Carb fettling

[Jaybewan]

Now the ZX6 has cleared it's MOT it's time to focus on what is up with the fuelling.

I'll admit now that I'm completely clueless with regards to setting up and maintaining carbs so I'm a bit stumped at the moment.

Is there anyone out there who might be able to help with getting them set up or knows somewhere that may be able to work wizardry for next to sod all?

Any help would be much appreciated...

[dodgy_tom]

What's the problem?

[Jaybewan]

It's a bit complicated really. It only ever seems to pull cleanly at full throttle when cold. It seems to have a real fuzzy spot between 4.5k and 8k rpm (but only when not at full throttle) and even struggles with a blip of the throttle on a downchange. Holding a steady/neutral throttle through a corner (or in general) has it coughing, spluttering and surging.

Am I right in thinking this is the fuelling rather than anything else or am I just jumping to conclusions?

I do have a lovely new set of sparkies on the way just in case.

[alexp5]

What breed of ZX6 are we talking about? Is it standard? Race can? Dynojet? Air filter, etc?

Giz a few clues and we'll have a about it.

[Jaybewan]

It's a J2.

I'd just fitted a new standard air filter before the MOT and it hadn't run since August last year before that.

It's a standard exhaust with a bolt on scratty carbon race can. I don't think it's ever been properly set up since it was new (I know the last owner was completely clueless about bikes).

[alexp5]

I had a new J1 about 10 years ago, but we fell out with each other in a big way on a diesel-slicked roundabout... but that's another story.

I would start with draining the fuel out, including the float bowls, and start with a fresh tank of super-unleaded. IIRC there is an inline fuel/sludge filter trap doobry on the fuel hose, empty/clean this out too (I may have dreamt this... it's been a long time!)

Did you re-fit the air filter/airbox top correctly???

What's the mileage?

[Jaybewan]

I'm thinking I should've taken the carbs off when sorting the air filter out in the first place. I think it was a case of "see if it works" first.

As far as I know it's an OEM air filter element and has been put in properly (though being fitted by me usually involves some level of cack-handedness).

On it's first run out I stuck some Shell optimax in to see whether it might clean up any sludge left from a winter outside (again, wishful thinking).

Mileage is around 17k.

I've been avoiding touching the carbs as the last time I fettled anything similar was my old NC30, I still get nightmares about refitting them *shudder*.

[alexp5]

'kay.

Start with the easy stuff first and drain those float bowls. Worth checking to see if any of the rubbers are cracked and perished too, while you're down there.

edit cos I hitted the wrong button, innit: No amount of chemicals or potions will get rid of moisture in petrol once it's there. You can prevent it from forming, but draining and flushing is the only way to rid it. A little bit of water in a carb (and I'll bet it's the far left hand side one) can cause all sorts of head scratching. I would only get the carbs balanced after doing this.

[fran9r]

Sounds like it's rich in the midrange, but that could be worn needles or needle jets, and if they are like the 9 the needle jets are part of the bodies.

Or, hopefully, it could be an internal airway blocked. Definately worth a go first.

[Jaybewan]

Cheers guys.

I think I'll have to get someone with experience to look over my shoulder when I'm pulling them apart to make sure I don't miss anything/bugger them completely.

[alexp5]

This may help:

http://www.kawiforums.com/zzr600-zx-6r-old...eup-w-pics.html

[Jaybewan]

This may help:

http://www.kawiforums.com/zzr600-zx-6r-old...eup-w-pics.html

Thanks for that, it's exactly what I needed. Have some imaginary mana

[lorenzo]

You will have at lest some water in your fuel if the bike's been sat for a matter of years before you got it and it hasn't had the tank drained. Just by condensation and the change of temp from night to day will have got you a bit in there, so buy a new fuel filter (if they're the same as a zx7r of the same age, then they do some oe type fitment ones on ebay for a couple of quid that do the job nicely), drain the tank, put it in a can so you can use it for cleaning oily chains and things in future or occasional BBQ starting (useful stuff, old petrol), drain the carbs too, and while the drains are open, get a can of carb cleaner with the straw on it and squirt it in there for 20 seconds, then fill it back up with decent new fuel. The whole lot, including new fuel, will probably cost you less than £20, and will take about 2 hours to do, maximum. Once you've done that, you'll probably have a much better running bike, and if not, only then would I start looking at things like carb adjustments etc.

PS> If it has a throttle position sensor and you or a mate has a multimeter, it's well worth making sure that this is in the right place too. Again, it's quick and easy to do.

[Gregorious77]

If you take the tops off the carbs for any reason like checking the diaphragms make sure you dont loose the small o rings. they are known for falling out and getting lost.

one problem which could cause what you describe is, if a needle has come loose, this happened on my G2. the needle is held in the slide with a spring and a plastic cap with an o ring on it. if this is not fully pushed in and located the cap can pop off and the needle is free to move up and down seperate to the slide. easy to check just take the air box off pull the slide open with your finger and try to move each needle up and down, they should have only a tiny amount of movement due to being held by a spring.

micro fiche

[Jaybewan]

Right, just a quick update. I took it out for a run on Friday up the Market Harborough to Melton road to see where in particular the fuelling has issues.

After trying it out it seems to be fuelling ok at the moment, no real issues with surging or wooly fuelling in the midrange. It will more than likely need stripping down still anyway and I should hopefully get some time after Anglesey to do that.

The only thing I'm struggling with now is the idle from cold. Since I've been having battery problems (another story) and bump starting it this issue has become more problematic. It doesn't idle for more than 30secs or so on initial start up in the cold, with or without choke. I've tried adjusting the idle speed but it only really made an impact when adjusted to a rather daft amount (more on that in a sec).

The odd thing is though, once started and ridden to the junction at end of my street (no more than 100 yards or so) the problems with idling disappear completely. So with full choke on to try and keep it running I pull off down the street and as I pull up it's at a very high idle, as full choke should do. It does the same if I've adjusted the idle speed too, fails to idle outside the house then when ridden to the bottom of the street it's absolutely fine.

Would a clean out sort it? Or is it the fact that the carb fairies don't want to play outside my own house?

[fran9r]

Sounds like a choke problem...check they are all sliding freely, and if you strip them again I would use compressed air on the airways...paticularly the starter circuits.

Have you balanced the carbs? That would help the starting issues, and make for a smoother ride (mrs) too. Just did the 9 on Monday night and it transforms the bike.

[Jaybewan]

See I thought it might be the choke but it does seem to sort itself after a quick run down the road. Whether it's something not quite flowing right due to the low temp is hard to tell.

I'm hoping I'll have the time and funds to fully strip and balance them after Anglesey, just a pisser I won't get it sorted beforehand

[fran9r]

I'm thinking it's an airway for the starter blocked, or a choke not fully opening -so it would only be a problem from cold, wouldn't it?

A carb balancing tool is cheap and will quickly pay for itself.

[Jaybewan]

It could be that, hard to be sure until I get my hands dirty. Just seems odd as literally just a 10 second bimble to the end of the street sorts it...

Which carb balancer do you recommend?

[dodgy_tom]

What happens if you let it warm up and take it off choke without touching the throttle?

I'm talking about letting it run for a minute or 2 with only adjusting the choke. Will it then carburate smoothly?

[Jaybewan]

What happens if you let it warm up and take it off choke without touching the throttle?

I'm talking about letting it run for a minute or 2 with only adjusting the choke. Will it then carburate smoothly?

It'll start and tickover but won't run for long, it tends to splutter and die after about 30 seconds.

[dodgy_tom]

And does using the throttle help at all?

Another question, can you start it from cold without choke and it run?

[fran9r]

Carb tool talk: http://pbmagforum.co.uk/index.php?showtopi...=balancing+tool

[Jaybewan]

And does using the throttle help at all?

Another question, can you start it from cold without choke and it run?

Using a steady throttle keeps it ticking over, it will rev but is still rather reluctant to hold itself at idle.

I've tried starting it without the choke a couple of times and it still needs the steady hand on the throttle for it to idle or it does the same as when it's left alone with only choke. It idles for 30 secs (or less) then stutters and dies.

It pretty much feels as though the choke isn't working when it's cold (nor does the idle speed adjustment) but they both work ok after a brief run up.

Carb tool talk: http://pbmagforum.co.uk/index.php?showtopi...=balancing+tool

Thanks for that.

[dodgy_tom]

Have you adjusted the mixture screws on the bottom of the carbs?

[Jaybewan]

Nope, I haven't touched them as yet.

[dodgy_tom]

Ok, I would (in order of actions)

Remove carbs and check/set mixture screws. You can do it in situ, but you will need tiny and strangely jointed hands, or a special shaped screwdriver.

Remove and replace pilot jets with new. (won't cost you much, probably under £20)

Balance carbs.

The symptoms are pointing towards the pilot jets being blocked, and/or the mixture screws being awry.

[Jaybewan]

Ta for that Tom. I shal probably have to jump on it either monday (if I have time) or Thursday next week (again, time permitting) as those are the only day's I'll have to do it before Anglesey.

[dodgy_tom]

Good luck, the next stage is looking at blocked fuel taps, torn or slightly holed diaphragms, and loose vacuum fittings. Worth checking all of these whilst the carbs are off anyway.

[fran9r]

Always check the mixture screws when they are off, and balance them, but I doubt it's pilots. A set won't hurt, but not ticking over is more likely to be a starter circuit (I'm thinking air) that a pilot. The bike running well from slightly higher revs (not under a load, or a light load) suggests the pilots are flowing.

But for the sake of £20, it's worth a punt.