What causes sputtering and backfire? - KawiForums - Kawasaki Motorcycle Forums
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post #1 of 9 (permalink) Old 07-24-2016, 05:40 PM Thread Starter
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What causes sputtering and backfire?

Bike: 1986 Kawasaki ninja 600r ( ZX600a or GPz600a )
Miles: 47k


I was riding the bike about a week ago with some friends. I went to pass my friend and went WOT in second gear, upon getting to about 9k RPM the bikes exhaust note completely changed. i knew something was wrong so i pulled the clutch and she barely was able to stay alive. Sounded like she was missing an entire cylinder. the second she came to a stop the bike died. I restarted and limped her home having to keep on the throttle at every light. I wasn't running a fuel filter at the time and my tank was very rusty (lesson learned)
So now once she warms up she revs and ideals fine, I can Rev her as high as i want and the throttle responds quick and fast. Once i get on the road however i have a really bad stuttering issue that begins at 4000 rpm and wont let up till about 6000 rpm. During this band the bike is backfiring and the exhaust note COMPLETELY changes tone, sounds like im hitting a wall (rev limiter). Happens in all gears at that givin RPM range. If i go WOT i can power thru it no problem all the way up to my top speed of 115 and hold that speed. Can i please just get someone to point me in the right direction?

Things tested:
Pulse Coils they were @419 and 430 ohms a piece, in spec.
Coils - Primary: 12.1v and 11.8v, 0 at key off
- Secondary: couldnt get a reading but i am getting spark on all 4
Swapped CDI with known working one, issue persisted.
Added new fuel filter and dowsed the carbs in carb cleaner with assistance from a 150 psi air machine. They very slightly dirty.
Cleaned CDI connector and Junction box connector.
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post #2 of 9 (permalink) Old 08-02-2016, 07:44 PM Thread Starter
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Bump... no one gives a damn to throw a suggestion?
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post #3 of 9 (permalink) Old 08-03-2016, 08:26 AM Thread Starter
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People over at yahoo answers suggested timimg in the ignition is off. Gonna explore that..
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post #4 of 9 (permalink) Old 08-03-2016, 09:58 AM
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Originally Posted by 86KawiBoy View Post
People over at yahoo answers suggested timimg in the ignition is off. Gonna explore that..

Is there not a forum that's dedicated to your bike? (I was on the Versys forum till the f*cking Canadians threw me out for singing to loudly at the bar!!!)
You also get a**holes like a n00b called Analog Animal who don't know sh*t about engines but because they are Liberals just want to debate politics all day........anyway, your problem:
Try, filters again, fuel & air.
Check your HT leads...the ones that come from the spark plugs
If it's a carbed model bike & you hade rust in the tank it's prolly still got some lodged in there....strip down & clean.
Take tank off, get new tank.
Get rid of all old gas/petrol.
Does it have old fashioned points?.....change then re adjust.

Don't give up or commit suicide, it's only a fkin 'bike!!!!
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post #5 of 9 (permalink) Old 08-03-2016, 05:27 PM
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I'd clean the carbs, and check for vacuum leaks to start.

Of course I'm generalizing from a single example here, but everyone does that. At least I do.

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post #6 of 9 (permalink) Old 07-31-2017, 02:18 AM
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I'm having the same problems. I've replaced the fuel pump relay, spark plugs, air cleaner, fuel filter, I've torn the carbs down and cleaned them, they were spotless to begin with. I've added a K&N air filter so I've shimmed the needles 2 shims. Each time I try something new it gets a bit better. I've got the pilot screw turned out 1.5 turns. Factory spec says 2 turns. I'm at the end of availabile fixes.
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post #7 of 9 (permalink) Old 01-12-2018, 03:24 PM
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could be the exhaust system. improper back pressure.... maybe check that for a rusted hole in the system.

Yes We Have Shoes In Kentucky... We Also Have Motorcycles.

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post #8 of 9 (permalink) Old 01-13-2018, 03:01 PM
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3 things you need for a happy running engine

1 fuel (fuel line, fuel pump, carb)
2 compression (valves, cylinder seal piston rings etc, cam clearance)
3 spark (ignition timing, spark plug, leads, coil(s))

so we can work backwards from here, side note if you don't feel like reading the recent job I did on my zzr600 which has a similar engine to yours afaik had a problem like you're describing under 5k it coughs and farts and is rough to start and then takes off above 5k it was a combination of crap spark plugs (replaced with new ones) the lead ends were dirty and the carb was full of water and other gunk.

the spark is easy just take each spark plug out one by one hold it in its lead and touch it against the top of the engine then turn her over, if you see a spark its fine spray a little wd40 in the lead end and plug her back in move on to the next one.

I doubt you have a spark timing problem because you haven't touched it (afaik)

so move on to compression again fairly easy to do a rough trouble shoot on: put the bike in neutral make sure all your plugs are in take the stator cover off and try to hand crank the engine by putting a socket on the bolt that holds the stator. ONLY TURN IT CLOCKWISE DO NOT GO COUNTER CLOCKWISE OR YOU COULD THROW THE TIMING OFF AND CAUSE ALOT OF HEADACHE...if you cant turn it your compression is good...if you have good hearing you can also just disconnect the plug leads (remembering where they should go ofc) and turn it on the starter motor, if you have a good ear you can hear the cylinders "breathing" which would mean air is passing through the cylinders right.

which leaves us with fuel: I left this last because you have 2 choices really you could run like seafoam or some other fuel additive through the engine and hope it clears (luckily for me I just ran it a mile or so and whatever it was passed through the engine burned off and was no longer a problem) OR you have to strip the carb down and give it a good clean out. you said you have a compressor so the cleaning part should be easy and carb cleaner spray can only really do so much.

My money is on water or oil getting into your cylinders (hopefully through the carb the only other place is a really bad time for you) which will throw off the fuel mixture...and if the engine is carbonized inside your pistons start to get a glowing surface which causes preignition, you CAN take the head off look at the cylinders for residue of dirt or oil but personally i wouldn't recommend it because its a pain in general cover your easiest options first but that backfire tells me the first ignition stroke didn't ignite and got pushed out into your exhaust which would also cause the second ignition stroke to have more fuel and the bike suddenly jumps forward on that stroke.

sorry its really long but I wanted to cover everything I could think of that would be causing your issues, also these are VERY rough diagnostic methods but should give you a good idea where to look good luck

Last edited by nauroticdax; 01-13-2018 at 03:06 PM.
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post #9 of 9 (permalink) Old 06-11-2019, 12:46 AM
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after market exaust?

if i die at 150 tell em i was smile n and headed for living170

life around 160
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