YICS what is it exactly? and what does it do

YICS what does it do? I dnt understand it any help?

 

Yamaha Induction Control System. It's a passage (in the head, on an XJ) that interconnects the intake passages.

Supposedly it improved something, but Yamaha phased it out. To my knowledge no one else had anything like it.

You don't really need to concern yourself with it except when synchronizing carburetors. When synchronizing it should be blocked so the bleed between the intakes doesn't affect your readings.

 

If u block it to sync carbs why wouldn't leave it blocked all the time. If unblocked u can't sync correctly then wouldn't the sync efferts change when u unblock it? Just doesn't add up to me?

 

when you block YICS to sync you are getting a "true" sync at the carbs (affected by many things inlcuding the health of the cylinders, valve train, etc.). After sync, unblocking the YICS allows a further "balancing" as hours are put on the motor. The way I look at it is its a way to maintiain a reasonable tune for longer between service calls.

 

Seems kinda weird to me.

 

YICS ...

Quoting from the FEATURES Page in the Forwards Section of the 900 Factory Manual.

"The 'Yamaha Induction Control System' (Y.I.C.S.) adds power in the low to mid-range and delivers about 10% increase in fuel efficiency. YICS is a secondary port cast into the cylinder head, linking the main induction tracts. It brings a secondary charge into the main tract at an angle so that it mixes with the main flow of fuel and the mixture is swirled completely around the combustion chamber, thus resulting in more complete cylinder filing which leads to more power and less fuel cosumption."

 

Honda. consider your knowledge broader now.

Actually Honda's system of the same vintage for autos involve a whole seperate chamber and valves to do this swirling mixing business which yammy did "without adding any moving parts"

Honda's system puts me in mind of backwards jake brakes

I wish I had gotten better pictures of my intakes viewed through the valve seats. could see the business end of the YICS fairly well. If you look at where the ports aiming at the intakes are drilled from the outside then plugged and look at their angle you can kinda tell how they swirl the toilet bowl as a fresh charge of fuel/air gets flushed.

 

Suzuki used a similar system called TSCC (twin swirl combustion chamber) IIRC. Yamaha licensed YICS to one of the European car manufacturers, too. I think it was FIAT but don't quote me.

YICS:

 

VERY nice diagram Fitz. where'd ya find that?

 

Poking about the web. It was on some German Yamaha site.

 

I knew I shoulda taken more than 1 year in highschool... oh wait, thank you google *clicks the translate button*

I've seen an awful lot for my xs400r's in german. and that repro carb site...

 

To summarize: the MPG increase is the primary benefit of YICS without sacrificing any performance. It would be interesting to see if someone experimented with blocking their YICS for a while and reported mileage before/after. (but I don't want to do it on mine, LOL)

 

Personally, I think it's why Cycle Magazine said about the 550 Seca "the Seca makes over one horsepower more than the strongest 650 we've tested on the dyno" and in the same road test, (February 1981) "to date, the Seca produced the highest gas mileage of any mid-displacement four-cylinder we've tested."

I think it's magic.

 

I'm wondering if YICS also allowed engineers to use larger valves for high-flow performance and still get baby butt smooth idle at low rpm's (low-flow) - - effectively increasing the rangeability of fuel flow control.

 

It's just a "swirler." The reason these kind of things got phased out is that manufacturers got a better handle on how to create swirl in cylinders without having things like YICS. Basically, the main way to do this is to have more valves, which most performance-oriented bikes do these days. You can also have a more complicated shape to the top of the piston, different ports, etc. They are all just ways to increase combustion efficiency and speed.

I would also agree with the comment about larger valves. The basic principle is that it's really hard to create swirl with only one intake and one exhaust valve. The pinnacle of valving is basically 5 valves per cylinder (sound familiar 700x?) but obviously that comes at a parts count and mechanical complexity penalty. And low-rpm robustness.

 

If you've ever synced the carbs WITH the YICS blocked, and heard the drop in idle speed and felt the sap in throttle response when blipping the throttle, you would understand why NOT to leave it blocked all the time. :wink:

 

To explain the "why" a little better:

When YICS is working, as you can see from the diagram, the open intake valve gets an additional "blast" of intake charge from the three cylinders whose valves aren't open.

We block off the YICS to sync, so that the "combined charge" from the other three cylinders doesn't affect the vacuum signal of the one we're attempting to adjust. With the YICS blocking tool in place, we're reading the vacuum signals from the individual cylinders alone. With YICS unblocked we'd get the vacuum signal from one cylinder PLUS whatever "combined charge" is coming through from the YICS passages.

We don't leave it blocked because that would negate the advantages of the system; IE: increased combustion effeciency, better low-mid range power, etc.

 

From what I've gathered it's kind of like Port Injection but with a Carburetor. There's a small hole directly above your Intake Valve that introduces fuel to the Combustion Chamber. It's supposed to promote Swirl and a more complete Air/Fuel mixture which results in a more efficient burn. It was designed as an emissions feature, but Yamaha says it improves Performance as well.