Carburetor Grief - 1980 KZ550A

Hey everyone. New to the forum and have been reading around to get me where I'm at now. Here is my situation:

For the past week I've been working on a 1980 KZ550A. It first started with the choke on. It's idle with choke was at 4000 RPM. As soon as I opened the choke the engine would die. First thing I did was take off the carburetor and cleaned it and jets the with carb cleaner. There were not particles in the float bowls so I was optimistic. Got the carburetor back on the machine and started it back up. Same issue though. Only starts with choke, dies without. This time I checked for air leaks with the carb cleaner by spraying the boots and carburetor holders. Engine's RPM did not increase so I assume that to be a good sign.

I've now most recently replaced all the jets with those from a rebuild kit I ordered online. I also replaced the idle adjustment screws. In fiddling around with it this time I had adjusted the synchronization screws.

After replacing the carburetor I was not able to get it to start with the choke engaged. I was able to start the engine very briefly without the choke after giving it some throttle, but it quickly died out.

I'm at a loss now. I've additionally changed the oil and have fresh gas in the tank.

Where do I go from here?

Change of situation.

I let the bike rest for a while and went back and tried again. The bike would start with the choke engaged and leveled off at 1500 RPM. When I turned off the gauge it would rise to 3000, then fall and quit. I haven't come across anything quite like this in my reading. Wouldn't the low RPM with the choke engaged be an indication of an air leak? I'll have to inspect that again in the morning when I have some day light.

Any thoughts or suggestions would be greatly appreciated!

It sounds to me like a vacuum leak. Make sure when you're spraying the carb cleaner at the boots you spray towards the mating surface between the boots and the engine and not the boots and the carbs. Make sure your carbs are properly synced.

My first bike was a LTD 550, I distinctly remember that being a cold hearted monster when the engine was cold. I would adjust the idle twice daily, once when it was cold and once when it was hot. I'd double check your idle stop screw to likely back that off a it.

Have you confirmed the petcock is flowing fully?

It's a vacuum petcock, so you have to start it in the prime position, the first time, to get gas into the carbs.

Also, if you are using a paper, inline fuel filter, it can cause problems like this. You should use scintered brass/bronze, or a metal mesh/screen filter.

My signature has a bunch of manuals and carburetor info.

I'm in Chicago as well, so if all else fails, I might be able to take a quick look at it.

Hey everyone thanks for all the advice.

I didn't have any luck starting it this morning and may have flooded the engine. I'll let it sit for a few hours and try again later. I did notice a visible leak of gasoline between the carburetor holder and the engine on the outside right carburetor. Likely I'll be ordering new carburetor holders.

MTBspeedfreak, I adjusted the idle adjustment with no success this time around. I'll keep that in mind in the future.

LoudVHX, I had started the bike in prime and there is no inline fuel filter.

Should I consider giving any attention to the spark plugs? I also did not bench sync the carburetors - does anyone have any advice for doing this with the TK carbs?

Thanks again!

Bench syncing won't make much, if any, difference on starting.

If there is fuel flooding the intake so much that it is leaking out, there may be a float problem, however, it should have been pouring out of the overflows before that happened. There is a page for bench setting the floats on the TK website in my signature, under "maintenance". You can do that to get a preliminary level before doing the clear tube method (described in the manuals).

If a lot of fuel gets dumped into the engine, you may have to change the oil. To prevent this in the future, make sure the overflow drains work properly. They are also the ports you connect the clear tube to in order to set the fuel level (while the bike is on the center stand).

For the starting problem, have you inspected the choke flaps? If several are missing, those cylinders might not fire, then the one that has the flap will get too much fuel over time and flood out.

The choke flaps appear to be in good working condition. They're all certainly present.

I replaced the rebuild fuel valves/needles with the original ones to check if it would solve any overflow issue, but I had the same result as this morning. No go. The engine sounds like its just about to start, but then fizzles out. There also still seemed to be gas seeping from the engine and the carburetor holder. This doesn't seem to be an issue when the bike is just sitting though - only when I attempt to start it.

I'm at a loss.

Loudvhx, you think swapping out the oil again may prove beneficial?

Gas seeping from the engine and the carburetor holder? These things you mean?: www.z1enterprises.com/ItemDetails.aspx?i...item=IMK16065-1014X4

mtbspeedfreak wrote: Gas seeping from the engine and the carburetor holder? These things you mean?: www.z1enterprises.com/ItemDetails.aspx?i...item=IMK16065-1014X4

Correct.

Tomorrow I intend to again remove the carburetor and give it another thorough cleaning with carb cleaner. While I'm at it I'll change the oil with the assumption it has been contaminated with gas when I had the rebuild float needles in.

Will gasoline in the oil prevent the engine from starting?

I'll also start posting some videos of the experience.

Thanks everyone.

If your carbs are overflowing you may want to consider the following...

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 (some carbs don't have the overflow tubes, so fuel flows through the front and/or rear carb throat). 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 of 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