Can't restart bike...what am I missing?

Nduetime wrote: I believe I understand HOW to do the clear tube float level check but faultedgeologist has me confused. First, there's only two carbs, meaning only two drains and overflows. Second, there is only a nipple at the bowl overflow. The actual drain is a screw that feeds into the bowl. I was under the impression I need to remove screw and fill it with a tube of appropriate size, fill bowl and watch as fuel fills tube. Is this wrong?

1st) I am not the whole KZ lineup guru like some here. Make one tube per carb drain nipple and attach. That means 4 for my 4cyl, or 2 for your 2cyl.

2nd)
1-You remove the carbs from the bike, removing the gas influent line from the petcock and leaving it attached to the carbs.
2- Get a bottle of gas with a nozzle that fits in the gas tube like a catsup bottle from the housewares department. Plug it in and feed gas in through the line in to the carbs so it has to pass by the float needle. When the floats start floating, they should raise up and make the needle stop the flow of gas.
3- Raise the TWO indicator tubes attached to the nipples of float bowl above the carb assembly. They should each be about 30cm long and in a U shape coming out of nipple and going up.
4- Next, opening both drain screws a couple turns. Screws should remain in the bowls. You should see the tubes fill with gas at the bottom of the curve.
5- Slowly lower the two tubes so they fill with gas. More gas should flow from makeshift gas tank to floats, reactivating the float needle apparatus. Keep lowering after they stabilize, and compare that height to the interface of the float bowl and carb body.
6- Adjust the tang on the float that attaches to the needle. Raise the needle in relation to an installed carb if it is overfilling the bowl, or lower the needle if fuel level is too low. This means bending the tang when the carb is upside down, so think about that relationship when doing so - push down on tang if overfilling or lift up on tang if underfilling.

If one is higher than interface, gas can get in your engine and dilute oil, or airbox and waste gas, or hopefully just drain out of the sometimes functional overflow tube. If lower than spec, that cylinder will starve for gas and create a lean situation which makes hot combustion and is bad.

7- reinstall carbs and recheck float levels. Repeat as necessary.

Follow the link I provided above. This is another part of the manual, but I didn't see float spec in a glance.
www.kz400.com/Carbs/KZ400D%20Carbs.pdf

As noted by FaultedGeologist --

Some carb designs have a "drain screw" that when tight (normal) permits excess gasoline to escape through the overflow circuit out the nipple from bottom of float bowl. In other words, a normally functioning overflow circuit.

And loosening the drain screw a turn or so by-passes the overflow circuit so that all gasoline in the float bowl drains (empties out the nipple from bottom of float bowl). In other words, a normal draining function.

Am uncertain about the carbs at hand, but would experiment to see whether loosening -- not removing -- the drain screw allows the float bowl to empty by draining gasoline from the nipple.

The clear tube test will depend on gasoline flowing from the float bowl through the nipple with the drain screw loosened.

Good Fortune!

For illustration, as the carbs at hand might require level within 3± mm:



The "special tool" isn't mandatory, and may just use a length of any clear tubing that fits snugly onto the nipple.

Another illustration --




Good Fortune!

Your carbs sound like the ones on my 79 KZ750. I found a plastic fitting lying around (from a mighty vac brake bleed kit I think) that's for connecting two lengths of tubing together. It fit right inside the drain hole. I carefully screwed it in the first time letting the threads of the drain hole cut into the plastic. Attached a clear tube to the other end and I had a makeshift fuel level tool.

Like others stated, be careful about raising the tubing during testing. It'll mess up your readings. I also found it really hard to measure within a 2mm tolerance. The marks I made on the tubing tended to be wider than that. So I printed up some cards with thin mm lines. I stick the card to the carb bowl behind the tubing, hold the tube there and open the petcock. Harder to explain than it was to make.

Regarding your local shop, I got a similar response from my local shop. So you're not alone. I found it pushed me to learn more about my bike, to read my service manual and become reasonably competent at basic maintenance and trouble shooting. Oh yeah and this forum helps a lot.

If you like to tinker and solve these kinds of problems you'll have fun. If you just want to ride, you probably shouldn't own a vintage bike.

Last thought, when the bike dies and you try to restart it are you doing it with choke on or off? Since the bike's a little warm, you might not need the choke anymore. My bike is really sensitive to choke setting when kick starting. But overall I think you're on the right track by checking the float level. Would also check the screen in the petcock and replace any inline fuel filters to make sure you're getting a steady flow of fuel into the carbs.

One small thing I will interject here...Re: checking which exhaust pipe heats up first, &c.....A small "laser thermometer" would reduce the risk of permanent forearm scarring...10 bucks at any auto parts store!

Spraying water mist onto the header pipes by using a common handheld household sprayer, beginning a few seconds after starting a cold engine, will show which cylinders are combusting and which cylinders aren't combusting.

Combusting -- water mist instantly vaporizes and sizzles off the pipe.

Non-combusting -- water mist beads and rolls down the pipe.

Absent water spray, could spit on the pipes (or use your imagination), but direct contact with any part of the human anatomy is seriously ill-advised.

It only takes a couple of seconds with engine running for the exhaust pipe to instantly burn off human skin.
So DON'T TOUCH IT, unless of course you love to suffer.

Good Fortune!

have you checked the fuel filter?

Fuel filter is new.

Is your petcock vacuum or gravity feed? If vacuum to which of the 2 carbs is it connected?

On my 79/650 the #2 spark plug would foul every 100 miles, cold pipe and cause the motor to run on 3 cylinders. I did plenty of trial and error (carb clean, plugs, float bowl test, etc) and discovered the diaphragm on the petcock needed to be replaced. If you search for petcock you will find my post. It was the petcock leaking fuel to the #2 carb that caused the #2 plug to foul from running excessively rich. After the fix my MPGs went from low 30's to around 42, with more power, no backfires or sputters. I also replaced the spark plug boots, points and condensers, and adjusted the timing just to be sure. And left the old spark plug in there (cleaned up) to make sure it was fixed.

Also look at the plugs, clean them or just swap them over to find if the problem changes sides. A cold pipe is typical a fouled plug from too much or too little fuel (mostly rich). Or a dirty carb not supplying fuel, lack of compression, fuel mix issue, exhaust leak, etc.

good luck.

I might have missed something, did the OP say only one cylinder was firing? I reread the original post and you say the coils look like they came off a snow mobile. If thats not a joke you're going to need to get the proper coils. If your preliminary fuel level check was low, get a better measurement and get those properly set. And figure out if those are the right coils.

Here are some photos of my makeshift fuel level test tool. It's actually a t-fitting that I stopped up one end of. It's hard to see, but there are faint threads cut into the plastic from the first time I used it.







This works pretty well for me. My procedure is something like:
Petcock off
Remove drain screw and catch gas in a small cup
Tape card to float bowl
Screw in plastic piece
Attach tube
Hold tube against carb
Turn on petcock

A very stubby screwdriver makes float bowl removal possible without taking the carbs off the bike. You're going to have to do a lot of trial and error, as it's extremely unlikely you'll get a good result the first time you bend the tang on the carb float. So in subsequent tests, just put one of the easy to reach screws in to hold the float bowl in place. It'll be enough for this job.

I'm understanding what people are telling me in regards to being able to use the nipple to check the float height. Unfortunately, I'm not understanding the physics behind it. First the nipple extends up past the matting surface. If the float height is where it's supposed to be or basically anything under 1-2 cm above the mounting surface, the fuel won't drain out that vent nipple.
I managed to stop by Home Depot today and picked up some 1/4" barbed couplings from the drip irrigation section like this,


Slowly screwed it into the drain hole on the carb bowls. Attached some of the 1/4" tubing that came with the one-man brake bleed kit and mounted up the bowls to the carbs. Used a rubber band to hold the tubing up for a simple no-hand operation.

Right carb...


Left carb...


The left carb might be about 1cm off but I'm gonna consider my float heights to be close enough to rule out excessively low heights. One thing I did notice was there might be something up with the petcock. When I went to turn it to ON, I got no fuel response. Looked down the gas tank filler hole (gas cap was opened) and added some additional fuel since I couldn't see inside. Still nothing. Turned it to the OFF position and then up to RES. I started to get fuel registering in the tube/bowl. I'm wondering if I made a mistake when I disassembled, clean and reassembled the petcock months ago. I'll have to figure that out and address it soon. Tomorrow I'm going to hook up the timing light and see what I get. Both on the initial cold start and then after the bike dies and I try to restart. Maybe I'll shoot a video for it.