yics?

what is yics? does it make the carbs hard to tune?

 

Yamaha Induction Control System. A system of passages connecting intakes in the cylinder head.

Yes, if you don't have the proper tools. No, if you do.

 

It's all right here.

 

Vyper,

What they^ said and just for clarification the top diagram in BF's post would be you looking at the yics passage and the valves from the bottom of the head. The blue air-fuel mixture is coming into the head through the manifold boots. Hope this helps.

Gary

 

big fitz never ceases to amaze, i mean wow, must have a phd in xj's, i looked on this post to see what kind of responses there would be and before anyone could say something silly........ a diagram, hats off big fitz

 

Fitz

I like your diagram but am somewhat skeptical about the advantages of the YICS.

Looking at the air path within the system has me scratching my head. The air being supplied to the cylinder that is on the intake stroke is pulled from the other intake tracts. The smallest orifice in this air path in a 2mm hole between the head and cylinder castings (ref 750cc motor).

With a closed throttle if the manifold vacuum is say 15”hg the cfm being pulled thru a 2mm hole is around .6 cfm. At open throttle the manifold vacuum would be considerably less than this and the low differential pressure between the manifold tract of the pulling cylinder and the remaining manifold tracts would provide less cfm thru the YICS path.

My thinking is that when you need the YICS swirl in the combustion chamber to make power this coincides precisely when the differential pressure in the system is low and thus the advantage is reduced. And that the volume of air that can pass thru the 2mm orifice is so small that any swirl would be obliterated by basic turbulence.

I am definitely thinking I am missing something fundamental in this thinking. Perhaps the differential pressure between the exit port just in front of the valve and the restricting 2mm port is greater than the general manifold vacuum.

Need to think about this one.

FlyGp

 

Check out the link posted by biggs500. Chacal does a good job describing it exactly how Yamaha pitched it. You can decide the validity for yourself.

 

required reading for yamanuts.
yics on page 88
yamaha history

 

It's not "my" diagram. It's Yamaha's from early promotional literature when they came up with it.

I suspect it has more effect, performance-wise, in the 550s, due to the size of the YICS passages in relation to the size of the intake tracts.

Yamaha seemed to think it worked; they put an awful lot of effort into it. Knowing their track record, I can't imagine they would have stuck with it as long as they did if it was ineffective.

However, it may have been an EMISSIONS "band-aid" more than anything else; and they needed to sell it to us.

 

I don't see where it provides a performance advantage over other makes. I remember the sales pitch when it came out and though it more a clever marketing ploy than anything. But fitz may be onto something about the whole emissions tilt.

 

They (Yamaha) incorporated it into many models - - the Vision 550, the 1200 Venture, the 400 XS-XJ - - and there was NO YICS tool for these models, (for the carb sync)

I think they did it to secure the patent on the whole "port swirl" invention.

And yes - on the "shafties" - the ports are restricted to a 2MM hole.

 

suzuki had something called TSCC with their four valve heads but they didn't have that magic 2mm hole everyone makes such a big deal over

 

You can get a swirl effect by the port entry angle into the combustion chamber. If memory serves me correct one of the major manufactures used this technique to some success. And let's not forget the radial head design on the honda singles. A design I might add that added complexity to valve actuation without much benefits imo.

 

Way back, just around the time history started to get recorded, I was an apprentice mechanic for a Honda-DATSUN dealer. I seem to remember that the Honda CVCC (which was the "Bee Knees") was similar in design.