Carburetor Needs Choked

[SirJeremy]

So on my '89 600 motor I am having an issue that began with rough idle, not being able to take the bike off choke, or being able to even nudge the throttle without it dying. After some expirimenting and fixing a few things (like cleaning the carbs and repairing the carb boots) I've noticed that if I almost completely cover carb number 3's intake hole, I can use the throttle to rev it up. This leads me to believe I am getting WAY too much air into it. So what needs to be done to significantly reduce the amount of air being sucked in? I'm a fuel injection kinda guy, so carbs are my arch nemesis. Any help is greatly appreciated.

Oh and here's a link to a video of me testing stuff until I discover the carb revving thing:
https://www.dropbox.com/s/5t5i75qaki0do ... 9.mp4?dl=0

[reelrazor]

Clean carbs-the first go-round on that didn't work. Re-install airbox.

You don't need to restrict air-you need to de-restrict fuel.

[SirJeremy]

Well I tore all the carbs down and soaked everything in carb cleaner, checked float heights, adjusted the air fuel screws 2.5 turns out (may need to adjust them out further), made sure everything moved and flowed smoothly. With all that done it was still idling weird, and won't come off choke without dying. I synced the carbs, and tried to adjust the idle to see if that's why it won't come off choke. While trying this, I noticed even nudging the idle screw or throttle or just about anything makes the bike rev like crazy. I noticed this while trying to sync it too, but to a lesser degree. What would cause such erratic behavior?

[amplificus]

I am having this exact problem. The only way I could get it to rev is when it first starts up with choke on, the initial vroom (technical term) then I quickly twist the throttle before revs drop too low, about below 3k. If I let the revs drop below this the throttle kills it. I'll be pulling the carbs of again tonight for a more thorough clean.

Keep us updated if you find anything!

[SirJeremy]

I'm glad I'm not alone on this one. Hopefully one of us with get it figured out soon. Let me know if you get any ideas on what's going on!

[SirJeremy]

Well a quick update. I adjusted the air fuel screw out another 1/2 turn and it will start and idle with the choke off (yay!) I now have a new issue. When I rev it over 4k, it gets hung there and doesn't like to come back down. It will go as high as I like, but it takes forever for it to decide to come back down to idle. I tried moving the throttle wheel by hand, and it still hung there. What would cause something like that?

[reelrazor]

Let's start with basics:

Has it ever run correctly in your presence?

Are you letting it warm fully up before you try to throttle it?

"cleaned the carbs" comes up in almost every single carburetion related post, and is a much more meticulous process than most people think. I have seen spotless looking carbs not flow air through big passages (idle air bleeds) and without everything doing what it is supposed to, proper run condition cannot be achieved.

And, you mention "repairing the carb boots" .

All your symptoms correspond with an air leak(revs hanging high after cracking throttle) . but the fact that you say you can choke # 3 and get it rev-able tells me the carbs aint clean-at least one of them isn't.

Re-clean the carbs. Don't worry about the looks of things..just remove every jet and let them soak in the lid of a carb cleaner can while you use the rest of a can or two visually inspecting flow through EVERY passage-don't neglect the air side passages either. you need to see froth at the throttle plate idle bleed port when you blow carb cleaner through the fuel/air screw bore while plugging the upstream air bleed passage(and vice-versa)

the main jets and the starter jets will thread into each other's bores...make sure you get them right.



And, then, warm it up ..be patient, get it idling and don't touch the throttle until it is hot.

Even then, the carburetion won't be great without the airbox.

[SirJeremy]

I took the jets, needles, emulsion tubes, and air fuel screws out and let them all soak in carb cleaner for hours. I then emptied another can of carb cleaner through the carb bodies and checked each passage to ensure I could get fluid through it. I smoothed out the slides to ensure there were no rough spots and now they slide so much better. I checked the vacuum cups to make sure I had no holes or cracking. I set the float heights to as close to 22 mm as I could realistically achieve. Earlier I adjusted the air fuel screws out to 3 turns. I also made my best attempt to sync the carbs again today as well. A couple things to add to this: I discovered recently I have a stage 3 dynojet kit. I have K&N pods on the bike currently. I also have a stock exhaust with a Yoshi slip-on. The bike was running mostly correctly earlier today other than the hanging up after revving up. I had it going with no choke, and idling at just over 1k. It was still bogging a bit with throttle. It was also still idling a bit sporadically, but I hear that's an FZR trait.

[amplificus]

One thing that I learned from reading around trying to solve my issue, do you have the K&N pods straight on the carbs or are you using some type of velocity stack?

Also, I read that if your idle hangs high before settling might indicate a lean condition, and if you have high flowing filters and exhaust it might be leaning out the mixture. Did you try turning mixture screw out another 1/2 turn?

[SirJeremy]

Adjusting the idle mixture screws is how I got it start idling right. I tried adjusting it more precisely, and it ended up making it worse. I've had two people insist its the slides hanging, so I'm going to double check them. I honestly don't think it's them, though, because they are super smooth now that I went back through and thoroughly cleaned everything. I do know I need to get the "stacks" off my stock airbox for my pods, but they shouldn't be causing this much of an issue, right?

[amplificus]

Yea sorry I think not having the velocity stacks would result in poor performance in the mid-rev range due to the resonance in the intake runners, I guess it would not affect idle.

Do you have a flow gauge? I'm going to try to take the airbox off and see if the slides are all moving the same. If I can't find anything I'm going to have to really dissect the carbs and give them the full spa treatment.

[SirJeremy]

No. I don't have a flow gauge, but I'm slowly beginning to learn there are a lot of tools I need that I've never considered buying before. At the point I'm at, if there is something wrong with my carbs I am genuinely at a loss. I've taken them apart 3 times now, and each time I have pushed the cleaning and pampering even further. This most recent time I payed attention to every last detail to ensure it was beautiful. The only thing I really noticed this time around was I was missing a little o-ring like gasket in the corner of where the cups sit. Not sure what it is for, but I replaced it either way. Everything seems to be sliding or flowing as expected, so I haven't a clue what else to look at. Maybe I can get an updated video of it on my next day off so you guys can really see what's going on. On the bright side, while doing all of this I fixed some miscellaneous stuff that I hadn't taken the time to take care of yet. Located the bolt that was supposed to be holding my ignition in place, fixed my thermost, made my slip on a little more aesthetically pleasing, and found where my radiator was leaking. So at least it doesn't feel like I've made no progress this week.

[reelrazor]

One thing that I learned from reading around trying to solve my issue, do you have the K&N pods straight on the carbs or are you using some type of velocity stack?

Also, I read that if your idle hangs high before settling might indicate a lean condition, and if you have high flowing filters and exhaust it might be leaning out the mixture. Did you try turning mixture screw out another 1/2 turn?

The idle hang lean issue is almost always a problem DOWNSTREAM of the carb mouths (leaking intake boots/bad car to boot fit up), or sometimes a leak AT the butterfly shaft.

It is UNCONTROLLED AIR, not "too much air" per se.

[SirJeremy]

So I can check the boots again to make sure I don't have any cracks I didn't notice, but what exactly do you mean by "AT the butterfly shaft." Please elaborate, so I can investigate this possibility further. My other question is could this possibly be an issue further into the engine. I have heard these bikes tend to have a weak valvetrain when it comes to the intake side, but I'm not sure if any of my symptoms could be related to that. Any thoughts? Thanks for all the input so far guys. Keep it coming

[willandrip]

So I can check the boots again to make sure I don't have any cracks I didn't notice, but what exactly do you mean by "AT the butterfly shaft." Please elaborate, so I can investigate this possibility further. My other question is could this possibly be an issue further into the engine. I have heard these bikes tend to have a weak valvetrain when it comes to the intake side, but I'm not sure if any of my symptoms could be related to that. Any thoughts? Thanks for all the input so far guys. Keep it coming

It's got nothing to do with the intake valve clearances closing up in this instance.

I will leave it to reelrazor to explain what a butterfly shaft seal is, as he is the original contributor and I don't like to get him angry.........you won't like it when he gets angry.