81 kz650 csr carb questions

Hello most helpful motorcycle forum on the web. After a brief hiatus i'm back on my pair of 81 kz650 projects! Both bikes are rough but running, now i need your help to solve a couple simple carb riddles. Note that the 81s do not have the round top carburetors.

Question 1: There is a vacuum port on carbs 2 and 4. On one of my bikes a vacuum hose simply runs from carb
2-->4, the other has open hoses from carb 2 and carb 4. Which is the proper configuration?

Question 2: There are small parts in each carb that i can best describe as a rod and a bb, held in place by an incredibly small c-clip. each carb is missing 2 of these small c-clips. The c-clips cannot be purchased anywhere without buying full rebuild kits (which i am not installing at this time). My question is, can i leave the c-clips absent or will thie negatively affect the running of the carbs? I assume the c-clips only function is to keep the rod and bb from falling into the bowl when removed. I hope someone knows what i'm babbling about here

Question 3: One of the kz's has a faulty vacuum petcock. When the bike isn't running if pours gas through the overflows, when the bike is running there is no leaking (hence a petcock issue and not sticky floats). The previous owner installed 2 inline on/off petcocks. One for the fuel line, and one for the vacuum line. My question is, does it require both inline petcocks, or can i remove the vacuum line petcock and only use the inline fuel line petcock until i replace the unit? I know i can just buy, but i w a manual petcockant to make this work temporarily while i'm doing my tuning.

thanks in advance for any insight. I've added a picture of a set of kz carbs i found on this forum for reference, they may not be from an 81 but are the same style and have the same vacuum ports as my carbs.

I have the same bike.

#1). Each vent port should have vent tubing which should be open to atmosphere.
Stock, each vent tube is routed over the airbox shoulders & fitted snugly between the airbox & side covers. The left side has a tubing/frame clamp

#2). Those little parts are for the accelerator pump: ball, weight (rod), clip. The K&L AP kit includes the little parts (Z1Enterprises.com). I do not know if the clips are absolutely necessary. It may hold the ball & weight in place when the fuel squirts - without the clips, maybe the fuel won't squirt out the nozzles correctly? Check by supplying fuel to the carbs, priming the AP circuit by actuating the throttle pulley, then actuate the throttle pulley vigorously: fuel should squirt out the nozzles without hitting the carb bore walls.

#3). You can probably rebuild the petcock & get rid of the extra add-on stuff. I would disassemble & clean the petcock & inspect it. PineSol & hot water & a toothbrush. Check the mating surfaces for pitting or scratches or whatever, especially where the diaphragm o-ring contacts the petcock body. Get a K&L rebuild kit - either a complete kit or just the diaphragm assy kit (Z1Enterprises.com). If you prefer oem, I believe the dealer has the rebuild parts.

firechicken wrote: .................
Question 3: One of the kz's has a faulty vacuum petcock. When the bike isn't running if pours gas through the overflows, when the bike is running there is no leaking (hence a petcock issue and not sticky floats). ......

First, I would not automatically rule out faulty floats as they may or may not be a problem. Fuel overflowing through the carb overflows must get into the carbs from the fuel tank. Normally this fuel comes from the tank through the float valves into the bowls. In your case, it is possible that fuel is coming into the carbs through the vacuum line on the petcock rather than through the float valves. I would try this: Disconnect the vacuum line from the carbs and hold it over a catch can. Regardless of the position of the petcock handle, no fuel should flow through the vacuum line. If it does, rebuild or replace the petcock. If no fuel flows through the vacuum line then one or more of the following is causing the overflow condition:

Remember - NO SMOKING or other activities that could ignite the fuel while working on carbs!

The float valve is not sealing. This may be (and probably is) just a matter of some minor dirt in the float valve and is very simple to remedy and can be done with the carbs still on the bike. Turn off fuel; drain carb by loosening big brass screw near bottom; and remove the 4 little screws on the bottom of the carb bowl. This will enable you to remove the carb bowl. You will then see the float. If you carefully remove the float you will see a stubby little needle that mates with a brass orifice; together, these two pieces are the float valve. Assuming there is no obvious damage to the needle or seat, use a Q-tip and some carb cleaner to clean the seat of the orifice and the needle. Be careful not to bend the tang that is attached to the float. This tang is the piece that the bottom of the float valve needle rests upon, and it determines the fuel level in the bowl, so bending it will change the fuel level. With the float valve cleaned it should no longer leak. To prevent a re-occurrence a quality inline fuel filter should be installed between the fuel tank and carbs. If there was damage the needle and seat should be replaced as a set; they are available.

The brass overflow tube inside the carb bowl is damaged. When you remove the carb bowl you will see a brass tube attached inside and rising toward the top of the bowl. This is the overflow tube and it leads directly to the overflow nipple on the bottom of the carb. Normally, the fuel level within the bowl rises somewhat close to the top of this tube. If the tube becomes cracked or separates from the bottom of the carb bowl fuel will flow through it and out through the overflow hose. Checking the condition of the tube is very easy after you have removed the carb bowl from the carb. Simply hold the bowl level and fill it up near the top of the tube with water or alcohol and see if it leaks. A slight crack in the brass overflow tube can be difficult to find. You can connect a rubber tube to the overflow nipple, fill the bowl with water, put finger over the open end of the brass overflow tube and blow in the rubber end and look for bubbles. If it does the best remedy is to replace it although some folks have found creative ways to repair them.

The fuel level is set too high. This condition occurs when someone has bent the float tang as mentioned above. This condition can be checked using what is referred to as the "clear tube test." The test involves attaching one end of a clear piece of flexible tubing to the carb drain hole and holding the other end of the tube above the bowl/carb joint. When the fuel is turned on it should rise in the tube to a level 2.5 - 4.5 mm below the bowl/carb joint. If the fuel rises higher than that level it may run into the cylinders or over the upper end of the brass overflow inside the carb bowl (mentioned above) in which case it will run out the overflow hose. This condition is corrected by removing the float and gently bending the tang to raise the float valve needle position. Doing this may take several tries before achieving the desired fuel level.

Correcting each of these three conditions involves removing the carb bowl. This task can be made easier if a short screwdriver bit is used, and depending on which carb you are fixing a mirror may help you locate the screws on the bottom of the carb bowl. Also, it is not a bad idea to have a new carb bowl gasket available in case the old gasket is damaged while removing the carb bowl. Ed

thank you for the replies, both have been very helpful. I have disassembled and thoroughly cleaned the petcock with no luck, the rubber gasket looked solid. I will test it and see if it is leaking from the vacuum line. I have cleaned the carbs and the thoroughly cleaned the float valve, The floats appear to be in good condition and are not bent irregularly (compared to my other kz floats). also, it leaks gas from every overflow, making me think it isn't an overflow tube problem. Also, i just installed fresh bowl gaskets so i should be good there.

As for question 2, I know that without the clip the weight will sit directly on the hole in the bowl directly under the check valve, I don't understand how the mechanism works so I also am unsure if it would block the flow of fuel. Martin, how can I tell if the fuel is being squirted through the "nozzles"? also, by nozzles what are you referring to? is it a specific jet? if so where is it located?

#3). The petcock has a round gasket w holes on the lever side & it should have a square diaphragm on the opposite side. The diaphragm can look good but be bad - mine appeared perfect to the eye, but it leaked fuel.

Disconnect the fuel line from the carbs, then direct it to a clear juice container using a long section of tubing to see if it leaks. manual valves removed & Vacuum petcock set to ON.

#2). The pump nozzles project into the carb bore on the airbox side of the carburetors (see photo). When the bowls are removed, you can see the base of the nozzles on the underside of the carb bodies - there should be a small o-ring on each nozzle (the AP kit includes the o-ring). The order of the little parts is: ball, rod, clip, so the ball is at the bottom w the weight on top of it, then the clip. I was thinking that without the clip, the weight might get pushed up too high & block the hole in the base of the nozzle???

Check the accelerator pump by supplying fuel to the carbs: prime the circuit by actuating the throttle pulley, then actuate the throttle pulley vigorously: fuel should squirt out the nozzles straight thru the carbs without hitting the carb bore walls. Each nozzle end has a hole that points towards the throttle slides.

The photo here shows the base of the pump nozzle w the o-ring.

If you don't have a manual, the following site has the 81 KZ650 pdf in the Files section.
jarlef z650

thank you so much for the pictures. after some testing i can say that the clips are certainly necessary, the carbs missing the clips are not actuating the nozzle properly. unfortunately the clips are only available in the form of a rebuild kit (roughly $30 each) x4 is pretty expensive for clips but i have a low investment in these bikes so its time to just bite the bullet and buy some overpriced parts i guess.

As for the overflow bike, i believe my problem does not lie in the petcock or float valves...but both. jeez....I spoke with a self appointed expert who told me that the condition would not exist unless both systems were at fault. I'm guessing a previous owner lost the o-rings in the float valve assembly or something along those lines, since all floats are good and points are good, I'll have to dive back into these carbs (for the 4th time) to confirm, but i suspect this is the issue. I'm just going to switch to a manual petcock when i change the o-rings, These primitive vacuum petcocks are notoriously troublesome.

while in have the post up i have another quick question. Can my factory type air filter be oiled or should i just clean it?

thanks again, you two have been a world of help.


-Calvin

Don't oil the stock air filter. It is paper and oil will ruin it You can vacuum it from the inside, but if it is dirty I recommend you just replace it. Ed

The stock air filter is paper. There is an oem KZ750 foam filter that will fit your bike --- the element fits over a holder cage, then installs the same as the paper filter. The foam element should be oiled ---I don't know if the type is superior.

Your carb guy is wrong. Even if the float needle valves & seats are good, the bike can leak fuel when parked if the petcock is bad or if it is left on PRI. I've proven it a number of times. I like the vacuum petcock, so I rebuilt mine w a K&L kit & expect to replace the diaphragm periodically as a maintenance item. But here's a topic for a manual fuel valve .

The float needle valve seats should have washers on them, but I don't know what material they should be. I don't think there are any o-rings.

I have in the past looked around for alternate clips but never found anything. Maybe you could get a junk set of carbs or bowls? ... might be cheaper.