Can anyone explain to me, in detail, what the YICS system is for on my xj 700 and how it operates.
Thanks
Mike

If you have a Haynes manual, it's on page 127, section 9. It is is a passage drilled across the back of the engine case, just below the inlet ports. Then there are smaller connecting passages from this main passage, with each connecting passage emptying into the respective cylinder just before the intake valve. When any cylinder is on the induction (intake) stroke, the small passage is subject to high depression, which causes air to be sucked through it at a greater velocity. Because of this high depression, some of the air/fuel mixture in the other passages is also sucked in, along with some additional mixture coming from the other three carbs. This concentrated mixture enters the cylinder in a swirling manner, which improves combustion and thus increases horsepower.

In effect, this is similar to Ram Air on the old Pontiacs or the induction systems used on older Chevy's and Fords. Basically, it scavenges mixture from the other cylinders and the carbs and gets more mixture into the cylinder that is about to fire, then repeats the process for the next cylinder. In this manner, the cylinder that is about to fire has the optimum fuel/air mixture and you don't loose so much unspent mixture out the other exhaust ports. Hope this helps.

I Have not been able to find a haynes on this bike but was recently informed it was the same as a 750.
I am concerned about the YICS system for syncing the carbs. Would this system also compensate for an out of sync carb on the bike?
I am having minor problems with my 700 and trying to track down the gremlins.
Thanks for your help.
Mike

I was also concerned about syncing my carbs without a YICS, but I gave it a try without the YICS - guess what - it worked great. My bike idles smooth as glass. The YICS tool is definitely not needed to effectively sync the carbs, though it may make the job a bit easier.

I agree, you can synch the carbs without the special tool almost as well as with it.

An advantage of having the tool is that because it isolates the carbs, it can help you determine if one of the carbs is not working as well as the others. If the carbs aren't isolated, the weak carb can be compensated by the stronger ones.