Carb-sync problem -- carb #3 back-feeding w/ YICS tool in

The bike starts fine and breathes normally without the YICS tool in, but when I put it in, #3 carb seems to be putting out a fine fuel mist toward the air cleaner side.

Also, the Carbtune vacuum gage seems to DROP vacuum when I apply throttle with the YICS tool in. With it out, it's fine.

Any thoughts on this?

 

Have you done a compression test?

Are your valves in spec?

Sounds like maybe the intake valve isn't closing properly and the YICS is removing the blowback when not blocked off.

 

Re: Carb-sync problem -- carb #3 back-feeding w/ YICS tool i

Thanks for replying, iwingameover. I just got this bike back together from a frame-up refurb, which complicates things because everything is "new". I did a top-end rebuild which included cylinder honing, new rings, and valve lapping (with new valve springs and seals).

I also did a valve adjustment, since five of the valves were out of spec. I should be good to go in those areas. Oh, and I did a proper carb rebuild.

I've synced these successfully before without issue, but it's been four or five years, and it was in it's "old, broken-in" state. This is just another head-scratcher, and I don't like head-scratchers.

 

Clean-out the YICS Passage.

Use a Wooden Dowel and a Pair of Old Athletic Socks.
Carb Cleaner.

Open Both ends of the YICS Port.
Cut a "Patch" of Sock ... Soak it in Carb Cleaner ... and Drive it through the YICS Passage until if falls out the other side.

Keep it up: Until.
The Patch goes in Clean and Comes-Out Clean.
Now, take a Coat-Hanger.
Use it as a Tool to OPEN all the Ports.

Bend the end to a Right Angle.
Sand the end to a Point.
Put a Orientation-Bend on your end.
Probe the Port until you find the 12 O'Clock opening.
Probe clean.

Replace the Right-side Hex Plug.
Tape a Carb Cleaner Red Tube to your Thumb so it dont get sucked-in the chamber.
Run the Bike with you Thumb over the Hole and the Red Tube IN the Hole.
Have somebody hook you up to a can of Carb Cleaner.
Shoot BURSTS of Carb Cleaner in the Passage.
Quick.
Just a Burst.
Let it work.
Increase the duration.
Cleaned YICS System.

 

Re: Carb-sync problem -- carb #3 back-feeding w/ YICS tool i

Thanks for the detailed reply, Rick.
When I did the top-end rebuild and had the cylinders in my hands, I made sure to get the entire YICS network of holes spotlessly clean. I'm certain it's wide open.

 

Seca, how do you know #3 is blowing a mist out?

 

The YICS passages in the 550 are substantially larger than those on the larger displacement engines.

That ain't it.

I agree that it might be something that would be masked by a normally operating YICS.

If what's happening is what you say is happening then the only explanation is an intake valve that isn't sealing.

 

Well, when I started it after putting in the YICS tool, the carbs sounded different... more of a hiss, I'd say. So I stuck my hand behind the carbs and felt a cold, very faint "vapor" at #3. At least I considered it a "vapor" because of the cold sensation. Kind of like when you put rubbing alcohol on your skin.

I can't say there was enough "vapor" to leave my hand moist -- and I couldn't see a mist (so that was probably the wrong term to use) -- but I figured since it felt like evaporation (and not warm air) it might be fuel in a very fine, invisible mist. Then again, I'm thinking now that any air not metering correctly through the carbs would feel cold like that just by nature of how small the passages are.

And Fitz, I would think that an intake valve not closing would be feeding back warm (if not hot) air/fuel vapor. Even back-firing. Which is why I didn't keep my hand back there long when I thought it was fuel vapor! 8O

 

Regardess, if you're getting something coming back at you through the carb, it HAS to be coming backwards through the intake valve. That would mean it's not sealing right. For whatever reason. Yes, we understand you just rebuilt everything and we're not refuting that. However, you may need to check it anyway. Kind of like those of us who have rebuilt the carb rack and cleaned as if it were a surgical instrument....only to have to take it off again.....and again...... and again..........and after the *nteenth time finding a small bit they missed. NOW it finally works right.

Check the valve.....do a compression test, anyway.

You did ask what could be causing it, and we're telling you what could be causing it. Therefore, you should follow the suggestions. If you are absotively posilutely sure that that isn't the problem, then check it and give us the numbers to show us that's not it. Then, we can finally rule it out and proceed.

Let us know what you find...........

Dave Fox

 

Re: Carb-sync problem -- carb #3 back-feeding w/ YICS tool i

Thanks Dave,
I'm going to do a compression check tonight, because I do want to know what I'm dealing with. I really do appreciate all the input on this from everyone, and I'm sorry if I've come across as ungrateful or dismissive. I will be working through each of the suggestions until I've ruled them out or corrected any findings.

I'm at the end of a two-year rebuild project with this thing, it runs, it looks great, and I'm ready to ride. I've been feeling myself running out of steam with the project. I can see the light so close to the end of the tunnel that the thought of potentially needing to pull the head off again to fix a valve problem makes me feel ill. Maybe that's why it sounds like I'm in denial. I want there to be no issues, but I do know I have to rule them out.

Thanks again, everyone, for the good advice.

 

UNLESS! Damn why didn't we think of this before?

What if it's NOT coming back from the intake valve on #3?

What if it's coming from the YICS passage on #3? And not the valve itself? From BEFORE the valve?

The only way that could happen would be if THE TOOL ISN'T SEALING; so you're getting YICS "blast" back from one or more of the other cylinders.

It would also explain why it wasn't hot air, and why the bike wasn't backfiring-- it never got into the chamber, because it's coming from another cylinders' YICS passage(s.)

Is that a chacal tool or a homemade tool?

 

Re: Carb-sync problem -- carb #3 back-feeding w/ YICS tool i

bigfitz, you may be onto something! The tool is one of Chacal's tools, so it is quality, but I had torn one of the seals on it because I didn't spray it with anything before installing it (sigh). I saw that it was torn when I pulled it out, thinking that it was because it had already started melting... but I may have actually torn it on the way in without realizing it. It's possible.

And it's the seal that would have been between the #3 and #4 YICS ports.

I'm not going to use the tool again until I can get some high-temp silicone tubing. And spray it with silicone spray. Then I'll see if I still have the same issue.

Regarding the compression, I was able to warm the engine up and get some readings. Remember, these are right after cylinder honing and new rings:
#1: 92 psi
#2: 92 psi
#3: 92 psi
#4: 98 psi
Since these readings DIDN'T confirm my worst fears of valve problems, I went ahead and synchronized without the YICS tool, and did a colortune. Everything settled right in (although #4 was a little tough to get adjusted to a good blue flame without the engine hunting, so I backed it off to a tad rich).
Like I said above, I WILL re-sync when I get the new YICS tool seals, but today's success will help me sleep a little better tonight.

Thanks bigfitz -- I can tell you've spent time thinking about this. 8)

And thanks again to everyone else. I'm glad to have done the compression test, just to know where I am with it.

 

stick the tool in from the other side, see if the problem shifts.

 

It's the only explanation of your phenomenon that makes sense.

I would also do another compression test with a different gauge. Those numbers are so close to each other as to be nearly perfect. I'll bet they're really not that low.

 

You can rule-out the Tool ... by just simply "Stuffing" the YICS Passage.
Oiled T-Shirt Strip does a great job.

If you are Tuning and the Petcock is hooked-up to the No.-3 Manifold ...
Taste the Vacuum Line and see if its pulling Fuel from a leak in the Petcock Membrane.

 

Re: Carb-sync problem -- carb #3 back-feeding w/ YICS tool i

Okay, after a week of working on this issue, I think I have a likely scenario. Like Bigfitz said, I was backfeeding air through the YICS tool seal (#3-to-#4), because it had torn on the way IN the passage. I figured this out because, after I got some new high-temp tubing from McMaster-Carr to replace the seals, the same seal tore in the same place, pretty close to the same shape of missing rubber.

Turns out that the particular port where the seal seats in the YICS chamber has some extra casting material where Yamaha's machining didn't remove it. So it's not a smooth bore all the way through.

How I missed this while cleaning it I don't know. So far, I was able to get it synced pretty well, but I may have to modify the tool to move the seal inboard of the port a little more. Otherwise I have to change YICS tool seals between every use. Or like Ricko said, use the oiled T-shirt.