KZ650 Carb Synch and MORE...

Hey Guys, So this 80 KZ650 F1 I picked up has some carb issues and this would not be my best subject I have already learned a lot by looking around this forum and am hoping for some more help...

After the bike is warmed up it will idle but it does not sound quite right and will not idle down under 1300ish without stumbling. If I turn the air screws "IN" the idle increases... the other issue is it bogs hard about 5-6000 RPM. Reading the plugs was not much help for me as the base of the plugs are sooty black but the ground electrode is bright white :S

The bike came as I have found with stock exhaust, Chinese Pods, Martek 440 Electronic Ignition and Andrews coils.

I have a "Clymer," manual and followed their maintenance routine including a compression check (the specs are out in the garage but they were good), properly adjusted the valves (had to replace 3 of the shims) and have an assortment of pilot and main jets to play with. I did an initial cleaning and set the mechanical Synch. Now I am to the point of doing the "Fine Synch".

When I hook up the gauges to the manifold boots I only get about 6 vacuum inches. 1 was at 8 and I adjusted it down to meet the others. The Specs say 18 to 24 cmHG or basically you have a vacuum leak or need to clean the carbs.
I have done the spray around the boots and listen for change and get none. Since they are all in Synch but out of spec together is this a difference in "Vacuum Inches" and "cmHG"? I tried to Google a conversion but could not come up with one.

I have attached a couple pics, I suspect these are not the stock carbs as they dont have the "ribs". Could someone identify these and more importantly can someone like Patton (hint, hint) post an illustration of the ports so I know where to spray carb spray and where it should come out when I clean them again?

I intend to check the fuel level but these carbs dont have the "side" ports on the bottom of the bowls, just a large "cup". I am going to pick up a spare one and drill and tap a nipple onto it if I can find one but I suspect I need to figure out what the carbs are first to find an extra one to modify.

Plan of attack: Clean carbs again using hopefully supplied illustration, Set fuel level in each carb, Check what clip/needles are currently set to, check what pilot and main jets are currently installed so I can supply this additional information.

Sorry for the LONG post but I thought I would give as much info as possible up front.

Thanks in advance for your time, suggestions and help!!
Scott







Pretend the needles are pointing at 6 :silly:

I don't see what scale your gauges are. Vacuum can be measured as a column of water, or more typically a column of mercury (Hg). I assume your gauges use mercury. If the gauges actually use inches of water, then you have a vacuum problem for sure, but I doubt it.

Depending on the state of the motor, idle speed, etc., you will typically see 6 to 12 inches of vacuum. 6 is on the lower end, but I wouldn't worry about it.

To convert inches to cm, take the inch reading and multiply by 2.54.

Your 6 inch measurement is 15.24 cm.
8 inches would be 20.32 cm.

To go the other way, divide the cm reading by 2.54, which gives inches.

Here are some notes about manometers:
home.comcast.net/~loudgpz/GPZweb/Manomet.../ManometerNotes.html

I can't say for sure what they are, but those are definitely not stock 650 carbs (VM22s or VM24s). As you say the VM24s (and VM22s) have ribs - your carbs look a lot like a set of 29mm smoothbores, check here for pics.

As for the vacuum, 6 inches of mercury = 15.23 cmHg so that sounds about right - converter can be found here.
Also if you look at your gauges and compare the outer scale (inches) to the inner (mm) you'll see that a reading of 6 inches puts you close to 150 mm which is the same as 15 cm.

Btw, I couldn't tell from your post so pardon me if you already know, but vacuum synch should be done with the engine fully warmed up.

Edit: Dang Lou, you a Ninja??

My enter button is coil modded. :laugh:

Good eye on the carbs.
Do 29 Smoothbores fit on a 650?
Maybe some Suzuki carbs fit from that era?

Not to rub it in (too much) but just got back from a nice 200 mile ride on my Ducati Monster. Upper 70's to low 80's here on the Central Coast of California!

Now back tot the task at hand, thank you guys for the info. I susupected it had something to do with the scale of the gauges. I borrowed them and had no previous experience but given the couple of conversions you guys came up with it looks like I am in the ballpark vacuum wise!

thanks for the links guys, I will give all 3 of them a good read. I really appreciate the info! And yes OnkelB I read somewhere to be sure to have the bike fully warm when doing the fine Synch so that is what I had done. Thanks for the additional reminder though. When I get the carbs back apart again i will take some more pics in hopes of identifying them.

Scott

Additional Question if I may:

Vacuum lines, I have cyl. 1 and 4 intake boot line going to the Air Injector system. Number 2 intake boot line goes to the petcock vacuum. Number 3 is plugged. On the Carbs themselves only Numbers 2 and 4 have vacuum nipples. These lines are currently just hanging down (like where overflow lines would go) But I dont think these are overflow as I can feel very slight vacuum. Any idea where these SHOULD be going? Should I plug them, or plug them together? Or just leave hanging?

Thanks Again!!

DOH! Looks like I have the infamous 29MM Smoothbores. PerZ1E:

3 Phillips heads on the cover and The float bowl went back to using the 17mm drain plug directly under the main jet and none of the VM29's have an overflow pipe fitted in the float bowl.

That is me all the way! They cary the Fuel level gauge tool and the nylon choke rod pull I am missing. going to put those on order ASAP.

they also had this handy chart I can use as a sort of guide:

29mm smoothbores KZ650
Main Jet 105
Air Jet 0.9
Needle Jet O-4
Jet Needle 5DL31-3
Throttle valve (slide) 1.5mm cutaway
Pilot Jet 15
Air Screw setting 1 1/2 turns out

Could improvise fitting to 17mm drain hole by using a suitable rubber grommet or fuel line, in which to place a smaller clear tube.

Slight fuel leakage at the joint won't invalidate the test.

I use a cone shaped rubber grommet held against --- partially inside -- the drain hole and have no leakage during the test.








Don't forget to clean the small pilot air jet, which should be removable..





Good Fortune!

Just an update on my Carb tuning process. I prolly have 10 - 12 hours into carb tuning alone, good news I am getting GOOD at pulling the carbs LOL!

After re-cleaning the carbs and noting what jets and needle clip position I also did the float height check. I moved on to doing a successful Fine synch again.

I am at a point now where it idles well after changing out to smaller pilot jets and adjusting the air screws a bit.

I then moved onto the needle. I have actually moved the clips UP 2 positions, 1 position at a time and recheck. They are now in a good position as the plugs look good for idle to off-idle and it runs well in this range.

Next up, it bogs hard from half throttle up, although sometimes it comes to life in different areas/RPM's. I am going to start doing plug chops and figure out where I am with the Main jets. I thought all along it was running lean but so far the things I have changed were because it was actually too Rich.

Scott

Dumont wrote: Just an update on my Carb tuning process. I prolly have 10 - 12 hours into carb tuning alone, good news I am getting GOOD at pulling the carbs LOL!

After re-cleaning the carbs and noting what jets and needle clip position I also did the float height check. I moved on to doing a successful Fine synch again.

I am at a point now where it idles well after changing out to smaller pilot jets and adjusting the air screws a bit.

I then moved onto the needle. I have actually moved the clips UP 2 positions, 1 position at a time and recheck. They are now in a good position as the plugs look good for idle to off-idle and it runs well in this range.

Next up, it bogs hard from half throttle up, although sometimes it comes to life in different areas/RPM's. I am going to start doing plug chops and figure out where I am with the Main jets. I thought all along it was running lean but so far the things I have changed were because it was actually too Rich.

Scott

I had bogging issues just as you describe. It would bog out at full throttle and be choppy as RPMs rose towards 5-6K. It ended up that my Dyna ignition plate went bad. I suspect this was because the previous owner used the stock coils. I replaced the Dyna plate and the coils with 3 OHM Dynas, this fixed that problem... almost $300 later.

Further updates...

I ended up moving the needle up 1/2 more of a slot (moved it up to the top and then added a washer/shim) and picked up a pair of 105 and a pair of 107.5 main jets a sit was still Rich at the top. It was really confusing because everywhere else it was so LEAN. I got to thinking about these cheap chinese pods on this thing. I pulled them off and went for a quick trip and VOILA, the thing runs great everywhere now. So the PODS were actually restricting airflow. I was talking with my Uncle about this and he suggested "You should use velocity stacks with screens, and stay out of the dirt". So after much searching I found a set and ordered them this morning.

We''ll see in about a week how this all turns out...

Screens will keep the big stuff out, but not the fine road grit. That stuff will be mighty hard on your cylinders and piston rings. Ed