These Carbs are Kicking My Butt. Won't hold Idle

[MagicNinja]

So I've got a REAL finicky 1992 600r. It has a yoshi pipe and has be rejetted. Main jet size is 112.

Let me start by saying it has a dismantled airbox from Mr. Previous Owner. The box and boots are fine, but there is no top or air filter. WIth out the box on, it runs like crap. It is a little better with the box on, but it runs the best when I shoved a filter in it.

I have cleaned and completely rebuilt the carbs. I am running it on a test tank. There are no unplugged hoses, the throttle and choke cables both have slack. When I rev it up it its ok but when I let go of the throttle it hangs at 3000 rpm and won't drop. Sometimes, when it does drop it still hangs for a bit at 3000 and then drops to idle. Idle is extremely rough and fluctuates wildly before just dying.

I've been messing with the pilot screws, but no matter where I put them, it still hangs before dropping to a bad idle. I'm pretty sure its not leaking air around the carbs.

I'm stumped. This is a tricky little bike.

[StarGate]

Hanging idle can be caused by running too lean. It's also been reported on here by many ninja owners that they run like crap at idle and low end without an intact air box. Since you are missing a lid and it's been rejetted I think you are going to have your hands full trying to get it to run right.

[MagicNinja]

Well the only jets that were changed was the main jet. its a 112 stock is 105. The pilot is a number 35, its stock. I've been playing with it and there no leaks around the boots. I've put in a temporary air filter and I'm thinking maybe its too much filtering. I can get the idle to drop down without the filter thought it is really rough. Without the filter it runs terrible at any RPM. WIth the filter installed it runs awesome but won't come down to idle. If I turn the pilot screws out more, it hangs for less time than with them screwed in but I have them turned out 3 turns. Is it acceptable to turn them out more? 3 turns seems too much and its still not where it should be.

I'm convinced it has something to do with the backpressure from the airbox but I'm having a hell of a time even getting it in the ballpark. I need your guy's help.

[Bob Myers1]

if 3 is better than 2 turns then 3 is not too much, try 4 or 5. You may end up changing the pilot jet to ever get any closer

[joshp1840]

try synking the carbs also

[MagicNinja]

I can't keep the bike running long enough to sync, though they have been visually synced. Thanks for the reply. Keep the ideas coming guys.

[StarGate]

Originally Posted by MagicNinja

I'm pretty sure its not leaking air around the carbs.

What you you think if you had a mechanic rebuild your engine and after doing so it didn't run right. Then he told you he was pretty sure he installed the rings on the #3 piston? There are some things you need to be positive of and for a hanging idle this is one of them. If you haven't used some starting fluid, WD40, or other means to test and ensure there are no air leaks (this includes vacuum lines also) you will end up like a bulldog chasing his nub tail. If the manifolds and boots are not new then there are very good chances you have an air leak. I'd also say you should put the stock jets back in and find a lid for that airbox.

[MagicNinja]

I have used starting fluid. No leaks. Do not have stock jets Mr. Previous Owner rejetted, the problem has nothing to do with the main jet, which was the only one changed. I'm thinking I'm going to have to get all the other parts of the airbox back but they are ridiculously priced. What can cause this problem if there are no air leaks. Valves, spark, and compression are good as well.

[StarGate]

The only other things that come to mind atm are throttle cables being too tight or a sticking butterfly in the carb.

[zoro]

Originally Posted by MagicNinja

I have used starting fluid. No leaks. Do not have stock jets Mr. Previous Owner rejetted, the problem has nothing to do with the main jet, which was the only one changed. I'm thinking I'm going to have to get all the other parts of the airbox back but they are ridiculously priced. What can cause this problem if there are no air leaks. Valves, spark, and compression are good as well.

It dont take much of a leak to cause a lingering idle. Sometimes the rubber grommets and seals around the throttle and enrichener linkages can leak. One issue I had was my carb holders were not staying tight at the head. I applied a thin coat of high temp silicon to each carb holder face and a drop of blue thread locker on each screw and that cured the problem.

[joshp1840]

105 is the stock main jet and 35 is the stock polit jet according to our parts look up at the shop. not sure about clip setting on the needle. i would also soak each carb and reclean u need to be 100% sure everything is clear but thats just what i would do

[MagicNinja]

Yep. joshp1840 you're correct. It seems the only thing changed was the main jet. Stock needles are also there, so no clips. If I ever get it to idle I'm gonna shim it out with washers for mid range.

Atm I'm still stuck as to what would be causing the idle problem. If I didn't know CV carbs don't work well with pods, I'd just drop some on. Im 95% sure the problem has to do with incorrect backpressure from the airbox. I've been fiddling with various mediums to use as filter material to try and reconstruct the airbox. The replacement parts for it are ridiculously priced. I was using egg crate padding that is used for bedding lol. But it has solved a lean running problem with my 250 that had a dismantled air box.

I am thinking it's too thick and that may be why I can't get it to drop down to idle. like its choking too much. As soon as I remove the filter it drops down, but idles real rough and dies. Also withouth the filter, the power all the way across the band is terrible. After looking at picutres of the stock filters, they seem to be about 1/4 inch thick material, the filter I'm using is about 1 inch thick. So I'm thinking its restricting too much air. If anyone runs across any used airbox pieces let me know, I don't have much of a budget to work with.

I am positive there are no leaks, I have sprayed starting fluid all around the airbox, no RPM change. The carbs are shiny clean and no jets ever get clogged.

If I can get in the ballpark, they will be synced to even everything out. I've never had this problem before, and I'm really good with carbs. Since I've had the 250, I am extremely familiar with Keihin CV carbs. Its just that now there's four and its real finicky.

I guess its just continuous trial and error. I will keep you guys updated, but keep the input coming, its' greatly appreciated.

[A-J]

Your problem is apparently a lean condition. This is typically caused in one of 2 ways - wrong size jets, or air leak somewhere. If you follow what others have said about spraying wd40 or other similar fluid around all joints and don't hear a change in the idle then it's the jetting. More specifically, it's the pilot jets, or rather the holes in the carb where the pilots sit. Your 92 should be pretty simialr to the old school 250 carbs, and I would bet you that the pilots are at least partially clogged. You need to pull the carbs and clean them again. Remove the pilot jets and idle screws and drip some hard core cleaner into the holes where you pulled them from. I say drip, because then you can actually watch the fluid level. If it disappears immediately, then that particular hole is good. If it does not, fill the hole and wait for it to drain, then do it again. Once it drains the second time (which should be faster) blow compressed air through it. Repeat as needed until the fluid does not collect. And unl;ess you're going to remove the airbox completely, you're going to have to knuckle down and buy the missing parts. Or at least fab up a close match.

[MagicNinja]

I have cleaned, dipped, and blown compressed air through these things several times. I'm running on a test tank as well, so there is no contamination from the tank. The carbs are clean clean clean. No clogged jets or passages. I think you're right though. If I got the airbox assembled completely I'd at least have a starting point for tuning.

[knucklebuster01]

I'm gonna go ahead and say that my 95 zx6r does not function properly without the air cleaner box properly installed as well as the vacuum lines that go to it. Specifically the one that goes to the air switch, which in turn connects to the intake of at least one cylinder and elsewhere.