Beginner restoration of a 82 XJ550 Maxim

@Brhatweed great write up. This is roughly the process I followed to do the running carb sync with the carbtune (turn upside down if anyone with a 550 is reading this, its much more sensitive to those low vacuum pulls)

I was able to get them balanced pretty well as its warming, and then in my case once it's warm and in neutral it climbs up to like 5-6k RPM and holds. The carb sync tool still reads they are in sync, they are just running a lot higher! And its scary to have it that high for long. For the individual carbs jets if I remember it's 2.5 turns from the manual...

So my question for you @Brhatweed is that what you mean by "creeping and hanging idle"? That it runs up and holds really high? Adjusting the jets fixes that for you? I've messed with them but never gotten much of a change that I could notice.

Also P.s. tonight I took off the tank, hung the small aux tank and tried testing for a vacuum leak with propane... nothing I could notice. I started it, got it warming up with choke still on a bit, turned on the propane at that point and moved it all around the carbs and boots just to see, couldn't tell anything was off. Then as it warmed and ran itself up to 6krpm and sat there I tried the propane again, moving it around in there, stressed because the engine is going so hard, but still didn't notice any changes. Thoughts? I was really hoping to find a vacuum leak, or just diagnose this dang run away idle.

 

Creepy ot hanging idle, yes one that slowly creeps up or stays high and this would be from a lean mixture. What happens is as the engine speed increases more vacuum signal is created and this can pull more fuel up possibly from the main jet, engine speed increases more and round & round the cycle goes.
So when the carbs were cleaned (I'm assuming they were) how well was this done and any chance the passages were physically cleaned with a small twist-tie wire? One must keep in mind the overall fuel pulled during idle is but a fraction of a drop under the correct settings for each intake cycle of each jug. All it takes is something the width of a cats whisker to cause a problem here and this is why it's so important to be thorough all the way. Any chance the air bleed jets under the diaphragm cover were mixed and in the wrong places? Aftermarket books on the placement are WRONG and this is also pointed out in the tech section of this forum.
Okay so you've done the air leak checks using various combustibles around the intake boots and I'm assuming have also prayed to the YICS Gods and you still can't get the idle to settle into place then I'd recommend pulling the carbs and starting over at square-one. This means pulling everything apart methodically and making sure every passage is clear, the little sealing O-rings are on the idle needles with the little washers on the top and that the emulsion tubes for the main jets are also zestfully clean. From there verify the air bleed jets under the diaphragm are in the correct places and that the air bleed jets on the inlet horn are also clean & clear. If everything is done correctly to the factory book there is absolutely no reason for the problems you're experiencing. Hitachi carbs are not known for their ease of maintenance or simplicity however when tuned correctly they work well with little attention along the way... a something I can NOT say about the rack of Keihin carbs used on the Honda CBX and I speak from experience. That being said the effort put into the hitachi has a much higher reward factor despite only being 4-cylinders as they don't require weekly attention because they get lonely.

 

Oh the prayers that have gone up to the very stubborn YICS Gods

Maybe it's as simple as adjusting the mixture to be a little richer. I did pull the plugs and they look okay but maybe lean. Soo the only adjustments I have when it's on the bike are the 4 pilot screws on each carb, on the engine side. And underneath the carbs there is the throttle set screw. Then the balancing screw during a running vacuum sync. Manual says 2.5 turns out on the pilot screw... I'm in UT so some elevation. What would you suggest to start at for them all?

One thing that concerns me is that when it "runs up" it's not just like it's at 3k rpm, it goes up to 6k and is really humming. Would the these adjustments bring it down that much, or is that an indication of something really messed up?

If to comes to it, I'll pull the stupid things out of the pit of despair it sits in between the airbox and the engine I did a pretty full rebuild, it's possible I did something wrong, I'm generally quite organized and careful but it's possible. I think maybe one of those vaccum diaphram pistons could be acting strange... maybe a block somewhere, but it started doing this right after I reassembled and put it on the bike when it was really clean.

 

Are you not listening?
The engine speed this high needs air and fuel. So, why not adjust the idle speed screw down? For now ignore what happens when it's cold, just set the idle to 1200 or so when hot.
If you can't do this you have a build issue, remove and inspect the butterflies.
Once you have a 1200 rpm hot idle have a play with the mixture screws - even by ear you will detect a slowing idle if it's going weak, followed by a misfire if you carry on screwing it in. If this happens screw it out to regain the rpm, until it starts dropping again. Do this for all 4. Revisit the vacuum synch when finished, then redo the mixture settings.
If the above is unattainable, I repeat, strip and inspect, looking for gaps somewhere, you should be able to stop a hot engine with the idle speed screw.

 

Gentlemen, thank you all for your wisdom. The YICS gods heard my begging. I wouldn't say I wasn't listening, just trying to understand. I finally fixed the runaway idle!

Some will say, "I told you so" and you're probably right, I just didn't understand. I hope some future reader is helped by this.

The process to fix this high idle or runaway idle.
1. As everyone says, clean and set, replace rubber parts, and do all the things to make the internals of your carbs great.

*these next steps are what took me way to long to figure out

2. Under the carbs the throttle set screw, bring it all the way off so it's not lifting the throttle at all.
3. In my case the bike was running just not ideal, so I could look at the plugs and see if they are lean (white ish, dry), or rich (darkish, wet)
Because mine was running lean, this is why when it got warm it would run up in the RPMs. I was starting too high so by the time I got choke off in the warming process the lean would make it run up and stay up with the clutch in or in nuetral.
4. On each carb I turned the pilot screw or mixture screw or other things people call it. Each carb has one at the front (engine side). I turned those all the way down (clockwise) till they touch, then I backed them off 3 turns. (standard is 2.5 but because the plugs I knew I was lean and needed more)
5. I started the bike on full choke and anticipated the runup, but it never came, as I slowly brought the choke off which took longer than usual but is probably how long it should take, 5-6 min, then I reached under the carbs and adjusted the throttle set knob to get it to hold at around 1200 without me having to nurse the throttle to keep it from dying.

Boom. It worked. I went on a longer ride to get it really hot, I had to adjust that throttle set knob one more time a little lower, and then it seems to be holding. Miracles. So if you are new to this stuff, check out my 5 pages of persistent trying and keep trying till you understand what the wise sages of this forum have for you. Maybe you'll take a classic bike that didn't work and turn it into something. Like me