Throw Away Your YICS

[PeteXS/GS/CB/XZ]

I didn't think I would say this, but the YICS is useless.  My '82 was hanging up at higher rpm and wouldn't come down to a nice idle quickly enough.  We finally determined it was the YICS, which was fubar from a previous owner(s)and must be leaking.  We blocked the hoses from the motor to it and this Vision ran perfectly.  I didn't think you could outthink a team of Yamaha engineers but I guess this is an instance where EPA emissions technology was still primitive.

By the way, the bike sounds really good with its Spec II pipes and should be a strong runner once we get enough gas to the rear carb (the pilot jet was replaced but something else must be plugged).

[Lucky]

So your saying that because it was not functioning, the bike ran bad, and once you removed it it ran better, so throw it away? and you don't think it might run even better with it fixed?

ok, I know I'm new here, but really?...

[PeteXS/GS/CB/XZ]

Yes, I can't see how reinstalling it even if repaired will improve anything.  It carburetes very nicely now.  Uh, Lucky, I know you're not exactly a newbie:)

[Lucky]

My point is that there are two schools of thought on the subject & to advise everyone to just throw it away is irresponsible.  the science behind it is sound, more likely your machine is out of tune and/or needs a valve adjustment. you might be used to the way it runs & not realise what your missing.  my Visions run like their asses are on fire..

[lexx790]

I don't know which side of the fence I stand on this, I took mine off and replaced them with 1 foot long tube capped at the ends.
It seemed to work ok with my repaired YICS to start with, then it leaked, so I replaced it with some tubes and it seems to work okay again.

[The Prophet of Doom]

Lucky is right.  The value of introducing swirl to the combustion chamber is very well established.  That's what the YICS does although there are now other methods of doing this.
The primary purpose is NOT to increase power, but to improve economy and reduce emissions through a more complete, progressive burn in the combustion chamber.  Just because you do not notice a power improvement from the YICS does not mean it is not working.  I've tried both working YICS and blanked off (not forgetting to adjust idle, mix and sync) and got almost 50km extra distance per tank.  That's nothing to scoff at with today's fuel prices. I also believe it runs better, but there are lots of variables - fuel quality, temperature, air pressure that make it hard to tell without scientific measuring

If you only have a choice between a broken YICS and blanking, then blanking is far preferable.  If you have the choice of a working YICS and blanking, then the YICS is  preferable

[YellowJacket!]

My Vision starts and runs much better with a working YICS.  Since I know it works well with a working YICS, if I take it off and cap the plugs, it runs and starts like crap.

David

[Hartless]

this is a topic that i have been going over in my head for the past couple weeks. i repaired the yics when i first purchased my bike , amd it did not seem to do much , i then repaired /replaced the tube going to the yics and that made a little bit of a difference  with idle and rev. i then capped them off and it runs a lot better. now i may have not repaired the yics box correctly , but i still do not see the logic in it in the first place. it seems to me that when you cap it off , the same things are happening , one sucks , one blow ( quit it you pervs) . correct me if im wrong ,and i know i probably am, but thats what it seems to me.
i think now i am going to search the net and see what the yics really does and what the thought process is. i see that someone said swirl , but i do not see how that is possible with the yics box ???

[Lucky]

i think now i am going to search the net and see what the yics really does and what the thought process is.

Read the first few pages of the Yamaha service manual

[Hartless]

haynes or yamaha.... all i have is the haynes

[Lucky]

Yamaha

[Hartless]

awww bloody hell. guess i wont lol. i think i will rebuild one the right way( ive aquired a couple) and see how it works

[PeteXS/GS/CB/XZ]

As I've said before, I'm reluctant to try to outthink a team of Japanese engineers but I still can't see the advantage of a working YICS.  I repaired mine where it was leaking at the screws but the bike seems to run beautifully without it.  (I did have a leaking cover on the accelerator pump, which has been repaired.)  I will give you a full report once I finally ride this bike.  All I can say at this point is that it starts, idles and runs beautifully on the repair stand.  It has had new carb kits installed.

As for the swirl feature supposedly supplied by the YICS, I would think any four-valve head like that in the Vision has plenty of swirl and turbulence and flow.  This was the strongest 550 of its era afterall, which is saying a lot when the competition then was the formidable Kawasaki GpZ550 which smoked plenty of Honda 750s.   Then the basic engine configuration was simply doubled to make the killer VMax.  On another subject, maybe VMax carbs are the ones we all should have installed all along (I mean half a set). 

[Night Vision]

I have a vision that wants the YICS... another that doesn't.. but the "doesn't" has predator exhaust and is highly re-jetted..

the only way to tell for sure what they want is to have a working YICS and try it both ways... 

[Rikugun]

the only way to tell for sure what they want is to have a working YICS and try it both ways... 

I'd add to that.  As Lucky was talking about earlier, the bike needs to be in the proper state of tune, including (or especially) clean carbs. Otherwise, the addition or deletion of the YICS may be adding to, or masking a pre-existing condition caused by something else.

[Lucky]

Plus, i suspect many repaired YICS's are not actually completely repaired. the water test is the only sure check...

[PeteXS/GS/CB/XZ]

And mine has a Spec II exhaust, which is partly why I bought.  I know Gary and respect his work with RD350/400s, the RZ350 and the Kawi H1s and H2s.  Maybe a good, uncorked exhaust is the reason why my Vision doesn't seem to need the YICS. 

[Lucky]

Gary Wolf made Gary Wolf Exhausts.. not Spec II's. that was a totaly different company...  Gary Wolf is a musician, & his motivation with the exhaust was to tune them to perform with the bike & get a certaim sound quality at the same time.

[Walt_M.]

I have Spec IIs on my '83. I put them on in '86 when my originals rotted out. No jetting changes and I still have my YICS, runs great.

[jasonm.]

I use a vacuum tool....Mighty vac to check YICS.  I can tell anyone that the YICS does work well when NOT leaking. Bike starts easier, carbs better at lower than 4000rpm and the engine gains 200 rpm at idle with it vs. w/o it. Anyone want to send me the YICS units they don't want...? I know I can fix them. And then sell them to someone who appreciates a proper running 'cycle.