Carb tuning and deactivating YICS

Started by hoverhead47, March 07, 2015, 07:23:25 AM

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I've just read a treatise claiming that to tune and balance Yamahas 1982 and newer, the YICS needs to be deactivated.  This article IS referring to the inline engines but I am wondering if the same may apply to the Vtwin.
Here is item
Any opinions (considered preferably)?

The Prophet of Doom

The YICS on the XZ is very different - there is no linking between the cylinders so there's no need to disable the YICS to balance.


Absolutely correct. Not only that, the inline fours have a special YICS tool -- kind of like a long, metal stick --  you use to close off the system. Try finding a mechanic who still has one of those. MacGyver types make their own.


The YICS is different but back when I had XJs I had the same problem finding a tool.

I didn't want to use a MacGyver version of the tool. I made one. Local shop owner let me get dimensions from the tool in their shop.

This probably isn't news but the YICS ports obviously impact vacuum for the fuel pump. Yesterday while working on the startup of my XZ after storage and a carb rebuild it started and idled fine. It backfired once then would not start. The backfire blew the cap I had put on the YICS port on the front cylinder: the result was  insufficient vacuum for the fuel pump.
- Mike O
1982 Yamaha XZ550RJ

fret not

Retired, on the downhill slide. . . . . . . . still feels like going uphill!


Thanks. I manufactured them for a while. Sold about 400 of the all over the world.

Then some guy bought one, copied the measurements from it then had some job shop in China start making them.

Of course I wouldn't match the price so I stopped making them.
- Mike O
1982 Yamaha XZ550RJ