This Bike hates me - a tale of hateful carburetors.

My Seca is running great after synching ...NO YICS tool used

 

After rebuilding my carbs, I decided to try a synch without the YICS blocked off first. It showed that it was pretty close already and sounded fine. I then did a synch with the YICS blocked off. It required a good bit of adjustment still and sounded much smoother when I finished. The YICS system masks out of synch carbs which I guess is it's purpose. I know this thread isn't about the YICS tool but thought I'd share the test I just did.

 

That 2k rpm idle hang- just open the mixture screws another 1/4 turn or so. That'll clear it up.

 

I did mean as waldreps took it, to disable YICS while I'm tuning. My understanding is that while we know what Yamaha tried to do with YICS, jury's still out on what it actually does, for at least some people. I've got no problem with it other than the fact that it complicates tuning.
The throttle cable has been lubricated with what I understand was dry film lubricant. My throttle cable broke a month or so ago, and since I was in a bit of a rush to get the bike back in useable condition, when I chose to either order a new one and wait two weeks for delivery, or buy one from the salvage yard 15 miles away, I chose the salvaged part. I saw the owner of the yard spray something into it, though I cant recall what the can was labeled as.
I'd meant to replace the used cable with new eventually, but that thought was put to the side when the carburetor issues showed up. Thanks for reminding me, I now have a new one on the way.
For the fuel air mixture, I do think that it's likely running lean, jetted so from the factory. My understanding is that the air screws are pretty bloody sensitive, so couldn't a quarter turn be a bit much? I don't know what they are set to at the moment, what method was used to set them. I know someone pulled the security caps out of them and it wasn't me. I want to try to document where they are now as a reference, take pictures and then try to bottom them out and start tweaking, but then I hear about people breaking the tips of the needles off doing so and messing up the opening in the carb throat the needle interacts with and generally making a big costly mess I'm not aching to deal with after having been without a running bike for half a month.

 

Ok, so first, you did all that work with disassembling the carbs, but didnt pull the screws out to clean behind them? What!?

Second...count the turns as you screw them in to lightly seated if you want your reference point. No damage will be done if those directions are followed. Everyone says 2.5 is the place to start. Regarding sensitivity, some of it depends on the coarse or fine thread screws, and some of it is relative as there is no measurement for "sensitivity", just opinion. And if you open them a 1/4 turn nd its a bit too much, you just close them, back a bit, right? Its not brain surgery...just idle mixture. If it were my bike, and it was behaving as you described, that's how I would handle it. You could go "the width of a dime" at a time as some others have suggested if you felt so inclined, but to me a 1/4 turn is pretty fine adjustment. If you had the colortune, the fine adjustment might be warranted, but for a seat-of-the-pants feel, a 1/4 turn will solve the hanging idle (more than likely) and get you on your way.

 

this is a test, what is the YICS system for?

 

1. Lowered emissions.
2. Improved fuel economy.
3. A bit more power (factory claimed 15% increase over non YICS).

Trenchcoat, the jury isn't out about what the YICS system does. It "borrows" otherwise unused fuel charge from the three "resting" carburetors to induce a swirl in the combustion chamber that improves the completeness of combustion, which provides the (admittedly modest by modern standards) gains mentioned above.
http://www.xjbikes.com/forums/threads/yikes-all-about-the-yics-system.14757/

There is benefit to using the blanking tool during carb synchronization, but it's a minuscule gain (mainly to engine smoothness and emissions) and not really necessary.
Fitz would point out that using the blanking tool during a synch all-but-eliminates that annoying buzz in the huevos that most XJs have at 4k RPM.

 

1979
http://www.yamaha-motor.com/corporate/historytimeline.aspx

 

better low and mid range power, peak power is not higher, lower emissions and increases fuel economy

 

excuse me while i get the worms back in the can

 

Oh man. This is what I meant when I said "for at least some people". There is still some disagreement in whether YICS does what it was advertised to do or not.
I don't intend to disable yics, at least not permanently.

I do have that 4k vibration, and I would like to get rid of it eventually, but you are saying that a unblocked sync should in fact be good enough for now? If that's the case then I'll relegate it to "when I feel like" instead of "when I can", because I figure if it's easy I may well do it, though I'm still not sure how I'd want to do it. I've heard some good things achieved with Marvel soaked teeshirts and even bare threaded rod of a close enough diameter. What is the diameter of that passage, anyway?

Riding home from work, I was able to get more of a feel for how the bike is running. It does hang up around 2k after having been moving for a while pretty consistently, and if I let it get close enough to 1k while I'm at a stop, it does seem to hesitate a little bit off of idle. Nothing like before, but it's there. I might need to check for more air leaks, though I really don't want to use Carb clean, given how it eats rubber and I don't want it damaging old boots or new throttle seals. Would WD-40 or something else work for testing for air leaks, something that won't have the same potential to do damage?

 

Unlit propane torch.

Gary H.

 

Not any informed disagreement. Lots of uninformed disagreement.

The 4k buzz never goes away entirely, but it can be minimized. You can put off the blocked synch to a date of "someday" without any concerns whatsoever.

 

The hang at 2k man...thats not bad enough to be an air leak IMO. You have not messed with the mixture screws at all in my understanding, and that is really a pretty critical error. Its easy to do and easily reversible. Just open them a bit, the idle hang will go away. Its a very slight hang, so a 1/4 turn or less ought to take care of it just fine. A little richer at idle, thats all. And it will solve the hesitation too.

 

Nope his carbs are nor fully synched ...all opening mixture screw will do is let a little more fuel in. This is what he is fighting now if you have 4 carbs and one is admitting a little more fuel than the other 3 hence hanging idle ( and yes eventually it may idle where you want it ,but when you open throttle it won't idle back down where it should quickly). He should have made double sure in his bench synch , and then done a running synch WITH some type of synch tool ( 4 vacuum gauge/2 bottle manometer) . Just my 2 cents or nickels worth .

 

I did use a two bottle setup for my running synch. I used polocks method for the bench sync, lining up the butterfly valves in reference to the pair of ports in the top of the carburetor throats. It's possible the sync is still a bit off, but I'm trying my best to chase that zero and get all of the cylinders agreeing with one another.
I do intend to do some work with the mixture screws, probably today, once I've bottomed them and figured out what they've been set to, we'll know if I can afford to loosen them more, if they're already past three turns out my understanding is that it's better to jet up or there's something wrong, shouldn't need to richen it that much with stock jets. Once I've bottomed them and gotten my baseline info I can even unscrew them and make sure I don't have any broken needles.

 

I'm not doubting your work ,just know from experience I had a hanging idle , ended up my synch was off . I have the 4 gauge vacuum gauge set up , had trouble getting #3 to play nice . The other 3 were pulling their own weight , but where the others pulled 5 hg #3 was about 1 hg . Pulled carbs ended up butterfly was not perfectly centered, loosed screws moved plate till it centered . I then used 2 business cards cut in half( so you have 1 piece per carb) put under the butterflys adjusted synch screws until I could not pull card stock out, then backed out screw until it slid with a slight drag. Put Carbs back on . After wards only had to do a slight turn on each screw now all measure 5 hg on my gauges , it idles at 1100rpm . This was my experience and my bike would not idle right before you could back knob out and it would not drop below 1500 rpm so it would not die ( no vacuum leaks either ) .

 

A stumble just off idle can be from carbs that are set just a bit too lean. When the plates open, extra air is introduced to the cylinder before the mixture can change.
This causes a stumble until the carb can catch up with the demand.
Solution, open the mixture screws a eighth of a turn.
Thank Rick o matic for that.

 

What, no thanks to me either? 1/8 turn or a 1/4 turn, either way- its lean at idle. And the simple fix is to richen it a hair, via the pilot screws. Don't get hung up on where they are set, just open them a bit until the bike runs right.

Right right, it may be a clue that something else is off if the screws are set to more than 2.5 turns out. Mine are set to 4.5 turns out, and it runs great. Idles smooth and even wherever I want it to, no hanging idle, no hesitation, no missing or popping, just smooth acceleration that makes my eyes water. Plugs look real nice. What more does one need?

 

Gentlemen. There are a lot of things that can cause a hanging idle. Let the man work through the suggestions offered instead of arguing over what the cause is.