YICS - not again?

[madmax-im]

Ok Guys Not to worry

Hey we will get this taken care of one way or another...so it may be a bit of a PITA compared to earlier engines...just my luck...but I'll be ....if I ever thought I'd see the day where Max sat stripped down in my garage and me doing the work with the good help of a fellow XSive..Randy...

[trbig]

Hopefully a pic or 3 will say a thousand words... so I don't have to.


YICS = Yamaha Induction Control System

The '82 does indeed have an altered head and cylinders versus the XS. There is a tube on the back of the cylinders with ports that interconnect all the carbs. These help to make the bike run better by letting a carb "Borrow" from another carb if one isn't exactly up to snuff.



In this pic, the bottom head is a '78 and the top one is the '82 and you can see where the ports in the head match the holes in the tube on the cylinders, and see that the '78 is missing these ports. I should have turned them the same way.. sorry. You can also see the difference in exhaust stud lengths that someone talked about in a recent exhaust thread.



I don't know if you can see the hole in the top in this pic or not, but this is inside of one of the YICS ports in the head. Each of the ports has this hole at the top.



I don't have a pic of it, but this hole leads directly into the intake chamber right in front of the intake valve.


So in theory, this SHOULD help the XJ still run decent even if the carbs are out of synch quite a bit. You won't get all the power you should, but if an XS and an XJ had equally un-synched carbs, the XJ should run smoother. One bad carb will throw off an emmision test and this was designed to help that. A lot of people want each carb functioning correctly and want to know when it's not, so the YICS gets blocked.

Not sure of the name, but I tapped the ports on the head and screwed in one of these allen plugs in each one.






Has worked well so far.

Tod

See there.. only 999 words!

[Axel]

YICS

Nice post . Now I know something !

[madmax-im]

Thanks Tod...that really explained it so even I could understand ...LOL.

[Axel]

YICS plugged

Is it really worth it to plug the YICS system ?

[MacMcMacmac]

YICS is designed to impart swirl to the fuel/air charge by admitting a high-speed jet of air/fuel from the other carburetors into the cylinder to promote swirling of the mixture, and thereby achieve better fuel/air mixing inside the combustion chamber. Yamaha claimed as much as 10% better fuel economy, and probably more power, but considering it dropped the system entirely in the mid 80's, it couldn't have been doing much. 5-valve technology probably rendered any YICS-derived benefits moot.

I plugged the YICS system on my Seca turbo with simple cloth rags tamped in with a metal rod. Others have used rubber hoses swollen out with compressed air. I have even heard of people using corks.

[trbig]

Hmmm.... Considering that the XJ was supposedly the slowest of the group, it doesn't seem to stand up to the claim, does it?


Tod

[MacMcMacmac]

Of course, by plugging, I meant for carb balancing, not plugging permanently.

[Axel]

YICS a conspiracy

Maybe they were looking for a reason to put some cool looking letters on the valve cover and get the people to buy the new bikes

[randy]

Ok, one last question. What is the thread size of the YICS access port in the left side of the head?

Thanks

[trbig]

I just pulled one out, and it looks to be a 12mm bolt with 12mm fine threads (1.25mm) by @ 21mm long. Maybe someone will chime in for sure, that's just what the caliper reads.

Tod

[randy]

Thanks, Tod