YICS System

[Venturous Randy]

As part of trying to get rid of the off idle skip on my 83, I removed the hoses and plugged the ports on the YICS system. The bike runs so much smoother and I can not tell any significant difference in power, so what did the YICS system actually do? I noticed on the 86 engine that the ports are not even machined for a tube for the hose.

RandyA

[Denden]

The YICS system shoots a small jet of air/fuel mixture into the combustion chamber at an angle. it is supposed to induce swirl in the combustion chamber.

When the intake valve closes, it creates a small positive pressure, which goes up the tube into the plastic YICS chamber for that cylinder. On the next cylce, when the intake valve opens, that positive pressure shoots into the combustion chamber...swirling the mixture for more complete combustion.

I've tried blocking it off...the motor seems to run just fine and smooth. But as I recall, I got very slightly less mpg's, and a little less punch in the higher revs. Not a big difference, but enough that I keep my YICS hooked up.

If you want to try something, connect the hose from #2 to the nipple on the cyl. head for #1 (the hose isn't quite long enough to reach, you have to jury rig a slight extension). And do the same on the other side...connect the hose from #3 to #4 YICS cyl. head nipple ( I think this side fits with no extension).

Also known as "the Jason Mod". It will idle kind of funny, but throttle response and low end torque will be, well, better. How much better depends on how well you bike is tuned.

[fixit3546]

Randy, I thiink it has something to do with stabilizing the vaccume on the cylinders. I could be wrong.

 

I had the jason mod on mine for a while; but i put it back on the YICS a couple of weeks ago because i need to "Sync my carbs" and you cant do that with the Jason Mod so i'm told. I might get around to doing the sync some day.

 

I cant tell much difference with the Jason mod; but it sure sounds better (at idle) with it.

[Denden]

Here's what is in the Yamaha Service Manual...

[bongobobny]

As Denden pointed out, it promotes the "Bell effect" on the intake cycle which improves ignition and gives a more thorough and efficient explosion. The Bell effect comes into play more pronounced at higher RPM's so you won't notice any effect at idle, but it does add to the top end and increases eficiency...

[Gearhead]

Why did Yamaha eliminate it on the 1300 motor in 86 and up? Cost? Or did the redesign the intake port to achieve swirl without YICS?

 

Jeremy