Carb Sync YICS Tool

I found this and thought it was interesting. It is a direct cut and paste.

Comments please.



SUPPLEMENT

1984 AND LATER SERVICE INFORMATION

The following supplement provides additional information
for servicing these 1984 and later models:
a. 1984 FJ600L and LC.
b. 1985 FJ600N and NC.
c. 1984 XJ550 (U.K.).
d. 1984-1987 and 1989-1992 XJ600.
Other service procedures remain the same as described
in the basic book, Chapters One through
Eleven...........

Carburetor Synchronization

The Yamaha Induction Control System (YICS)
used on 1983 and earlier models is not used on 1984
and later models. During carburetor synchronization
procedures described in Chapter Three of the main
book, the YICS shutoff tool is not required.

 

They must of figured out it was a great big pain in the keyster!

 

Reading this forum as a resource for fixing the bike I am working on, I have seen the carb sync'n argued both ways, with and without the YICS tool.

Not knowing the answer my self I found this interesting.

I subscribe to the yes theory on the YICS tool, now I am wondering.

 

You have to block the passages somehow to do a proper carb sync. I've seen many an alternative on this site, all of which probably work just fine. Me, I prefer the actual article and have a YICS tool I purchased from chacal.

 

I read it this way - since this is a sup for 1984 and newer they are saying those bikes don't have YICS so you don't need the tool for them. It is being stated as an exception to the statement about Chapters 1 through 11 procedures being valid

 

The note implies that the YICS was no longer used? I dunno about the other models but on my 1984 XJ550, the YICS is alive and well (lettering and ports for the tool are there). I tried to synch with and without the tool and I don't get the same reading using synch sticks. Much better with the tool.

 

try it both ways, form your own opinion
only takes a few minutes once your setup, ya can't hurt anything
thats the only way to know for sure, what works best for you on your bike
the main thing is to sync them somehow, either way is better than a bench sync

 

Bill, I read it as 84 and LATER.

 

Runway, unless it an error that's what I read. I was hoping to get clarification from some of the more knowledgeable.

 

Polock, I did it with the YICS tool, after the pilot screws are set I will go back and check it both ways.

I will say this, there was a noticeable improvement after syncing a 1985 XJ550 (84 and LATER) with the YICS tool.

 

Hmm I see your point - OK I'm confused. I'm sticking to sync with the tool - I already paid the money

This will be an interesting debate.

 

Bill, I was wondering if the early carbs were not vacuume operated, perhaps the CV's don't require the YICS tool for the sync.

I stumbled across this:

Title Control of carburetor-supplied induction system

Creator/Author Matsumoto, H.

Publication Date 1984 May 01

OSTI Identifier OSTI ID: 6326979

Report Number(s) US 4445473

Resource Type Patent

Resource Relation Pat. File: Priority date 13 Nov 1979, Japan; PAT-APPL-93915

Subject 330100 -- Internal Combustion Engines; ;CARBURETORS-- CONTROL SYSTEMS;CONTROL SYSTEMS-- DESIGN; COMBUSTION CHAMBERS;CYLINDERS;FUEL-AIR RATIO;INTERNAL COMBUSTION ENGINES;TURBULENT FLOW;VALVES;VORTEX FLOW
Related Subject CONTROL EQUIPMENT;ENGINES;EQUIPMENT;FLOW REGULATORS;FLUID FLOW;FUEL SYSTEMS;HEAT ENGINES

Description/Abstract A control for carburetor-supplied induction systems for internal combustion engines.^The engine includes a carburetor and a principal induction passage leading to an intake valve and thence to a combustion chamber.^A principal throttle in the carburetor controls the supply of air/fuel mixture to the principal induction passage as a function of throttle setting and engine demand.^This invention includes an auxiliary throttle valve in the principal induction passage between the principal throttle and the intake valve, and an auxiliary induction passage extending from a point in the principal induction passage between the two throttles to a point adjacent to the intake valve where its discharge will, when the intake valve is open, enter the combustion chamber in such a way as to cause swirl and/or turbulence.^The auxiliary throttle is closed at light loads so that the bulk of the intake charge is delivered to the combustion chamber through the auxiliary induction passage.^The invention contemplates the use of one carburetor for more than one cylinder, and also a number of carburetors equal in number to the number of the cylinders.
Country of Publication United States

Language English

Format Pages: v

Rights Yamaha Hatsumoto Kabushiki Kaisha (Japan)

 

Check this out, it's not on my bike. It could be for snow mobiles for all I know.

http://www.xz550.com/YICS.html

 

Non CV carbs used a slide attached to the throttle to control the opening and thereby the fuel/air mix. Our carbs are CV (butterfly opens - causes pressure differential (vacuum) and lifts the pistons allowing more fuel). So yes earlier carbs did not employee vacuum.

But I'm not clear on your comment: perhaps the CV's don't require the YICS tool for the sync

 

1st let me state that this is my 1st experience with the XJ series bikes, so I know little about the specifics. I am still trying to learn if what I am working with are stock un-molested parts and systems.

I do not know when the CV carbs went into use on the XJ, perhaps they always did. I was just thinking out loud that perhaps because of the shared vacuum that bikes with CV's did not require the use of the YICS tool. Were the carbs non vacuum prior to 1984 on some models?

When I came across the link showing the YICS as a seperate chamber, it got me thinking. The discription makes it sound like the box is plumbed to the vacuum ports adding additional air to the intake charge down stream.

My bike draws air through the carb only, the vacuum ports on the intake manifold are sealed, I dont see how they will create aditional swirl in the intake charge.

 

All XJ's and most (if not all) XS and XV series use CV (constant velocity) carbs, either Mikuni or Hitachi brand. Some people even use newer Keihin models (with some major tweaking).

Earlier XJ's that did not have YICS, still had CV carbs. YICS was added later as a fuel saving/marketing device.

If I understand it correctly, YICS has a two-fold purpose: One is to help equalize uneven vacuum pressure in a separate chamber, another is to swirl the fuel-air mix so that a leaner mixture can be used to create the same amount of power as a non-YICS motor.

You have to use the YICS tool to "disable" the YICS chamber, to help during the sync process. Honestly, I can hardly tell the difference whether I use it or not, but then again, I don't have access to a dyno... :mrgreen:

 

We don't have an auxillary throttle, as specified in the above abstraction, which seems to be the patent for YICS. The aux. throttle would be necessary in a 1 carb or shared plenum set-up because YICS requires a pressure difference from port to port in order for air/fuel to flow thru a relatively tiny drilled passage, that induces a swirl into the combustion chamber on the intake stroke.

It seems that Yamaha included the auxillary throttle just to cover all applications of YICS.

Also, all XJ's have CV carbs, except the fuel injected models that we're so jealous of.

 

My 1981 XJ750RH SECA is a YICS bike. Syncing was a pain in the butt without the YICS tool, but I got it reasonably close. And my carbs are CV, btw. Pretty sure all of the XJ's use CV carbs.

 

Thanks everyone for the info about the CV's.

Now what about the link I posted showing the "Box" ? Is that supposed to be on this 1985 XJ550?

If so, it's not, and because it's not what's the down side if any?

My vacuum taps 1,3,&4 are capped, 2 is attached to the petcock.

How is the YICS principle working with the taps capped off. Where does/would the aditional air come from?

 

Just for trhe sake of it...
are you looking at the nipples on top of the intake boot,
or are you looking at the YICS passage under the intake books, cast into the head.

I say, If you dont like the passage SEAL IT UP....
I place a blocking tool inside and the bike runs inefficently(not performance grade)
removed- I hit the 1st gear super/duper/fired up button and the front end wheelies a bit.
I am sure you can run without the yics, but rejetting and float levels and general tuning might be required