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Discussion Starter #1 (Edited)
I just tried out this new vacuum hose mod that smooths out the low end, which I got from the french Kawette forum: http://www.kawette.net/forum/viewtopic.php?t=19314
The IAP (Inlet Air Pressure) sensor has a hose on the left throttle body. The mod consists of a hose that connects both TB's at the carb synch fittings with the IAP hose coupled to the connector hose. This smooths out the IAP reading and balances out the vacuum pulse between the two TB's. Kawette forum got the idea from an Italian source, and they tried two other connecting methods with additional routes but with the same results... A smoother response at low rpm range without hiccups is noticed, as well as improved tractability, torque and throttle control. Some reported better fuel economy. Engine braking also seems to be reduced.
I really like the improvement so far. :thumb:

UPDATE: (post # 134 on page 7) After noticing that the IAP sensor fitting bore is larger than the two TB vacuum access fittings, I tried connecting the left tube on the smaller vacuum access fitting instead of on the IAP fitting, still with a T and the right tube on the other TB's vacuum access fitting. I had to raise idle rpm back up and it ran very poorly and sounded erratic. I pulled over and quickly put it back like I had it with the left hose on the TB's IAP fitting... I then put the IAP hose back on its fitting and connected both TB's without the T. It's also known as configuration '1' in the french forum, as some have reverted to. It runs at least as well now as with the left hose on IAP fitting and a T like I had it. I'd like to try out configuration '2' now, as shown in second pic... I had enough 5/32" (3.83 mm) vacuum hose to replace the thin, slightly short and bent IAP 6 mm hose as well. I was able to do it all in a few minutes with a slim pair of needle nose pliers.

The best and most simple configuration #1, with a single 6" (15 cm) long 1/8 or 5/32" (3mm) ID vacuum hose on both TB vacuum ports. Leave the left outer IAP hose alone, and forget about using a T:

 

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Geez, there are tons and tons of members at that forum! I can't read French enough for real comprehension, but certainly this question has been asked.

There has to be a reason why this wasn't done on the stock bike... maybe they thought the cost of carrying 3 lengths of hose vs. 1 and 1 t-junction was too high.

Furthermore, does any other bike (specifically : more expensive) have this sensor hose attached to more than one TB?
 

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Discussion Starter #3
I've been wondering the same thing, and what effect coupling the TB's on a non-FI twin would have... Cars read IAP at the intake manifold which has all the intake inlets together on a common chamber.
This mod stabilizes the IAP signal, by reducing the vaccum pulse width and by doubling its frequency.
 

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A quick question gents: What is blank plate with two bolts on it? It sits centerline of the valve cover between those two electrical connectors.

Red
 

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Red alert, I think that the aluminum plate you see is Invader's PAIR valve block plate. It's another mod that will keep an aftermarket exhaust from popping on decelleration. It seals the port that usually gets air from the PAIR valve to keep it from entering the exhaust.

For more info try a search on the forum for PAIR valve.
 

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Discussion Starter #10 (Edited)
No, it's nothing exotic... I just got one foot of available 1/8" (3mm) ID vinyl primer hose and a white plastic T from my Yamaha dealer. It works fine, but I'd like to get some nice silicon tubing.

PS: I then upgraded to 3/32" Goodyear vacuum tubing with a 3/32" T fitting.
 

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No, it's nothing exotic... I just got one foot of available 1/8" (3mm) ID vinyl primer hose and a white plastic T from my Yamaha dealer. It works fine, but I'd like to get some nice silicon tubing.
Silicone tubing will deteriorate on contact with gasoline and/or gasoline vapors...don't ask me how I know that! I know there shouldn't be liquid gasoline in these tubes, but when you shut the engine off, the vapor may creep up into them. There is a chemical resistance which also shows gasoline in contact with silicone as a "No" here:

http://www.watson-marlow.com/wmb-gb/p-chem-g.htm

You'd probably be best off just to use some regular automotive vacuum hose. It should handle any gas vapors fine, and it would color match with the original hose. Throw in a brass 'T' or 'Y' fitting if you want a really fancy and bullet proof set-up.
 

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Discussion Starter #14 (Edited)
Thanks for the info on silicone tubing... A brass T fitting wasn't available then. The white 'plastic' one is light but fragile. Tygon tubing as used in RC is usually available in bright colors, but would be good and very flexible.
I'd like to try polyurethane tubing (available in transparent or opaque colors), also much better than regular rubber automotive vaccum hose with it's high resistance to oils, greases, fuels, vacuum, weathering, abrasion, tearing, pressure, impact, radiation, prolonged or frequent flexing, good tensile strength and high elastic memory. I could also upgrade the existing IAP sensor tube.
 

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I have a spool of the tygon stuff and have been using it for a long time on my gas RC planes, and while it is good, it does deteriorate (harden) and would certainly need to be replaced every two years or so.
 

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I have a spool of the tygon stuff and have been using it for a long time on my gas RC planes, and while it is good, it does deteriorate (harden) and would certainly need to be replaced every two years or so.
Strangely enough, I used to use silicone for my 'gas' RC planes and cars...it seems to hold up well to the nitromethane, methanol and castor oil mix that they burned. But only lasted a few hours in gasoline! Go figure~!
 

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You never know what's in gasoline these days!!!
 

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Did this mod on my V. today. After riding around about 200 miles, A couple of things I noticed. After getting my exhaust, I noticed it seemed to take a bit more throttle to get me going smoothly from a stop, and sometimes it did not go so smoothly!!! After doing this mod, she seems to pull away much cleaner and with less effort. Seems to be a little smoother at low speeds as well, not that this was ever a major issue. Kinda feels like she pulls a bit easier with given throttle application as well. Whether I have gained any hp, I can't say, but I assume torque has improved a bit down low due to the easier starting. My mileage last fill up today returned about 60 mpg, with a few wheelies and a top speed pull. :yeahsmile:I'll report on mileage again if it has improved with normal day to day running. The mod took about an hour to perform, very easy, and cost me about $5 in parts from local auto store-1.5 ft 1/8" vacuum tubing (of which I have about 10" left over), and one 5/32" (3.96mm) vacuum tee. Till then, here are a couple of pics of my install. Thanks a bunch, Invader, for the info!!!:thumb::thumb:
Fukken cheers,
Erik!!!
 

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