TOPIC:

I have a theory, wondering if it makes sense. Lately the more frequent backfires when I lay off the throttle can be attributed to a clogged jet not vaporizing fuel properly, so the liquid form works its way down in the exhaust. So when I clean the carbs, the backfires will cease. Or am I just crazy?

With a perfectly clean pilot circuit, correct fuel level and correct pilot jet -- like when the bike was new -- there should be no exhaust popping when decelerating. The remedy is sometimes by slightly enriching the pilot mixture. Which can be done by turning the pilot air screws slightly clockwise to reduce the air and thereby enrich the air-fuel mixture.

Good Fortune!

Has anyone ever seen a section-drawing of the RS Flat Slide series carburetor which shows the circuits in similar detail?

Thanx!

Hey 650ed, could I twist your arm into putting up a picture of what your fuel delivery setup looks like on the bike? Knowing what the puzzle should look like will help me know what I'm doing

pa317 wrote: Hey 650ed, could I twist your arm into putting up a picture of what your fuel delivery setup looks like on the bike? Knowing what the puzzle should look like will help me know what I'm doing

The reply I gave near the beginning of this thread describes the components I use. The images below show how I have them assembled. I hope this helps. Ed

Thank you for the pictures. I did take the bike on my commute to work yesterday. Sometime after putting it in the garage, some fuel hit the garage floor. Enough that this morning, I would not have wanted to work in the garage without venting in fresh air first. It looks like it came from the overflow tubes. The choke lever was not turned all the way off. I'm guessing this is not normal and I have something else going on in addition to some clogged jets

That would affect idle.
Steve

pa317 wrote: Thank you for the pictures. I did take the bike on my commute to work yesterday. Sometime after putting it in the garage, some fuel hit the garage floor. Enough that this morning, I would not have wanted to work in the garage without venting in fresh air first. It looks like it came from the overflow tubes. The choke lever was not turned all the way off. I'm guessing this is not normal and I have something else going on in addition to some clogged jets

Fuel escaping through the carb overflow(s) is often due to imperfectly sealing float valve(s).

The overflowing may usually be avoided while parked by turning a properly functioning manual petcock to OFF or by turning a properly functioning vacuum petcock to either ON or RES.

Sometimes, running some carb cleaner in the fuel can help clean the float valves and help restore proper operation of the float valves.

An after-market in-line fuel filter is also helpful toward keeping unwanted crud and grit away from the float valve.

Good Fortune!

Regarding the carb overflow -

Fuel coming out of the overflow hose (the little hose on the bottom of the carb) is the common symptom of the 3 possible problems described below. 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

The bike is defiantly leaking fuel now. When I got home, I backed it out of the garage, to put it in the shed (so the fumes don't get into my house). In the driveway, I put it back on the center stand to double check the oil level before starting it. In that 20 seconds, a sizable spot was already created on my concrete. At least 10" in diameter. I should note this whole time the bike was vertical (stored on its center stand, backed straight out, and put back on the center stand).
On inspection, it looks like fuel is coming out of the drain screw on carb 1. I did use that screw last week to pull fuel out and see bits of rust. Should that screw have an O ring? I'm wondering if a failed O ring is the only issue. In the attached diagram, part 11 is what I removed

pa317 wrote: ... Should that screw have an O ring? ....

Yes.

The o'ring is Part No. 16038-016

Click here > www.kawasaki.com/Parts/PartsDiagram/144003/1979/KZ650-B3

Good Fortune!

Darn! Now I have to track down an O ring for that (and probably the other three drain screws)