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Discussion Starter #1 (Edited)
So much misinformation about the STVA flying around these days about the STVA function, and failure repair that I thought I'd step in and shine some light. In case you're wondering, yes, I am TheGeek.

First, let's start with why the STVA is there in the first place. The intake runners on these bikes are pretty small. That means not much volume. This makes them very sensitive to changes in the vacuum. Without getting too technical, a rapid decrease in vacuum is going to throw off the fuel mix for a very short time and cause dips in the power curve. Not a good thing when you're getting back on the throttle mid corner. Remember that small volume I spoke of? The air mass in there moving toward the intake valve is important. Google mototune and the 8 cycle engine to learn a little more about precompression intake. By controlling the vacuum, you can also control this air speed.

The whole point is pretty simple. Maximum smooth possible power. I don't care what your butt dyno says, removing the secondary plates doesn't help your torque or peak HP. The intake runners are tappered and the lower valve is more restrictive than the upper valve fully open. In fact, having the STVA working improves low to midrange torque by allowing the bike to measure and maintain optimal vacuum.

The STVA between the k4-5 and the k6-7 generations are essentially the same. Both are manufactured by Mikuni and both use a Mineba-Matsushita bi-polar stepper motor to drive the system. There are a few small differences.

The K4-K5 was the first to use this particular motor. As such, there were bound to be problems. What it all boils down to is that this motor was never intended to have a hard connection to a plug. Combine that will cheap production, and a high vibration application and something is going to break. The k6-k7 is slightly different. They changed how it's mounted to free up some space, but the motor was also changed. Mukuni and M-M both changed a couple things to help solve the problem. It's much stronger, but it still suffers from poor implementation. The small, but very important difference is the STPS. On all of these, the STPS is spring loaded. On the k4-5, it's spring loaded to the fully closed position. On the k6-7, it's spring loaded to the fully open position.

Removal of the STVA is easy, but installation requires knowledge of how to get everything setup. If you do happen to have an STVA to install, use a small screwdriver to turn the action to the correct position so that the sensor is lined up. On the k4-5, you'll turn the action fully clockwise, and on the k6-7 fully counter clockwise. When you do this, don't insert the screwdriver more than 3/8". If you engage the STPS while turning the action, you can easily damage it.

So what do you do with the failure. Honestly, hire someone to fix it. All of the units I've seen that couldn't be fixed are because someone without the proper skills made some serious mistakes. A few years ago, this wasn't that big of a problem. Now, parts are getting difficult to find.

Before you go searching ebay for STVA fixes/replacements, do some testing. From an electrical point of view, the STVA is pretty simple. I’ve attached two zip files with testing instructions for both generations. Regardless of which generation you have, I suggest you read both when you go to do your tests. The pictures in both documents will help increase your understanding of the tests. The procedure and results should be the same regardless of generation of your bike, but things just look a little different. The main reason to test is because the more recent C28 codes on the k6-7 bikes have been caused by the ECU. My theory is that with the known regulator/rectifier issues, there's some spikes or dips that are damaging the stepper control on the ECU. And, if you're lucky, your fix will be a little effort and $0.20 worth of electrical tape to correct a broken wire. :thumbup:
View attachment K6-K7_STVA_testing.zip

View attachment k4-k5_STVA_wiring_tests.zip
 

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Nice write up!

My friend recently got the dreaded c28... fortunately for us the wires going to it were severed...
So we didn't have to remove/crack the thing open, just splice together the wires for it and voila.
Good to know why it's important, though!
 

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The Bestest Racer
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I successfully replaced parts of my 2001 750 SVTA with a later model exhaust actuator's internals. Its as simple as swapping over the board, the front half, and the external cam.

The 00-03 SVTA is different from the 04+ design in that it is remotely mounted and uses two very short cables to move the butterflies.

Thanks for the write up ... I've always wondered why people would remove their secondaries. They are there for a very good reason, and your engine is designed to run with them. Snapping open the throttle at low or mid RPMs without the secondaries makes the engine fall flat on its face.
 

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Last summer i had this happen on my 05 600.I fixed it my self, wasn't to bad.
 

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Discussion Starter #5
Difficulty is relative. I work on multi-million dollar equipment every day. To me, this is really simple. Some people can't even solder correctly.

Where things get confusing is when you look across the GSX-R family from 2000-2004. There were 4 different variations of the STVA. There's the current stepper motor design, which is now made by Keihin in the newer bikes. There was the old remote cable driven unit (and the parts fiche calls it an exhaust servo for some reason) that is driven by a DC motor. That DC motor just wears out. It's got brush contacts that can be replaced if you know how. It's not real easy to get right. Then there's the one that mounts directly to the shaft on the 600. It's just plain stupid. Probably explains why it was only used two years. And then there was the first generation of the newer stepper designs that used a remote stepper control.

If you want to compare the SDTV system to something a little older, you just have to look at a CV carb. The CV carb uses vacuum circuits to control the slide and maintain air velocity. So the concept has been around a lot longer than the EFI systems, and just needed to be implemented in a different way with the addition of EFI.
 

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Chuckster amazing post! Lots of well communicated information!

I previously had this problem with my K4. Tested the STVA, pulled it apart, resoldered all the connections, tested it, reasembled it and it was good as new.

Now my K6 is having an issue. My regulator fried and after replacing it, my bike has been throwing a C28 code. My plan tonight was to remove and test my STVA and repair if needed. After reading your post I'm worried that my ECU may have been damaged with the regulator failure.

So if I go home and the STVA tests bad, I repair it and the code disappears; everything is right with the world. But if I go home and the STVA test good or I repair it and the code remains and/or the bike continues to run in safety mode.....what are my options?? Am I looking at a new ECU??

Also the zip files above aren't working. I get a invalid or corrupt message. Can you repost them? Would you/anyone email them to me??

Thanks
 

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Discussion Starter #7
Probably something to do with your computer. They open fine for me on 2 different machines. PM me your email address and I'll send the uncompressed files.

If it tests bad, you could get lucky and it be the wiring. But, if you had R/R problems, I wouldn't be too hopeful. Test it before you remove it. On the 06/07, it's a whole lot easier to test since everything is facing up.
 

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My Computer cannot open this file, is there any other way i can get to see the k6-k7 testing without the ZIP file?

i need to repair my C-28 error this weekend and have a few printed pages on how to do so. this one seems by far the best so please someone HELP this poor fellow... me:D

:headshake Damn C28....

Chuck please email me the same [email protected]

i have a k7 and the R/R went bad because my xenon lights didnt come on resulting in the frying of my R/R.

i replaced it and went back to stock headlights. im hoping its also just wiring. otherwise i do have soldering experience and will need to take the stva out.
 

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Discussion Starter #9
I'll email them when I get home. Basically, it's a couple word documents that I put together. They contain some photos I took on my bike for the 04/05 that will help you understand the concepts on the 06/07. All this information is in the service manual. I just clarified/simplifed/consolodated it.
 

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Chuckster, I threw my email on ur vistitors wall on ur profile since it won't let me send you a PM. Thanks a bunch!
 

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Hey Charles!! :thumbup:

EDIT: I had Chuckster fixed my STVA when it broke.. Great guy!
 

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A mighty fine reputation follows TheGeek..nice information :thumbup:

Edit: This thread should be a Sticky or in the Technical FAQ's section..Wake up Mod's...:shifty
 

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Thanks Chuckster! :thumbup:

i received the doc's :bowdown:

absolute legend
 

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Threads dont get as much notice once they are moved to the Tech FAQ section since not every one clicks on "new posts".

Once this starts to not get so much attention I will move it there because it def deserves a sticky to keep it alive!

Good write up.
 

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Just picked up a 2009 gsxr 1000. Starts and runs fine, but FI light kicks on when you put it in first. Comes out with a C28 code. STVA same on the 09 model 1000?
This is going to be a track bike, so I'm not super concerned about it if it will be a PITA.
 

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Discussion Starter #18
Nope. That bike uses a Keihin throttle body. They don't suffer the same problems as the 04-07 Mikuni units used on the 600/750.

Honestly, the Kehin units are bullet proof. Your problem is either with the wiring or the ECU. If you test the STVA from the ECU connector on the harness, you'll be able to tell where the problem is. I'm not sure why, but the ECUs on the 06 and up bikes seem to be pretty weak.

So, if this is going to be a trackbike, I'm guessing you'll be riding the dog shit out of it. That being the case, you won't want the bike in limp mode. As long as the FI error exists, your bike won't perform to it's full potential.
 

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Checkster...

I gave this thread a sticky as requested by some members. Im leaving it right where it is for now tho. Not in the FAQ, its very well written and very helpful and I want ppl to see it since this seams to be a common problem right now.

After the views/hits die a little Ill move it where it can live a long happy helpful life in the FAQ.

Thanks broham
 

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Damn STVA problem on Suzuki GSXR 600 K4

Help mi out guys, 2 weeks ago I changed oil, oil filter, cleaned my K&N filter and regressed it with K&N cleaning kit, after a few rides I got a C28 error. After I opened my bike, removed the air filter I saw when I turn the ignition on the STVA butterflys are not moving and I noticed they are a bit sticky. Is it possible that I put to much grease on my K&N filter so the oil leaked on the butterflys. After I tried to clean them and put a little bit of WD40 on the edges of the moving rod and moved them a few times with my hand and turned on the ignition, there was no error C00. But after a few miles FI light gets turned on again.

Please help me, should I clean the hole STVA, should I put wd40 or something to help them move easier, becouse they are a little bit stiff.

I didnt measured electrical circuits yet.

When te FI indicator comes up and I turn the ignition on I can hear rattling sound and the butterflys are not moving (they are trying but nothing si happening.

Please help.
 
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