ZX6R 626 2002 idling issue and only hot on cylinder 3-4 - ZX6R Forum
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post #1 of 15 Old 03-11-2017, 05:14 AM Thread Starter
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ZX6R 626 2002 idling issue and only hot on cylinder 3-4

I have a 2002 ZX6R 636 (European model) with some issues running that Ive been trying to solve for a couple of months. The bike starts up nice and easy and idles well the first seconds, after it starts idling down so I have to give it some more idle/gas to stay alive, and after a while it starts going down again. After a while it can also suddenly idle up to about 3000rpm. The bike revs nicely but it only gets hot on cylinder 3 and 4.

Ive basically tried everything according to the Haynes workbook:
- The carbs are ultrasonically a couple of times
- Installed new spark plugs
- Installed new pilot jets (stock size)
- Ive also tried installet Dynojet Stage 1 kit
- Ive tested the coils, they are within spec. Also tried switching coils and plugs 3-4 with 1-2 without any difference.
- Pickup-coil resistance is within spec (453ohm)
- All vaccuum hoses seem to be OK.
- Compression on 1-4 is 215psi, 205psi, 200psi and 200psi.
- Fresh gasoline


Anyone had the same symptoms and maybe a cure to this issue?
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post #2 of 15 Old 03-11-2017, 07:36 AM
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I haven't experienced your symptoms, does sound like you have covered the basic's.

Once the bike warms up, have you tried confirming spark on cylinders 1 and 2.
Whats the miles on the bike, have you checked valve clearances. Did have a friend when the bike warmed up the valves where not closing completely so it no longer fired on all cylinders.
If yes, check the compression on those cylinders once warm.

Just something to think about.

My first guess is electrical, confirm spark when hot.
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post #3 of 15 Old 03-11-2017, 12:04 PM
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what have you you set mixture screws to,do you mean you start it cold then runs fine revs fine then when gets warm cuts out ant tick o/idle is very high?

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post #4 of 15 Old 03-11-2017, 12:20 PM
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Check your floats and needles and seats. Make sure they're not sticking on cylinders 1and 2.
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post #5 of 15 Old 03-11-2017, 12:23 PM Thread Starter
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The bike has 19000 kms on it (12000 miles). I checked the valves before, and I thought they seemed fine. Although i might do it again just to be sure. Will check compression and spark when its warm!

Mixture screws are set to 2 1/4 screws out (as stated in Haynes). Well, it never really gets hot (oiltemp rarely gets over 40-45 celcius), but right when i start it cold it runs fine, but just seconds after it idles down and when it gets warmer it gets more hard to start the bike.
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post #6 of 15 Old 03-11-2017, 12:45 PM
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Your coil for cylinders 1 and 2 may be bad..... switch the coils side to side, and see if the 'bad' cylinders follow the coil.... if 3&4 run good, and 1&2 then stay cold, you will have identified the issue.

"Basic stuff fellas. Use your head for something other than to break your next fall."

"There's this adage that we have 2 ears and one mouth so we should listen twice as much as we talk. Unfortunately with the Internet people have taken this old adage and turned it around. They have two eyes and 10 fingers so they think they need to post 5 times as much as they read. And since they have 10 fingers and one brain, they only have to think 10% of the time! "
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post #7 of 15 Old 03-11-2017, 12:51 PM Thread Starter
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Quote:
Originally Posted by RJ2112 View Post
Your coil for cylinders 1 and 2 may be bad..... switch the coils side to side, and see if the 'bad' cylinders follow the coil.... if 3&4 run good, and 1&2 then stay cold, you will have identified the issue.
The coils are individual and integrated in the ignitioncap. Coils are tested and switched between 1-2 and 3-4, so the coils are fine atleast!
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post #8 of 15 Old 03-11-2017, 01:03 PM
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When your bike starts, do all cylinders warm up?

"Basic stuff fellas. Use your head for something other than to break your next fall."

"There's this adage that we have 2 ears and one mouth so we should listen twice as much as we talk. Unfortunately with the Internet people have taken this old adage and turned it around. They have two eyes and 10 fingers so they think they need to post 5 times as much as they read. And since they have 10 fingers and one brain, they only have to think 10% of the time! "
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post #9 of 15 Old 03-11-2017, 01:04 PM Thread Starter
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Quote:
Originally Posted by RJ2112 View Post
When your bike starts, do all cylinders warm up?
It seems like only cylinder 3 and 4 gets hot, have tried by spraying water on the exhaust where 3 and 4 vaporizes immediately but not at all on 1 and 2.
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post #10 of 15 Old 03-11-2017, 01:12 PM
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Can you spray starter fluid into 1&2, and get them to fire?

I'm betting on a fuel problem, still. Perhaps a vacuum leak....

"Basic stuff fellas. Use your head for something other than to break your next fall."

"There's this adage that we have 2 ears and one mouth so we should listen twice as much as we talk. Unfortunately with the Internet people have taken this old adage and turned it around. They have two eyes and 10 fingers so they think they need to post 5 times as much as they read. And since they have 10 fingers and one brain, they only have to think 10% of the time! "
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post #11 of 15 Old 03-11-2017, 05:22 PM
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Since you have swapped the coils, they are OK. But are they firing once it gets warm.
Pull a coil and test it for spark once warm.

If spark then it's fuel.

If vacuum leak, small squirts of carb cleaner on sections of the carbs going to the intakes or squirts on the vacuum lines.
Normally when I ran across vacuum issues seemed to effect all cylinders. Really odd it's only two.

You have been pretty thorough, are the carbs balanced.
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post #12 of 15 Old 03-12-2017, 11:34 AM
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OP,

When you take the plugs out of the cylinders that aren't firing, are they wet with fuel, or dry?
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"Basic stuff fellas. Use your head for something other than to break your next fall."

"There's this adage that we have 2 ears and one mouth so we should listen twice as much as we talk. Unfortunately with the Internet people have taken this old adage and turned it around. They have two eyes and 10 fingers so they think they need to post 5 times as much as they read. And since they have 10 fingers and one brain, they only have to think 10% of the time! "
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post #13 of 15 Old 03-13-2017, 01:32 PM Thread Starter
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I have an extra set of carburators for a ZX6R 2000 laying around, that I though was worth to get a shot, so I cleaned them and put them on the bike. This seemed to have an effect as the bike now also gets hot on 1st, 2nd gets a little warm and it runs smoother and stays on idle, although it is a bit slow to get to idle from reving, I suspect the pilot jets are a bit clogged still, will try to install new ones and see!

But, from what i know the ZX6R -00 carbs are 36mm (and uses a bit different sizes on main jets and needles) and ZX6R 636 -02 carbs are 37mm. What difference can this make? Is it best to run with needle and jet sizes as they should be on the 2002 on the 2000 carbs, or should I install the dynojet kit I have?
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post #14 of 15 Old 03-13-2017, 02:34 PM
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Jets are one thing, needles another.

Needles can have different tapers to change how the fueling is applied. Most are not linear but will have one or more steps.

Jets will change on the mod's done. Looking at your plugs will be your main hint.
White = lean, tan is good, black is rich.
If I had to choose beside's tan it would be rich. Might get fouled plugs but your exhaust valves will thank you.

I'm a bit shocked what you have found out. Makes me think you managed to run while the carbs are cold and choked back. Once you start trying to run on main's you have issues.
Safety glasses, spraying carb cleaner with the jets removed backwards couldn't hurt.
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post #15 of 15 Old 03-13-2017, 02:40 PM
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^^OP, keep working with your first set of carbs...... you know two of them are still clogged up. The other set is completely unknown. Working on reducing a known set of variables is the surest path to success.
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"Basic stuff fellas. Use your head for something other than to break your next fall."

"There's this adage that we have 2 ears and one mouth so we should listen twice as much as we talk. Unfortunately with the Internet people have taken this old adage and turned it around. They have two eyes and 10 fingers so they think they need to post 5 times as much as they read. And since they have 10 fingers and one brain, they only have to think 10% of the time! "
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