I am traveling down the same road as Bill in that I am bringing an '86
Venture up to Max specs. There is more in common between the two motors
than there are differences. Their origin is the same, and it is useful to
take a look at old road tests. One obtains clues as to the "whys" of Yamaha
engineering - particularly why some modifications work and others don't. In
the June '83 Cycle road test of the first Venture the writer states that the
seed for the motor began seven years before.
"Now, a short history lesson. Several years ago, in 1975, Yamaha began
work on a (sic) European endurance racer powered by a non-counterbalanced
90-degree V-four. This machine led the way to the 550cc Vision, which
essentially was the endurance racer sawed in half lengthwise, with added
counterbalancer and its V-angle tightened to 70 degrees. It shared the
racer's narrow valve angle, downdraft carburetion and liquid cooling. It
even had the racer's frame layout. Then, two years ago, Yamaha launched the
V-four Venture project.
The new V-four isn't a Double Vision; there are too many design
departures for that. Examples: the Venture's crankcases split horizontally,
the Vision's part vertically; the Venture's cylinders are molded integrally
into the crankcase casting, the Vision has separate cylinder blocks; the
Venture's 76x66mm bore and stroke differ radically from the 80x55mm Vision
proportions.
Despite these departures, a marked similarity remains in certain areas,
enough to stamp the signature of the same engineering group on both engines.
Like the Vision's the Venture's cylinder head has offset inlet ports. In
this system, one intake valve lies at the end of the curved inlet port; its
mate gets a straighter shot from the carburetor. The offset "masked" valve
gets the YICS (Yamaha Induction Control System): a small feeder tube,
sitting just upstream from the valve head, squirts extra fuel/air mix from a
separate plenum chamber and creates a swirl to increase combustion
efficiency.
A concern for charging and combustion efficiency is also found in the
gernal design of the cylinder head. The Venture uses a narrow 35-degree
included valve angle (one degree narrower than the Vision's), which results
in an extremely compact combustion chamber. Thanks to a shallow chamber
roof, tall pent-shaped pistons aren't necessary; although flat-topped, the
pistons pump compression to 10.5:1. A flat piston top encourages good
cylinder filling when the inlet valves are barely off their seats. A
compact chamber, moreover, allows fast flame-front travel during combustion,
which not only helps power but also reduces exhaust emissions."
Joe Minton wrote for Rider magazine in May 1983:
"There are four swirl-inducing Y.I.C.S. chambers that feed a high velocity
stream of mixture to each intake port as the valve opens. These small
chamber are not inter-connected as with some other Yamahas because, I
suppose, of the uneven firing order of the V-engine. The U.I.C.S. units are
maintenance are except for the connecting hoses. Yamaha claims improved
fuel mileage and power from this design feature."
Seems to me that the Y.I.C.S. chambers must have a fuel/air source from the
carburetors. I think Bill is on to something here. Maybe the design was
dropped from the Max because of cost and the feeling that the Max had
"enough" power.
It would be interesting to see a dyno sheet from Bill's motor with and
without the Y.I.C.S. It may well be that the absence of Y.I.C.S. is part of
the reason for the troublesome mid-range flat spot in Max motors.
Rey Kirkman
----- Original Message -----
From: Bill D. Miller <[EMAIL PROTECTED]>
To: V-MAX TECH LIST <[EMAIL PROTECTED]>
Sent: Sunday, April 09, 2000 7:48 AM
Subject: Yamaha CICS
> Here's a problem one of you VMaxers may be able to solve: early ('83-'85?)
> Ventures used a CICS "system" comprised of a 3"x12" plastic box with four
> sealed chambers; each of which was plumbed into the intake port of one
> cylinder via a rubber hose (look carefully at your VMax cylinder head
> castings and you'll find vestigial bosses near each port). The chambers
> evidently acted as vacuum reservoirs -- but I can't imagine why they were
> needed or what, if anything, they did. There is no direct connection to
the
> carburetors (other than through the intake port) but I can run the Venture
> with a wide open airbox and it seems to experience none of the usual CV
> carburetor problems (coughing, bogging, excessive leaness). In fairness,
it
> has been suggested that the explanation for this phenomenon is size of the
> early Venture pilot jets (42.5), so maybe it's not related to the CICS.
>
> The Service Manual offers no description of the operation of the CICS --
and
> provides no service guidance. Just another cute 80's acronym to sell
bikes?
>
> I'm mounting 1985 VMax heads & vboost on a 1300cc Venture motor (for
> installation in my '83 Venture) and wonder if drilling those bosses and
> remounting the CICS would improve/detract/not affect performance. I'll be
> using the VMax flywheel and pickups with the '83's ignitor unit. Your
> comments would be appreciated -- but I subscribe to the digest so won't be
> able to reply to any questions 'til the next day unless you want to
contact
> me off list.
>
> TIA
>
> Bill Miller
>
>
>
> .............................................
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