Interesting YICS experiment

[skucera]

At the end of last summer my bike was running a little uneven, so yesterday I figured I would look for vacuum leaks, and I found a small one.  One of the vacuum caps on the YICS inlet on one of the cylinder heads was cracked, so I replaced it with a new vacuum cap and the bike smoothed out quite a bit.  It was also easier to start, and idled back more evenly again too.

Encouraged by that easy success, I wondered if the YICS canister was leaking, since that is the most common reason folks here list in YICS threads for bypassing them.  I took mine off, and it looked perfect, with no obvious cracks.  I tested it with my Mityvac, and sure enough it wasn't holding vacuum.  I figured I could test it better if I applied pressure to it in a bowl of water, and sure enough I found it leaking in only two spots, the two screw holes at the upper corners.  Hmmm... I figured I could plug those wholes with some Hylomar on the screw threads in those holes, so I tried it again in the bowl of water and no bubbles.

I then pulled the vacuum caps off, stretched some new vacuum hose from the YICS nipples on the heads to the place the canister bolts on, snipped them, and pushed them on.  Well, my hose was not a tight fit on the canister end, so I found some hose clamps, pulled the hoses off the nipples on the heads, clamped the hoses to the YICS canister, then routed them through and connected them to the heads.  I started it up even better, and idled even more smoothly.

I took the bike to work today, a 40 mile round-trip, and it really runs nicely now, nicer than it has ever run since I bought the bike.  The low end torque is noticeably better.  The top end power seems exactly the same.  So, for something so many people say is worthless, it sure seems like the Yamaha engineers knew what they were doing.  ;D

Scott

[George R. Young]

So, does the non-leaking YICS work better than simply capping the nipples?

Or is it simply a complicated nipple cap?

[skucera]

George,

Yeah, it does work better.  I used some translucent silicone hose I picked up in the bargain bin at my local auto parts store a couple of years ago, and when the choke is set it is amazing how easy it is to see the pulses of fuel and air that jump back and forth in the hoses to the YICS gadget.  I was surprised.  With the choke closed, the hoses don't show anything moving back and forth, but after two days they are starting to turn a golden color from heat and hydrocarbons or something.

I'll let you know if I get better fuel economy.  With the vacuum leak at the end of last summer my fuel economy was down to 40 mpg, so there was certainly room for improvement in efficiency, considering I have 18.9 miles each way to work and only about 2 miles in city traffic.

Scott

[turbosteve84]

Yeah, those two screws on the top corners of the YICS box tend to loosen up.

I resealed a box using SuzukiBond (ThreeBond black, 1207B) over a year ago. Back in early April when the bike started to stumble off idle I immediately suspected the bonding agent had failed. Nope. The screws had just loosened up a bit -- enough to cause a minor leak. Tightened the screws and away we go. The SuzukiBond is still holding. Good stuff.

Oh yeah, you can easily feel the YICS hoses pulsating between your thumb and forefinger. I can't say the Yamaha engineers "knew what they were doing" when they designed the YICS since it's so prone to failure, but the science seems to be sound. I'm still getting lousy fuel mileage though (approx. 35 mpg US).

I have since bought another box via eBay and resealed that one with SuzukiBond, too. Just in case the bond should fail I have a backup that should last a couple of years (at least). Two minute swap and I'm on the road again.

Steve

[skucera]

That "prone to failure" idea is one that Japanese motorcycle companies in the Seventies might think of as odd.  They were trying to capture buyers who bought the newest, fastest, latest thing all through the Seventies.  They really didn't figure that anyone would keep one of their motorcycles longer than a year or two, and the YICS canisters lasted that long, and even longer.  Ten years, perhaps they could last that long... 20 years... 35 years... that length of time was well outside their design parameters....

As for wanting to use swirl in the combustion chamber, well, that was being researched and sold in lots of cars and motorcycles.  Cars had room for stratified charge, like Honda's CVCC with its third intake valve and richer mixture introduced into its own little pocket, to come swirling out past the spark plug at just the right moment to ignite the very lean mixture in the remainder of the combustion chamber.  Yamaha had YICS.  Jaguar came out with the May Fireball head that greatly increased power and efficiency of their V-12, which was originally designed for top end power, not efficiency.  Yamaha was on the leading edge with this stuff back in the late-Seventies when they came out with YICS.

Nowadays, engine designers have the benefit of really fast computational fluid dynamics, and from what I've ready almost all engine designers around the world use the full benefit of their super computers to design engines that fill very efficiently, with turbulent swirl around their many valves and computer designed intake tracts.  They even use the fuel injection spray patterns to cool the charge in the combustion chamber using direct injection.  Very cool.

Scott

[turbosteve84]

"Prone to failure" is not an "idea." It's a fact. I can't picture Yamaha execs sitting around a table saying "just make it last a year or two." If that was the case, why is the engine designed to last for so long? The Japanese didn't put Triumph (resurrected!) BSA, etc. in their graves (and bring Harley to their knees) by building bikes that lasted 24 months.

I think the Tuning Fork guys just dropped the ball on this YICS thing. Maybe that's why we don't see a similar setup on modern Yamahas. Instead of improving it, they probably just figured it wasn't worth the effort, since making a unit that didn't leak isn't that much of a lift. Remember, they introduced 5-valve heads but later abandoned it, albeit for a different reason. The supposed advantage didn't outweigh the cost, and from a marketing view it had lost its cache.

Just my opinion.

Steve

[Rikugun]

It's not the execs job to decide on such minutiae but they are responsible for putting pressure on all departments to maximize profit. Somewhere along the way compromises are made on the quality of components. The engine and powertrain may be designed for a long life but that's not to say many components on the bike are sourced with a price that reflects a given failure rate.

Acme Manufacturing LTD. takes a  meeting with a Tuning Fork purchasing manager and together they work out a deal for regulators with a failure rate of X/1000. This represents a 21% savings compared to those with a lesser failure rate simply by using a lesser quality diode type. Tuning Fork purchasing manager's bosses approve the deal and get a bonus at years end. The purchasing manager gets to keep his job and Tuning Fork company gets to sell more replacement regulators keeping the parts department end of the business in the red. Everyone is happy. It's the classic win win scenario.

[QBS]

Never forget the misdirected oil seal in the starter, or the incompatible metals in the reg/rec stator coil connector.  Whats with that?

[skucera]

Well, if it's like the company I work for, the minor stuff is given to the junior engineers fresh out of college, while the important stuff is done by the experienced engineers and the stars on the engineering staff.  They all get annoyed at the marketing managers who decide to cut corners by employing cheaper components or dropping features to bring the price point down... but the engineers get the product designed and tested and released anyway.  I imagine that the choice to go with non-adjustable forks without air pre-load was just such a marketing choice, because the price was already rather high compared to the Kaw GPz550, for example, which had air pre-load.  Minor stuff like starter oil seals could well have been handed off the a young engineer, and incompatible metals are a rookie mistake, but it depends on the presence of water or salt air... or time... to make a problem like that really bad.

Scott