A cracking FAQ/'How to' by TLRMAN (Mark)....first off though, some extracts from the manual:

Refer to the Service Manual, Chapter 4 - FI System

By TLRMAN July 2005:

Introduction to STVs

Well, it's a long time coming, with me having to move to a new residence and such but I promised AndyW I'd get the job done.

Secondary throttle valves....There are many thoughts on just what the heck they do. Some say it's for noise abatement, others think they just get in the way and affect the true performance of the bike and some would just rather remove them.

I should point you in the direction of my tech article about Carburetors.
More directed to the "Constant Velocity" type.

Since the introduction of fuel injection, we no longer require a pressure drop through a ventury to pull fuel from a fuel bowl, and introduce it into the engine. We have a fuel pump that sends pressurized fuel to fuel injectors, and thanks to IC chips, and sensors, we can spray the fuel into the engine. No need for fancy needle jets, main jets, primary jets, and airbleed jets. Never mind making sure the fuel level in the carb bowls is the correct height.

There is one thing that's important with the CV carburetor and that's how it keeps the air velocity constant through the intake ports regardless of throttle position. If you ever had flat slide carbs, and immediately opened the throttle, you would notice that the engine would take a big gulp of air, and hesitate, or even stall. Accelerator pumps were introduced to keep this in check. So, in regards to keeping air velocities constant especially at lower engine rpms, one concept for a fuel injected engine is to add separately controlled throttle plates that can move independently from the main throttle plates. This way, if the throttle plates are opened quickly, air velocity will drop, but with the Secondary Throttle plates lagging just behind, can keep the air velocity up, and help with atomization of the fuel injected into the engine. of course if you are racing the bike, and it never sees rpms below 6 to 7,000 rpms, there is no sense on having the secondary throttle plates there, and can be removed for some added increase of air. Most of us don't race, and use the engine through a wide range of rpms, and with the STV's installed really doesn't detract from performance, but keeps it more tractable.

Now, enough said about how they work, lets see how we adjust them.

STV Adjustment

Maui, aka (Dave), was kind enough to donate his bike, (and get some free work done) by yours truly.

We first started to check his Throttle Position Sensor (TPS)... (see Chewy's killer Tech tip) and found that we needed to make a small adjustment.

After that was all and done, we had a look at the STV's.
There are basically 3 parts to this arrangement.
1. The STV's.
2. The servo motor that drives them.
3. The STV position sensor that tells the ECU where they are in position.

First thing to do is raise the tank, and remove the airbox assembly. Those Pair valve hoses are a BITCH! (Hint Dave...Loose the pair..)
There are several connectors that need to be uncoupled to facilitate the removal. Just remember where they go, once you tend to the task at hand.

First thing to identify, is the STV's it's kind of a no brainer, but we want to cover everything...This is pic #1

Next is the servo mechanism, pic #2

And finally the STV position sensor pic #3

We now want to find the connector at the STV position sensor, the wire loom is actually folded and tied together. pic #4.

We next want to identify 2 wires that are part of the connector at the STV position sensor...These will be the Black and Yellow ones. There are 3 wires but we are just interested in the black and yellow ones.

You will also need a test meter, with a way to check impedance/resistance (ohms).
First disconnect the connector and find the 2 wires.

Next is to find the STV servo and on the very end you will find a shaft that you can turn that opens or closes the STV's....

NOTE, DO NOT TURN ON THE IGNITION AT THIS POINT!
There is a voltage check that can be performed for trouble shooting with the connector plugged into the STV sensor but we are more concerned with the resistance.

First step is to turn the shaft, and close the STV's.

We then use the meter, and check the resistance across the yellow and black wires. It should be in the range of .58 Kohms. We found that Daves was out of spec.

Next, is to turn the shaft on the STV servo the opposite direction and fully open the STV's. Carry out the same metering, between the 2 wires. At this point we found that the STV open position relative to the STV sensor was out of tolerance and should be in the range of 4.38 Kohms.

We then unscrewed the set screws on the STV sensor, just loose enough to allow some resistance when turning the sensor....(safety torx as usual), you must purchase a set!

As I turned the sensor, I had Dave reading the Ohm meter, and calling out the numbers. We found that we had to settle in between the set range, but was still a lot closer than when we started. This was checking open STV's versus closed.

Once we agreed that we were in the range specified, we buttoned up the bike, and sent Dave on a little test spin. Dave came back and noticed there was more of a response in the low to upper midrange of the engine and overall was a happy camper. I also got to rip the snorkle out of his airbox with one good tug!

This day didn't actually go uneventful because Dave tried to kill my TLR but that's another story.....

Usual disclaimers apply guys so take care!

Question and answers:

Q  Originally Posted by chewy22
So what you are saying here is you may need to make a slight adjustment to get the best out of them. We are looking for resistance outputs in the fully open and closed to be in the range given above.
If my understanding is correct here Dave’s bike used as the guinea pig were not fully opening and closing when required to
Or they were but just sending the wrong (RESISTANCE OUTPUT) signal to the ECU.
And if not then slacken the pot and turn into the correct position to meet the specifications given by Suzuki, a little like the TPS settings.

A  There is actually a little slop in the worm drive of the STV servo, so, you can nudge it to get the correct resistance, (just push on the STV a touch, and the reading will come into range. What we did was to find the happy medium between the open and closed values, without manually touching the STV themselves. I found that we couldn't get the full range of adjustment that we needed, it would bias too much closed, or not enough open, or vice versa. So by moving the pot back and forth, and considering the slop in the servo drive, it comes to being damn close to spec.

Q  Originally Posted by motormouse
Are you settling on a happy medium, or moving more to the high or low side of the range?

A  We biased it pretty close to the middle.

Q  Originally Posted by John.
How does this differ from the Suzuki method of setting the STV position sensor voltage at full open?

A  There is a trouble shooting test that you use with key on, and metering the voltage.
The ECU is looking for the resistance of the STV sensor, so it can compare with it's map, to put the STV's in their proper place.

Q  Originally Posted by andmoon
I've mentioned this before...and you all get to read it again...The dl boys are removing them altogether and reporting crisper response w/ out any of the abruptness (that the secondaries are supposed to calm) or the drowning (as in flatslides)....I have removed mine and noticed no diff. I wonder if removing them equals running w/ them properly set.

A  Could be....Usually if the manufacturer puts time money and research into something, it's usually installed for a reason. Way back when the emissions thing just started with autos, it was somewhat of a challenge to get around these power robbing devices, just to get them to run better. Problem was that technology wasn't in place as it is today (cool computers, and software), to manage such changes. Most of it was a bolt on thing, make the engine run as lean as it could without dumping Hydro carbons out the tail pipe. (if you go too lean, the HC's will show rich!) anyway, they are there, the have adjustments, we know the principle behind them.....so......

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