Kz440 no start puffing out of carbs

Hey new here

Bike: 1981 kz 440 A2

Ok so i tried to start it. this was my first attempt. it continually poffed out of the carbs and then it eventually back fired.

What is the deal?

I have the carbs out again and i am cleaning them again.

Could my firing order be out of wack?
If so which plug wire should be on top and which on bottom?
Does it matter what order the wires going to the coil are?


What would cause the puffing(little puffs of smoke are emitted) out of the carbs?

I did the coil mod and i am getting 12volts at the coil. the sparks seem a little orange could the wires being old do that?

new gas, new inline filter, new plugs

toates89 wrote:

... 1981 kz 440 A2... back fired.

Could my firing order be out of wack?
If so which plug wire should be on top and which on bottom?
Does it matter what order the wires going to the coil are?

What would cause the puffing(little puffs of smoke are emitted) out of the carbs?....

Hello toates and WELCOME to KZr!
We're glad you're here!


Dual wire coil fires both sparkplugs simultaneously, so it doesn't really matter which plug wire goes to which plug.

Also doesn't matter which of the small wires to primary coil terminals are connected, so long as one goes to one terminal and the other goes to the other terminal.

If not already done, would measure the valve clearances, especially the intake valves, and adjust them as needed.
An intake valve with insufficient gap may be failing to fully close and thereby allow combustion within the cylinder to backfire out the carb.

Old hard leaking sparkplug wires are of course not good, but I don't suspect either the condition of the sparkplug wires or quality of spark at plugs is causing backfire through the carbs.

Good Luck!

well i already did adjust the valves all are in spec cept the left exhaust which is only minimally to loose(will readjust after i get it running)

i just had the carbs apart and i noticed that the diaphram was ripped in one of them and i also forgot to attach the vacuum line from the carb to the petcock.

could the vacuum leak cause it to do what it did?

Ok so i just called kawasaki and they want $200 for each vacuum slider.


thats outrageous

so if i went to a one carb setup what would my options be?

If this bike has a mechanical timing advancer that could possibly stick or hang in the advanced position whereby the timing is not retarding as it should at idle rpm, then under circumstances of being in the advanced position when attempting to crank might possibly cause popping back through the carbs.

Am just guessing that this might be something to consider.

Perhaps dead wrong, but I don't suspect either the carbs or an air leak associated with the carbs. Regardless of carb condition or fitment. And a single carb to replace the dual carbs won't resolve the backfiring issue.

Air/fuel mixture from the carb is of course sucked from the carb through the intake port into the combustion chamber. As I understand it, backfiring through the carb originates in the combustion chamber. The combustion "explosion" inside the cylinder is not supposed to go back out through the intake port into the carb. If it does, its only route is by first getting past a supposedly closed intake valve. This may occur regardless of correct ignition timing at idle rpm, because even with proper valve clearance, a damaged valve or damaged valve seat (failure to completely close) may allow the backfire.

Improper cam timing could cause the problem, but doubtful here where there's been no reported problem with the cam chain or mechanical work done in the cam area.

Let's say the cam timing, valve clearances, valves and seats are all okay. Now, if the combustion inside the cylinder happens at the wrong time (i.e., before the intake valve finishes closing against its seat), part of the explosion may go back out through the intake port and carb. Am thinking this bike has its timing already permanently set, which left me with nothing but a guess as to possible incorrect timing at idle rpm due to some fault in the advancer system.

If there's a way to check the ignition timing with a strobe type timing light, would do so, and also verify that the timing is advancing and retarding with changes in the rpm.

Nothing else has yet come to mind.

Good Luck!

Has a compression test been done? Or better yet, a leakdown test?

Is it backfiring through only one of the carbs or both carbs? If only one or the other carb, could help isolate the problem to one particular cylinder.

Patton wrote:

... If there's a way to check the ignition timing with a strobe type timing light, would do so, and also verify that the timing is advancing and retarding with changes in the rpm....

Well Duh :S Just remembered that the bike won't crank. Perhaps there's a way to do a static timing check to assure correct ignition timing.

the story of the bike is it sat for 15yrs i rescued it replaced tires battery, i did replace the Automatic timing unit and lubed it well so i know its not sticking. i am getting 12 volts at the coil.

spark is mildly blue more orangey

what position is the petcock supposed to be in when attempting to run?

the bowls do have gas in them and carbs arent leaking any gas



no leakdown test or compression test has been done, i dont have the tools

since the valve clearance has been set, is it possible to examine valve seats?

toates89 wrote:

since the valve clearance has been set, is it possible to examine valve seats?

On some models it's possible to reinstall the advancer 180 degrees out which causes backfiring through the carbs. Perhaps that happened in this case.

Some local auto parts stores loan out test equipment. Could call around and inquire.

A compression test or leakdown test will indicate whether or not a valve is leaking. To visually inspect the valve seats would require removal of the cylinder head.

Petcock handle pointing down = ON, up = RES, to rear = PRI

Good Luck!

If the slide diaphragm is torn, the bike will still start but won't accelerate as it should. The main issue would be the missing vacuum line. The one carb will be extremely lean and you may not be getting any gas if the petcock is in the ON position. Put the petcock in prime PRI to start the bike so that the bowls fill. When you get it running, switch to ON.

ok so now it doesnt puff out the carb unless the choke is on all the way. then it pops them open.

i did repair the rubber part of the slider with duct tape for a temp fix just a small 1mm x 1mm piece on the hole.

i took off the valve covers and turned it over and the valves seems to be moving freely but i guess ill do a compression test.

i have a feeling its lean because its not getting gas. the carb bowls are full but does that mean it should be getting gas?