'99 ZX6R won't start with out petrol cap open. - ZX6R Forum
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post #1 of 29 Old 04-06-2017, 05:36 AM Thread Starter
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'99 ZX6R won't start with out petrol cap open.

Hi All,

So this issue has been around for ~2 months but has noticeably worse over the past couple of weeks. Sometimes when starting the bike it will refuse to fire unless i open and then close the petrol cap first.

It also hesitates sometimes when accelerating hard, as if it's starving of fuel. I'm guessing that this is a fueling issue of some sort but am running out of ideas.

So far the following has been completed but the issue still persists.

-New Air filter
-New Sparks
-Carbs cleaned and balanced
-Ran with a tank of sea foam

Any other ideas to try, i'm thinking the fact that i have to open the tank to start points to some kind of vacuum issue. I know the thin tube that comes out of the bottom is the vent tube but is there also something in the petrol cap that vents as well?

All advice appreciated.

Cheers

-Russ

Last edited by Rustyp81; 04-06-2017 at 06:16 AM. Reason: S&G
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post #2 of 29 Old 04-06-2017, 06:00 AM
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There should be a vent line from the inside of the tank to atmosphere to route air into the tank. That is because the fuel pump sucks out the fuel, and that causes a partial vacuum in the tank. You run out of fuel, when the pump cannot draw fuel against that vacuum.

Either that line is kinked/pinched, or the tube on the tank it mounts to is blocked. Hard to say for sure at this point which it is.... but I would expect it to be rust inside the metal tube as it's been coming on for an extended period.

"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 #3 of 29 Old 04-06-2017, 06:20 AM Thread Starter
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Quote:
Originally Posted by RJ2112 View Post
There should be a vent line from the inside of the tank to atmosphere to route air into the tank. That is because the fuel pump sucks out the fuel, and that causes a partial vacuum in the tank. You run out of fuel, when the pump cannot draw fuel against that vacuum.

Either that line is kinked/pinched, or the tube on the tank it mounts to is blocked. Hard to say for sure at this point which it is.... but I would expect it to be rust inside the metal tube as it's been coming on for an extended period.
Thanks for this!

Would there be any harm in running without the hose to eliminate any issue with it?

If its the actual spout, is it a case of draining the fuel and flushing?

Cheers

-Russ
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post #4 of 29 Old 04-06-2017, 06:53 AM
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Russ,

I would be willing to bet that there is rust/sludge clogging your fuel filter inside the tank.

I would drain the tank, remove the fuel pump and check the screen. You will need to replace the gasket when you do this.

Also, while it is off and empty, I would blow compressed air into the tank through the vent hose to clear out any potential blockage there.
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post #5 of 29 Old 04-06-2017, 07:05 AM
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If you've had the tank up at any point it's possible you simply pinched the vent line when the tank was bolted back down... Barring that, as a fix, dump the tank and follow PS's advice. Knock the easy shit off the list, and work your way down.
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post #6 of 29 Old 04-06-2017, 07:33 AM
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The '99 zx6r has an external fuel pump and filter. It could be that the petcock screen is clogged, but unlikely given the length of it.
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post #7 of 29 Old 04-06-2017, 08:28 AM
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Quote:
Originally Posted by Rustyp81 View Post
Thanks for this!

Would there be any harm in running without the hose to eliminate any issue with it?

If its the actual spout, is it a case of draining the fuel and flushing?

Cheers

-Russ
Russ,

The air vent line would be unlikely to cause you immediate mischief if it were missing..... the tortured path for fuel to get into the vent, and then dribble out enough to wet a tire or something is pretty demanding. The line is only a few mm wide.... hard to have a lot of fuel gush through that.

The metal that is formed into the nipple for the hose to mount on is unlikely to be well preserved.... because it is so small in diameter, it's difficult to coat the inner surface all the way end to end. If some condensation ever built up in there, it would be very hard to detect the rust that would form as a result.

If you can fish some small diameter solid core wire through the vent line, you should be able to figure out if it's clogged. The nipple shouldn't be more than a couple of inches long... if it has a lot of resistance (and the wire is smaller than the ID of the line) you are prodding it through some kind of gunk.

"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 #8 of 29 Old 04-07-2017, 06:15 AM Thread Starter
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Thank you all for you replies.

So, got out in the garden last night. Couldn't find anything with an id thin enough to get up the spout, but did find a can of compressed air. First few blast were met with some resistance and then something defiantly "gave" and i could hear air releasing from what sounded like the fuel cap. Confident i had just released what was blocking the breather, i moved on to stripping and and rebuilding the front Calipers.

However, once i had put everything back together, i went to start the bike.....still the same. Had to open and close the fuel cap before she would start. Went for a quick blast up an empty road to try and bed the brakes in but still the stuttering when getting heavy with the right hand.

So, am i still looking at a blocked breather or is there likely to be something else afoot here?

Cheers,

Russ
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post #9 of 29 Old 04-07-2017, 06:25 AM
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If you just blew the crud into the tank, it could have come back and blocked the line again..... shine a light inside the tank and see what sort of debris is in there.
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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 #10 of 29 Old 04-07-2017, 07:50 AM
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If the vent line stayed clear, then the issue is somewhere else.... possibly the float bowls, or the fuel filter, or a vacuum line come adrift.

"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 29 Old 04-07-2017, 09:22 AM
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Rotors could be warped, especially if they're oem with heavy use and age. That could cause the stutter

"we hold the history of the universe in our pockets..... And we use it to watch cat videos on YouTube"
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post #12 of 29 Old 04-07-2017, 11:47 AM Thread Starter
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So, this evening has been a case of six and two threes. Decided to ride home from work with the Fuel cap cracked open (Not ideal i know, but quiet roads and just over a mile), the bike started fine but again under heavy(ish) acceleration, the but really starts to splutter, it generally happens around the 8-9k mark and is quite forceful. I don think it's the brake discs as you can here the Engine noise change when it dose it, it's almost like the engine looses power for a split second.

Got home, got the tank off and had a good look in there with a torch as suggested, but it generally looked in good nick and no real crud collecting in the bottom.I Liberated some pipe cleaners from work, and gave the vent spout a good clean, there was a bit of crud in there but nothing major. Put everything back together, tired to crank it, no choke, fired first time. Happy days. Put everything back together, went out for another ride. Still the violent splutter when accelerating hard...When i got back striped the tank of again and took the petcock out to to check that the filters were not block, all looked ok.

I know this may sound daft but is there anyway to test if the fuel filter before the fuel pump is duff other than replacing it?

So it looks like the issue of not being able to start with out the fuel cap open has been fixed but the stuttering still remains.

I'm not really sure what to try next (or indeed what is going on here)...as always, all suggestions gratefully revived.

Thanks,

Russ
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post #13 of 29 Old 04-07-2017, 12:09 PM
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You don't really have any way to be sure the spark is strong and consistent.... can you tell if all of the cylinders are producing similar power? If one header pipe is cold, that would indicate a problem with that one cylinder.

What do your brand new plugs look like, now that you've run it a little bit? Clean, or fouled?
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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 #14 of 29 Old 04-07-2017, 12:21 PM Thread Starter
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Originally Posted by RJ2112 View Post
You don't really have any way to be sure the spark is strong and consistent.... can you tell if all of the cylinders are producing similar power? If one header pipe is cold, that would indicate a problem with that one cylinder.

What do your brand new plugs look like, now that you've run it a little bit? Clean, or fouled?
Once again, thanks for your advise.

It's dark now so will have to check the plugs in the morning. Last time i checked, all headers were getting hot, but will check again.

Just annoying that it's come at a time were we actually have some nice weather...

Edit: I've only just seen your second post from earlier with regards to the float bowls, will also check these tomorrow.
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post #15 of 29 Old 04-07-2017, 12:54 PM
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Quote:
Originally Posted by Rustyp81 View Post
I know this may sound daft but is there anyway to test if the fuel filter before the fuel pump is duff other than replacing it?
Bypassing the fuel filter temporarily will probably be OK, but don't run long like that. You could kill the fuel pump with trash.

To do this, you can either
  1. get a barbed hose coupler and hose clamps from the hardware store and remove the fuel filter temporarily (or)
  2. get a new piece of hose and go straight from the petcock to the fuel pump.
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