kz650 Jetting

I have a 77' kz650 and it has a 720 kit with andrews .350 lift cams and pod filters with a Vance and Hines 4 into 1 header with no baffle. It runs amazingly. But, up top at WOT when i shift it tends to blow out fire and just have that lean burn smell. This is coming from someone who really knows what they are talking about, but he is a car guy and has no real knowledge about specifically jetting my application. So i went and removed the carbs and found 102.5 main jets. I tried some 105 jets and now at WOT it likes to stumble, so i went back down to 102.5 for now, but i would like to know what i should do? i am a huge car guy and i am mechanically inclined i just havent ever really messed with inline 4 carbs, but i dont need baby steps i can figure it out. Are the 102.5 jets just fine? or should i try something else. Thanks in advance and any help is appreciated.

Hmm, I´m by no means a carb guru (to put it mildly), but 102.5 mains is the stock setup for the 77 650 with stock airbox and 4in2. With a 720 kit, pods and 4in1 I´d think you are running lean at wot - off the top of my head and after a few beers I´d think you would need mains in the 110 - 115 range.

Post edited by: OnkelB, at: 2007/12/13 16:41

thanks for the reply, i have some 120's laying around do you think that it would hurt to try those? when i put the 105's in it still ran great and felt the same it just kept intermittently (sp?) cutting out at WOT so i thought that maybe it was getting too much fuel.

120's may be a tad much (no guru here either) but try it and check your plugs.

ok. thanks, another question is there anything else at all that i should change when i change the jetting? it seems like a pretty big jump from 102.5 to 112 or so, do i need to readjust the idle or anything, or just put the jets in.

Post edited by: kzdev1360, at: 2007/12/13 18:29

any time you change jets or anything on the carbs you should re sync them in,
have you checked to make sure your timing and valves are set,

what do the plugs look like?

also check the charging system and the power to the coils.
you may have already done all this, but I was just thinking to check the basic stuff also

I made my own rectifier over the summer when the stock piece went out and it has been great ever since, power to the coils is fine, timing is right on. I have not ran at WOT then killed it and pulled the lugs like i should but when iremove them after normal riding they are a good color of tan with the top two thread rings black. So they appear in great condition in that respect.

Post edited by: kzdev1360, at: 2007/12/13 19:54

Ron wrote, "any time you change jets or anything on the carbs you should re sync them in,"

Ron, I wouldn't think changing jets would get the carbs out of sync. If your pilot mixture is badly out of whack, and you tuned the pilot mixture properly, that can change the vacuum levels in the cylinder a tad but I doubt the jet needle and main jets being changed would affect sync. Do you have experience otherwise? Please explain, as I am interested.

On the jetting for this bike, the #120s will be on the the too-large side but #102.5 is definitely too small... I would think that the #112 main jets would be about right, reclip jet needles to 4th slot (now you need to re-sync as you will have to remove the carb sync actuators from their common rod) and use #17.5 pilot jets. These jets/settings should be about right. Start with your mix screws at about 1.5 turns out from lightly seated and adjust each in turn for max idle speed... turning the idle down between adjustments of each carb.

wow...thank you tremendously

is that the fourth line from the top or fourth line from the bottom on the needles?

damn this thing is fast...i never knew it could run this good. thanks alot guys.

Slots on a jet needle are counted from top to bottom... first slot on top is #1... when you seen 5DL31-3, that means 5DL31 jet needle clipped to 3rd slot as counting top to bottom (there are 5 slots total on Mikuni jet needles).