revving up to 4000 after hitting throttle.

Here we go. Got the thing and it ran all around shitty. I pulled the carbs and cleaned the jets and most the passages. The float needle was stuck in one of them, cleaned it all up, the jets, needles, and enrichments were clean. Bike idled much better, and revved up much better, but after I hit the throttle it revs and stays at about 4000, I have to play with the idle adjustment screw to get it to settle back down.

The first carb was dirtiest and had the stuck float needle. Kickstand side, it had been sitting for a year or two. I left the first spark plug unhooked (accidentally) and it idled perfect, constant even rythym. But it still revved up after a little bit of throttle. The plate isn't sticking I'm fairly sure.

So now I have pulled the carbs and am in the process of completely cleaning the entire thing. Broke the end off the top of a damn enrichment valve, but its all taken apart. The mixture screws were backed off 3 turns on the 1 and 2 carbs and about 3 1/4 on the 3 and 4 carbs. Don't know if that even matters.

So three questions. There is small pressed jet under the diaphragm, where does it go? I can't tell if its clear.

Any idea what exactly exactly would cause this revving issue? I've sprayed carb cleaner on all the boots, with no revving.

As far as the yics system goes, as far as I can tell its already been disabled. The only vacuum line there is goes to the petcock, the other 3 are plugged. So the yics is disabled right?

 

You have to be very thorough Cleaning Carbs.

Remove the Diaphragm Assembly.
Re-finish and Polish the Diaphragm Piston's Bore.

The Brass "Tube" that the Diaphragm Piston's Needle fits into does PRESS Out.
From the bottom.
Remove the Main Jet and Washer.
Push the Center "Nozzle" up and out from the Bowl side.

You may have to get a Bolt with Matching Thread and drive the Tube out.
Clean the Inside.
Outside.
Each Drilled Port around its diameter.

 

I haven't had any mikunis apart so I can't be much help there.

As far as the revving do your carbs go clunk http://xjbikes.com/Forums/viewtopic/t=1 ... clunk.html

yics passage has nothing to do with the vacuum nipples on the intake boots. Take a look at the second post on this thread to see the yics passage location http://xjbikes.com/Forums/viewtopic/p=2 ... tml#280599

 

Want your 550 to run the way it's supposed to?

Have you checked and adjusted the valve clearances yet?

I ask because you have some carb adjustment work ahead of you that will be impossible to get right if the valves aren't in spec FIRST. How many miles on the bike?

If you want it to run right, then you need to do the following, IN ORDER:

VALVE CLEARANCES in spec.

-Carbs clean; Completely gone through, religiously clean and slides pass the "clunk test."

-Float levels set and verified using fuel and clear tubing.

-Bench sync'ed.

---carbs back on bike---

-Running vacuum sync, YICS blocked.

-Mixture tuning, ColorTune, plug reads, plug chops, etc.

IN ORDER. No skipped steps, no shortcuts, no assumptions.

You need a service manual if you're not already using one. If you have one, you need to follow it step-by-step. You're going to get nowhere fast going about it the way you are.

Mikuni Exploded: http://xjbikes.com/Forums/viewtopic/t=31061.html
Valve Clearances: http://xjbikes.com/Forums/viewtopic/t=14827.html

 

Thanks fitz, the bike has 37000 miles on it.

Just to throw this out there, here's where I'm at.

Cleaned the carbs. EVERYTHING this time, diaphragms clunk, bench tuned everything,and replaced the o-rings on the float valve seats, they were done. Everything was fine as far as I could tell. Started it up and had to turn the idle screw all the way down to get it to idle about 1900. Still stayed up at 4000 after tapping the throttle.

The way of checking the float you were referring to will hopefully shed some light on this.

I'm definitely going to have to go down this list, thanks again.

 

if its hanging at 4,000 go back and clean the carbs again... it seems simple, but I had to RE DO mine 3 times till I got them perfect and to stop hanging up.

 

Honestly this is the third time ive cleaned them. When i get off work tomorrow im going to check the valve clearances because im sure theyre going to be an issue. Im going to skip the cleaning part because its been done so many times, but i might go back and replace the o-rings in the mixture screws. They seemed kind of squashed.

I'm gunna go down the list and see if i have any issues afterwards. Ill keep ya posted.

 

If the valve clearences are OK, then you might just have to clean the carbs AGAIN.
I ended up stripping my carbs three times last winter, even though I'd already done this at least three times before. Now the bike runs well.
Before this though, you might as well check the idle adjustment screw again as these are very, very sensitive to the slightest movement.

 

When I did mine I found the high rpms was the idle was set too high. I would First check your valves. Then make sure your butterfly valves are closing all the way with the idle screw not touching. You could have some misaligned. Hold them to the light and look for leaks. Your going to need to vac sync those carbs and reset the mixture. But if those valves are out of spec your going to get no where fast.

 

NOW you're getting somewhere. If the valves aren't in spec, you can't sync effectively. Period. You have to start there, because;

"Hanging idle" is generally a sync issue.

If the o-rings are little hard black flat washers then yes, they need to be replaced.

And remember you do need to block off the YICS to get a good sync as well.

It CAN be done; I've got two sweet-running 550s, and a lot of other forum members have recently succeeded as well. But you cannot skip steps or take shortcuts. It just won't work.

 

I'm one of those who succeded LOL

 

This is one of the forum members I was talking about that recently learned this all the hard way; but succeeded in the end.

Let us know what you find.

 

She runs so good LOL

 

I can't wait to have your satisfaction level, lol. I just popped the cam covers off. Getting to check the clearance s as we speak

 

Just take your time and go through all the steps carefully.

 

Double checked the clearances, I'm satisfied with my work. I'm gunna wait to pull the shims. The yamaha dealer out here doesn't open back up until next week anyway. That #2 intake was kinda borderline, not to mention it doesn't follow the trend so I'm gunna change that too. So yeah, that's where I'm at.

 

What shims are in place on #4. Some one might have the shims you need here on this site. It's about $23 a shim at the dealer.

 

20 bucks for a shim? wow.
Yeah im going to pull them here in about an hour or two when i get home.
If someone knows where i can get a hold of em cheaper that would be awesome.

 

AHEM. Reeaaalllyy?

XJ4Ever.

PM member chacal.

Click logo in site banner, upper right.

Len has aftermrket shims for less than half that; they work fine, I'm running them in both bikes.

 

Len's stuff is always great and fast. check out the pay it forward thread. Some folks have some shims to pass along too.

 

Got some shims, o rings, and a enricher plunger i broke from len. Everything was right and it got here quick. I may have just found a parts guy.

 

He's all our parts guy LOL

 

check your throttle cable adjuster too. If it's just a CH too tight it'll do that.