking at the parts fiche there was certain USA built KZ650s with carburetors that used 90 in the 78 B2A run, so your's may or may not be stock. Standard needle setting is in the 4th groove, one groove up from the bottom.

Alright...when I took it apart the needle was in the middle slot so I wasnt sure. I guess I will leave the 90 in there and see how it runs.

Does it matter that there is a small washer under the clip on the needle. When I took them apart the clip was in the middle but had a small plastic washer under it and I was wondering if this should be left there or removed.

From what I was told when I bought it the carbs were stock so I dont know why the clip would have been in the 3rd position if it is supposed to be in the 4th?

Also it the #50 jet that is in the same hole as the pilot jet the correct size?

What is the correct measurement for the height of the floats from the gasket surface, I cant seem to dinf this.

Thanks in advance for the help.

Post edited by: onuLine57, at: 2007/06/13 13:34

There were a bunch of main jets used in various VM24 assemblies... from #90 to #102.5. The carbs in 78 were the leanest plus used the limiting #50 jets that sit ON TOP of the pilot jets. You can actually put in #102.5 mains and won't run rich on top. The #90s are lean. The #50 jets can be removed and stored in a safe place... they serve no real purpose except to lean the #15 pilots below just a tad.

As far as your jet needles, the jet needle has 5 clip positions. Clip to the 4th slot. There should be a THIN plastic "washer" below and and thicker plastic "washer" above the e-clip. There should be a spring under there as well I think... the jet needle will go through it and it serves to tension the jet needle slightly so that it can ride up easily and bump the little round plate above that sits just under the actuator. The base of the actuator and plate are secured via two 3x12mm screws.

I thought the thir slot was stock adjustment and forht was leaning the fuel? Now I am confused.

Slots are numbered top to bottom with the #1 slot at the top. When you clip on the #3 slot, that is the middle slot. When you move the clip down to the 4th slot, that raises the jet needle. The needle will be relatively THINNER in relationship to the needle jet which is the hole it sits in. The thinner profile lets more gas by, richening the mixture. On most of the VM carbs, one slot position doesn't have a HUGE difference. The later 24s had smaller needle jets and so clipping the the 4th slot compensates for that little attempt at leaning out the carbs. Some documentation call for putting the clip on the 4th slot. The 77 VM24s were the easiest to deal with with a bit richer jetting and air screws. The 78s got lean and then came the pump carbs. Fortunately, the 24 pumpers work very well when jetted properly unlike the 26 pumpers or even the 28s.

Thanks for the help...any info on the float height. I read in the archive that is should be 25mm from the gasket surface with the gasket removed, is this correct?

Post edited by: onuLine57, at: 2007/06/13 20:38

I have said this a bunch of times but the float level measurement might have been useful 25 years ago before many sets of hands have done lots of bending on the floats but today, the floats have likely lost their original orientation and you had best use the service fuel level method to check the amount of fuel in the bowl. Hose held next to the level bowl will show the true fuel level and it should be 1/8" below the gasket mating line. Lots of threads in this forum with pics of this process.