XJ550 Carb Q's

I feel bad making a carb thread when I see a ton already posted, but I have some specific questions I couldn't find any concise answer. Carbs in question are mikunis.

I've got my carbs mostly disassembled... they're still together on the rack, but everything sans the pilot jet is removed. Waiting for sears to open tomorrow so I can buy a screwdriver that'll get in that tiny opening. Anyways.

I'm fiddling with bench syncing them, and I cannot for the life of me get them to all open at exactly the same time. I've messed with paper clips, strips of cardstock, and trying to eyeball the passages on the tops of the bodies. But no matter what I do, when I slowly crack the throttle, one always lights up a little bit later than the rest.

So far my best results have been using four paper clips, and trying to get them to all drop at the same time...

How important is it that I get them all within micrometers of each other for a baseline? That is, I can just toss them on, and get a bike that'll idle well enough for a proper sync and that will respond to pilot screw adjustments..

Lastly, what's a good starting point for setting the initial idle? I believe you want to leave one and a half of the three grouped passages on the top of the throat visible?


Crossing into the pilot screw realm, I've learned that turning in makes things leaner, and turning out makes things richer, and a starting point is 2.5 turns. Good to know.

I've read Rick's guide on tuning by hearing, and it seems to make sense. Turn things out until it gets enough fuel to match the amount of air incoming, reducing gross throttle to keep things steady at 1k rpm. This seems like an awful lot of work, with lots of trial and error.
So, taking the lazy way out, how much faster and easier is a colortune plug?

 

Sounds like you have them close enough to put them on and get it running so you can do the final sync', they just need to be close for a bench sync. I have hitachis, 2.5 turns was baseline for me and the colortune worked well, will try Ricks by ear method one day. Make sure you have got them CLEAN with a capital C, all the nooks 'n crannies.

 

Obviously, the closer you get with your initial bench sync the easier the running vac sync will be.

I didn't think much one way or the other in regard to the ColorTune until I got one; they make the job much easier (at least in my experience.)

 

yeah, I'm trying to make things as painless for myself as can be. Kinda dumb considering I'm not gonna be riding much longer - but knowledge that things are squeeky clean and working right before storage is some comfort.

My biggest question is setting the initial idle point, I have no idea how much the plates should be open for your basic, smooth idle. I guess I could experiment after I've put the carbs on the bike? I'd like to keep all the possible 'no-starts' to a minimum, though!

 

About 1.5 turns most, would be my estimate, based on once its running well it doesnt take much turn on the knob to change the revs a coupla 100.

 

If you still have one butterfly that appears to be "sticking" or opening later than the rest, than your adjustments are still off.

Adjust your idle screw all the way off, then slowly tighten it down until three of the four butterflies just barely break the seal and let some light through. At this point, the fourth one will take longer because it is set back further than the others. As soon as the light breaks through on that last one, the others should have a larger amount of light shining through, and you need to adjust those back to the "latest" one to have light break through. The reason is, that the latest one is your base of movement.

Here is the caveat with that procedure. If your adjustment is way off, the last one to break open may be the wrong one to use as the base of movement. Since the #3 carb has no adjustment, it is the one that is controlled by the idle screw, and the rest should just follow it due to the linkage and adjustment screws.

I have also found that I don't need strips or paperclips, or anything else to help me measure for a bench synch. You can use a light from behind and compare the light dispersion below the butterfly gaps, at least to get it close enough. To be honest with you, I have always had to make more than minor adjustments even after bench syncing because each cylinder has its own operating characteristics while the bike is running.

When you are synchronizing your carburetors, you aren't really synchronizing each carburetor to the others, you are making up for slight differences in each of the individual cylinders needs, so you are actually syncing the individual carb to that cylinder so that it behaves like the others when you twist the throttle, which obviously controls all the carbs together equally.

I guess my main point is that each of the butterflies can open to the exact same spot to the thousandth of an inch, and they may still not be what the engine needs, and doesn't mean your carbs are synched. Just get them close enough by eye, or something else if you want to measure more closely, then use vacuum gages or sticks get it spot on.

 

Since you're having a bit of difficulty, the one other thing I'd suggest you check for is any play or slop in the butterflies relative to each other or the carb bodies. If they're not tightly coupled you'll have no luck getting them consistently vacuum synched later.

 

Checked for slop, and things are pretty tight. I think my problem is that I'm thinking in quarter turns and such on the adjusters, rather than tiny little tweaks. I'll get the hang of this eventually - perhaps I'm just trying to be 'too perfect,' and human error is getting in the way of things?

 

Alright - I'm very happy with myself; I managed to get everything apart, clean it, and back together and have it start with ease! It also finally idles with the choke off.
Carbs passed the 'clunk test' as well.

However, now I have a nasty hesitation off idle that will sometimes kill the engine. I twist the throttle then sometime after it'll try to catch up, then sputter and finally rise, or just dies out. I wasn't able to do much diagnosis as its 1:30am, and I don't think my neighbors would like me tinkering with that at this hour.

So my engine is running really lean or rich? I'm not sure which. I'm assuming I need to idle it for a bit then check the plugs to see which direction I need to go?
Also, before I cleaned out the carbs, the bike would not idle without at least half choke, but even with the choke all the way off, if you snapped the throttle right before it died it'd fire up without any bogging or hesitation.

 

Well guys I made a dumb mistake, I forgot to check the float levels. One and four were fine, three was a bit low... but two... two was a big surprise. When I got to number 2, and opened the drain screw... I noticed the fuel level shot up to the top of the intake throat.

At about that same time, I smelled gas rather strongly, looked down, and saw a nice puddle forming. It was dripping like mad out of the intake box. I quickly turned the petcock off and pulled the rack.

Pulled that float bowl, didn't notice anything out of the ordinary.. fiddled with the needle a bit. Tried it again with a test rig on my bench, and fuel was pouring out of the idle passages. Holy smokes.

Took out the new needle and socket I installed, and replaced it with the one I pulled out. Retested. No leaks, hurray. Once the leak was taken care of, the number 2 float was spot on. Adjusted 3 and put the carbs back on the bike, and am calling it a night.

Amazing how forgetting something so simple can bite you in the ass so hard.

 

Got a bit more done tonight. When I adjusted the number 3 float I guess I messed something up and it started flooding out, too.
After rectifying that, I buttoned everything up, started, and prayed. Fired right up with the choke on, then the RPMs flew up almost immediately, and stayed up until the choke was almost completely off, then started dipping. Completely removing the choke/enrichment would kill the engine pretty quick. Fiddled with the idle speed screw, that didn't help much.
Opening the throttle slowly would cause it to hesitate a bit, then catch up. Snapping the throttle would kill it fast.

I pulled the plugs and they were lookin kinda white, so I figured things were a bit lean. Turned out the pilot screws to 3 turns, and while it would still die without choke, it wasn't quite as quick, and the hesitation was reduced a bit, but would still kill with a sharp snap.

I spritzed a bit of starting fluid into the intake while I stopped it from dying with a bit of throttle, and the RPMs soared to 7k, and stayed up even after I let go of the throttle. I killed it, then restarted the bike. I checked for vacuum leaks all around, and couldn't get the rpm to change at all no matter where I sprayed, so I think I might just have the idle speed screw set too high. I looked for a way to tell when the screw touches the throttle assembly after I killed it for the night, but no view that I can find allows me to see that... so I'm trying to base things on watching the intermediate throttle cable slacken/tighten, which is who knows how precise...

Back to the pilot screws, is it unusual for the XJ550 to have to turn out the screws 4 or 5 turns? And what is the 'range' on the screw, before turning it out has no effect?

I can't do any more 'live testing' tonight since I think the neighbors have had enough of loud motorcycle at midnight for now.

 

Your bike is doing exactly what mine was doing when I got the carbs put back together except for one thing. It sounds like your needles are taking turns sticking in the brass seats. You need to polish the seats. I use some metal polish on a q-tip cut in half and chucked into a dremel tool.

Now to tackle the revving problem. First you need to properly sync the carbs with a set of gages. Vaccum gages, mercury sticks, other sticks, whatever. Once that is done properly, the rpm's should drop back down to a reasonable level provided you don't have the idle screw cranked way up. Once you have a good sync verified by the gages, you need to take the bike for a good spin. Maybe ten or fifteen miles or so, and then, and only then, can you adjust the idle down (or up) to where it needs to be.

If you try to adjust the idle by simply letting the bike warm up in the garage, you will forever be chasing your idle. Ride the bike, then adjust the idle, and don't mess with it anymore. If the bike seems to want to die before you have fully warmed it by riding, you simply need to leave the choke on a little longer, at least partially, until you have put a few miles on it.

 

You're talking about the float needles, correct? Not the main jet needle and its seat? As much as I'd hate to take the carbs off yet again, I guess its something that I should do to rule out the possibility that things are sticking?

For the time being, I don't have a tool to sync the carbs up. Don't you need the bike to achieve a steady idle before you sync it? I was under the impression it was a 'finisher' of sorts, and it was possible to get a decent idle without its use.

More than that, if I can't get the thing to idle at all without the enrichment circuit, does that mean I should go back in and perform another round of cleaning? I do remember when the #2 carb was flooding bad, the thing idled rather well at 1200rpm, and now I can't get it to idle at all.

I'm really quite the novice when it comes to this, so I'm not sure what to do, honestly. It's frustrating having to take shots in the dark, trying to correct a problem. Tomorrow I think will be a long day of trial and error for me. No work means I get to play with the engine and carbs all day long.

 

Yes, the float needles are what stick and allow fuel to drip or pour from the intake side of the carbs and drip out of your airbox.

The synch/idle thing is kind of like a catch 22. But if your synch is off at idle, it is going to be even more off at higher rpm's. So you can synch with the engine running high, then back the idle off, then check/adjust the sync again, back it off some more, check/adjust the sync again. You get the picture. Then when you are close to a normal idle and all the gages are reading the same, you can take the bike for a good warming up spin and adjust the idle for the last time. All this back and forth is actually what you are trying to avoid by bench syncing but it doesn't always work.

If you aren't sure your carbs are completely clean, and you think that might be why it won't idle with the choke off, then yes, you need to go back through and make sure the entire carb assembly is super clean.

Also, looking at your original post. I would recommend getting a set of vacuum gages before I got a colortune plug. The gages are going to help you much further along than the colortune will. You might even be able to rent a sync tool from your local mom and pop motorcycle shop if you don't want to spend the coin and get a set to keep. The colortune can be difficult to read, it has a bit of a learning curve to it, and you can accomplish the same thing by using standard turns out on the mixture screws and adjusting by reading the plugs.

Personally, I think the colortune is somewhat of a gimmick, because it is only showing you what the flame looks like with the colortune installed. That doesn't necessarily mean that is how the cylinder is burning with the actual spark plug installed. There is no way you can get that colortune to match every kind of plug characteristic that it is marketed as being compatible for, simply because the threads match and it will screw into a engine. That is just my opinion though.

 

I have a single automotive style vacuum gauge, I suppose I could do a simple check with golf tees for quick line swaps or something. Not sure what to use to quiet down the pulses, though. Maybe figure out how to put a restriction in a bit of vacuum line. I wonder how accurate that will be without a YICS tool, though... I plan on getting a gauge set and that from Chacal later this week, actually.

What I can't figure out is how the bike developed hesitation in throttle after my cleaning.. one thing I am kicking myself for now is not writing down how many turns out the pilot screws out were before I removed them.

Thanks for the advice BDM. This is all such new territory to me. Growing up on fuel injection spoiled me something fierce.

 

Thinking about how folks like BDM told me to ride it before tinkering with the idle, I decided to go out for a ride. Neighbors be damned! I did my best to guesstimate when the idle speed knob was off the plate, then carefully turned it in about one and a half turns. Maybe two - I couldn't tell honestly.

A cool 43 degrees out and windy as heck, but at least she still starts quick. RPM didn't rocket up to 7k, so hey, I fixed something at least.

I'm cruising around with the choke set to around half for a few miles. This is the point that I typically had to run before I attempted my cleaning. I noticed it was a bit... down after a little while though. Didn't have the same pep it had before. Thinking I buggered things more with my clumsy carb work, I decided, on a whim, to completely turn the choke off. Suddenly, the old engine under me came alive with renewed vigor. Above 4k the throttle response was more or less instant. The RPM would snap down without any sluggishness. Cool. My thoughts now turned to the dreaded and terrible 'curse of the idle.' I found myself a parking lot, eased in... and completely pulled in the clutch and kicked it in neutral. I was expecting the usual chugga-chugga-gasp-die like it always had before, but to my surprise, it stayed alive. I sat and just listened to it for a good minute. It was a labored idle... a bit high, a touch over 1500 - at least, according to my noisy, sticky, and shaky tach. Still, it was running without throttle, and without choke. It wasn't a very pretty sound, it was galloping, but steady, and I could kill it by revving it quickly, then snapping the throttle closed. The RPM would drop and dive under that idle point. The engine would struggle, surge, sputter, and come back up. Sometimes.
If it died under these conditions, it required about 3/4 to full choke to bring it back to life. Once it came back up and stabilized, if I removed the choke all the way again, it'd conk out. It needed a bit of time before I could completely remove the choke.
I thought about tinkering with it, but it was cold and windy, so I decided to bring it home.

I let the engine idle for a bit before killing it when I put it away. I'm waiting for the engine to cool, as I've always been extremely cautious when it comes to removing or installing spark plugs in freshly-baked aluminum cylinder heads, and I'll post some pictures of the plugs for you guys, so you can guide me towards success.

It's better than it was, and I'd like to thank all you guys at this website for that.

 

Pictures are about 1.5mb each. 2272x1704!
http://img11.imageshack.us/img11/8162/img0163cx.jpg
http://img202.imageshack.us/img202/5972/img0165hk.jpg


This plug read was done at something like a 1500-2k rough idle. I suspect things are very lean, but I'm not sure. As you can see, they're almost pure white on one side, and colored on the other.
I've already got the pilot screws three turns out, is it unusual to get them out much more?