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Discussion Starter · #1 · (Edited)
AKA: No User Serviceable Parts Inside.

Since I've owned my bike its always had a minor problem with an unsteady idle (hunts below 3K RPM) and coming off idle but otherwise runs great. I tried to sync the throttle bodies but the front idle screw was stuck (its probably never been touched in 85K miles) so I did what I could with just the rear screw but it didn't really help. I finally had a chance to pull my throttle bodies to get that screw unstuck and I took the opportunity to test the sensors per the service manual (all passed) and to examine the TB up close. Previously I had noticed, after a long hiatus, that the secondary valves were stiff and hard to move which I freed up with a shot of WD40 but it seems to have returned after only 5000 miles. I never got an STVA C28 code but I didn't like how they felt and thought maybe it was connected to the idle issues. So with the throttle bodies on the workbench I proceeded to take apart the front secondary butterflies for an inspection and stumbled onto the cause of both problems and down a rabbit hole.



As you can see in the photo my shaft seals are shot. That is the seal for the front secondary valve shaft and its not suppose to be cracked like that and was probably leaking and causing the stiff operation and unsteady idle. I immediately went to some parts sites and learned that the throttle bodies are not serviceable and there are no rebuild kits available. I found a used K9 throttle body on ebay for less than $100 and ordered it figuring I'd just do a swap. However, when the part arrived I discovered that it was a non-E33 (California) throttle body and does not have the vacuum ports for the charcoal canister. I was reluctant to install the non-E33 TB and I thought about using the K9 for donor parts but I was afraid that I'd just end up with two non-working throttle bodies. The service manual and the word on the street is that if you mess with your throttle bodies they'll never work right because only Suzuki can properly sync them (more on that later). After dismantling the rest of the throttle body shafts here is what I found.




There are six 11.5x6.0mm shaft seals, one 9.5x6.0mm seal (FIXED:I made a mistake on the label in the picture, it should be 6.0mm ID not 6.5mm) for the rear secondary that mates to the STVA via that brass fitting. The rear primary shaft that terminates into the TPS is sealed by the sensor o-ring so that one was not a problem. By doing searches for Mikuni Carb Rebuild I was able to track down the 11.5x6.0mm seals (Yamaha part number 256-14997-00) but came up empty for the 9.5mm seal . Fortunately, that shaft is also sealed by the secondary TPS o-ring and my seal was in decent shape so I just reused it. One problem that I discovered is that the secondary shaft seals are a bit different than the primary shaft seals. Here is a picture of a Yamaha seal.



The seals go into an 11.5mm dia. well in the TB with that groove facing out and are flat on the other side. The primary shaft seals are grooved on both sides. I was a little concerned about this difference but I read on some forums that the double grooved seals on the primary shafts are used to give less drag for hand-operated throttles. I didn't really care about that and since I didn't have much choice I figured I'd go with what I got and used the Yamaha seals for all the 11.5mm wells. One other thing I found is that the shafts on my throttle bodies are all scored.



I think what happens is the seals start to leak and the grease get sucked out and the shaft runs dry. When I was cleaning my throttle bodies I found old, dry powdery grease in the journals that had no lubrication properties whatsoever. I really think that TBs need to be serviced around 50-60K miles but Suzuki makes that difficult to say the least. I probably should just replace my throttle bodies with its scored shafts (it looks worse in the picture than it really is) but I wanted to try and solve the puzzle of how to get throttle bodies resync'd. I have some ideas on how to resync butterfly valves (those adjustment screws on the linkage) and the idle speed screws with a new method to lockout the ISC during sync. If I fail I have the K9 bodies as backup.

I'd love to share all the steps of rebuilding the throttle bodies but there are so many details as to be impractical. I have rebuilt carburators and its very similar to that process but without jets or bowls to mess with. You can watch youtube vids or read other forums on how to do it. In difficulty scale I'd rate it about a 7 or 8 on a scale of 10, so its not really for beginners. I can share a couple of potentially fatal pitfalls I ran into and maybe that will save someone some grief if they choose to go down this path.

Pitfall#1: The secondary butterflies discs come right off and the screws are retained only with loctite but be sure to use a JIS bit not regular Philips bit to avoid marring the screw heads. The primary butterfly screws are peened on the back side with a waffle pattern after they are attached to prevent them from backing out and getting sucked into the engine (or maybe to prevent people like me from servicing non-serviceable components).



That waffle pattern needs to be filed off BEFORE extracting the screw and removing the primary valve discs. I skipped this step and almost ruined my shafts because the peening mauls the thread on the way out. I was able to recover the threads using another longer 3mm screw to chase the threads. You'll need new valve disc screws for the primaries but they are the same size as computer hard drive mounting screws (fine threads) and any repair shop should have a whole pile of them. I used flathead screws instead of rounded heads on both primary and secondary valve discs.



The "before" picture is on the left and the "after" picture is on the right. You can see how much the OEM screws block the flow of air through the TB throat. I did the areal calculation and the flat screws are roughly a 1% increase in the effective throat diameter so this is a performance upgrade to 40.4mm dia. throttle bodies! I used blue loctite on all the screws but I didn't have a peening tool so I put a dab of nail polish on the screw heads and tails to prevent them from backing out and getting sucked into the motor.

Pitfall#2: On reassembly, do not tighten the primary shaft bolts until the butterfly valve discs are installed. In the shaft picture above you can see that the shaft has a gap to hold the valve disc and it is easy to torque the shaft so the valve won't slide in. I got a valve disc wedged in the shaft and TB throat trying to reassemble it but fortunately I was able to extract it and avoid this fatal error. To untweak the shaft I put the threaded end in a vise and turned the lever CCW until the valve disc would cleanly slide in and out of the gap. I used Lucas Assembly Lube which is a moly based grease and very sticky so I think it will resist being sucked out of the shaft journals and running dry. Also, there are grooves in the TB journals that I think are little pockets to hold extra grease so I made sure those were filled with lube using a q-tip. All seals new and old were treated with Trident Pure Silicone Grease to keep them from drying out and hardening. Divers use this grease to rebuild their regulators on which their lives depend so its good stuff and keeps rubber seals supple and working for a long time.

Pitfall#3: Be sure to take a lot of pictures before disassembling your TB. I had the K9 TBs to look to when I had reassembly questions and it was invaluable to getting everything back together in the right order and orientation but pictures will work too.

Pitfall#4: This brings me to the final pitfall and the one I have jumped into on purpose. Riders who have touched the linkage adjustment screws have never been able to get their throttle bodies working correctly. I was able to disassemble and reassemble my TBs without touching the linkage screws but I think that is a false hope, I can visually see that the disc are now out of whack. Suzuki/Mikuni probably have a complex and terrifically expensive flow and measurement machine to get it right. Base on my own research the linkage screws have to be adjusted to around 0.01-0.02mm accuracy which is a tall order for a DIY mechanic. The valve discs have four positions that have to be coordinated with those screws and the throttle stop adjustment; closed, stopped, cracked and F/R sync. The reason the accuracy is so tight is that throat flow rates are highly non-linear when moving from stopped to cracked open and a tiny error will cause problems when it transitions from the idle circuit to the main flow. I will post more details on this and the procedure to get the TBs sync'd but first I have to develop a new tool.

I noticed when rebuilding my TBs that if you hold the throat up to a bright light that even when closed there is still a tiny bit of light that shines through the primary valve discs. If you just touch the shaft lever to crack the valve disc open the light increases dramatically. So my plan is to use photons and not air molecules to get the valves resync'd. Here is a sketch of my tool that I am working on.



At the bottom of the TBs I will add a diffuser to spread the light out so the whiteness behind the valve disc is uniform with no "hot" spots. I think a piece of a white t-shirt and a rubber band will work. I already have a couple of small really bright white LED flash lights that will fit the fuel injector ports and illuminate the diffuser. At the top of the TB I will cap it with a small light detector which will feed into the measurement circuit and be used as a proxy for air flow. I think with a sensitive enough detector, adjustable gain and zeroing adjuster that I can get these TBs resync'd. However, I am ME not EE so desiging this circuit is a bit out of my wheelhouse. I am following this electronics tutorial in the link below to develop my circuit but if there are any electronic experts out there please feel free to advise.

Light Sensor including Photocell and LDR Sensor
 

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Discussion Starter · #2 · (Edited)
Addendum

Some missing pictures in post #1:

Yamaha seal:
Throat Screws:
Sync Tool:
 

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FORUM GODFATHER.....R.I.P. PAT
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Outstanding. Deserves a sticky. Now maybe all those people anxious to play with the linkage will desist.
 

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There are a number of "Bearing" supply stores around the country. These also have a large stock of seals. While you are thinking metric, you might find SAE seals that are for all but description and exact fit. Some of these places have a rather easy search menu where you can search sizes and even pull up drawings of dimensions of the seal.

How much play was in the throttle body housing to shaft? That is where most problems come from, this is a cast bearing surface on most models and hard to make it right.
 

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Discussion Starter · #5 ·
Outstanding. Deserves a sticky. Now maybe all those people anxious to play with the linkage will desist.
Thanks GW. This is really a high precision adjustment but I think it will work. Let's hold off on the sticky until I prove the procedure works. I don't want it to be the "sticky of shame" when I fail and have to throw in the K9 throttle bodies.
 
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The construction details and parts insights alone are enough to qualify for a sticky.
 

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Discussion Starter · #9 ·
There are a number of "Bearing" supply stores around the country. These also have a large stock of seals. While you are thinking metric, you might find SAE seals that are for all but description and exact fit. Some of these places have a rather easy search menu where you can search sizes and even pull up drawings of dimensions of the seal.
The odd ball 9.5mm OD seal is probably not super critical as it is backed up by the secondary TPS o-ring. The primary shaft on the TPS side only has the o-ring which implies this seal is somewhat redundant. I got most of my info from reading vintage motorcycle forums where they are always rebuilding their carbs (one main reason I got a bike with fuel injection). Some carb rebuilders us x-rings to replace the throttle shaft seals so that is an option. In my case, I just want to get it running and didn't want to spend a lot of time spec'ing and chasing parts. The Yamaha seals should be fine and are readily available. Hopefully in time others can track down a complete parts list and add it to the thread.

How much play was in the throttle body housing to shaft? That is where most problems come from, this is a cast bearing surface on most models and hard to make it right.
This is a great question and I didn't measure the slop but it could be a significant factor in getting it sync'd. The scoring didn't groove the shafts and there was no lip or edge to the marks. It looked like it had just taken the black finish off the shafts. I think if it went on much longer the shafts would be ruined too but I think I caught it in time. In any case, I'll just have to see how it will turn out. If I can get the valves/linkage sync'd I think it will at the very least run/idle better with new shaft seals.
 

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Discussion Starter · #10 · (Edited)
I highly admire your skills and patience, I would've just bought a new bike with some of the issues you have been having.
Thanks but my patience is really about waiting for my next and (probably) last bike, the 2014 DL650A (in red, of course), to age into the used market. My K7 is my "practice" bike to work on till I can replace it. I like wrenching on my bike and my "issues" have actually been fun projects for me to tackle. This project evolved from my original goal to be able to sync the TBs without the SDS tool or paying Suzuki to do it so its all been a fun learning experience.
 
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Discussion Starter · #12 · (Edited)
Light at the End of the Throttle Body

Note: I moved this post to its own thread in the maintenance forum because this thread is focused on rebuilding the throttle bodies and resync'ing is a separate procedure that can be done regardless of whether you rebuilt the TBs.

Throttle Body Butterfly Sync
 

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I can see that procedure for synching the butterflies. Those trying it need to remember the K7 and later 650 throttle bodies also have air screws that allow air passage in addition to the air passing the butterfly openings. They will need attention too.
 

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Discussion Starter · #14 ·
I can see that procedure for synching the butterflies. Those trying it need to remember the K7 and later 650 throttle bodies also have air screws that allow air passage in addition to the air passing the butterfly openings. They will need attention too.
Yes, that is an important point I tried to make in the last paragraph of my update post, perhaps I wasn't clear. As mentioned, I have a new procedure to sync those air flow needles with ISC lockout that I am excited to try out.
 

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I just mentioned it because it is a long post and I wanted to be cautious.
 

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Discussion Starter · #16 ·
Vroom, Vroom!

Runs great!

Quick update: I got it running today with the rebuilt throttle bodies and its like night and day. Idles much better, pulls out of the hole better, pulls strongly to redline, seems to even shift better! One really noticeable difference is that the engine is much smoother at speed. Since this is my first V-Strom I didn't know how much vibration there should be cruising down the highway but now with rebuilt TBs its much less "viby" at freeway speeds. It is really amazing how smooth it runs now. I haven't even finished the work as all I've done is the dealer mode idle reset procedure and still need to set the throttle position sensor and the idle air needle sync. I can't wait to complete it and take it for a spin in the twisties.
 
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Discussion Starter · #17 · (Edited)
The Good, The Bad and the Ugly

The Good:

As mentioned in my previous post, the bike runs great with the rebuilt K7 throttle bodies. The rebuild and resync has totally changed the dynamics of the bike and now it runs silky smooth all the way to redline. The motor pulls into the rev limiter without a hint or complaint (something I try to avoid) whereas before it was wheezing at the limit. The motor feels smoother and freer breathing, more responsive at all RPMs and the vibrations are gone except at a few resonant frequencies which is normal for a 90deg V-Twin and easy to avoid. Low speed motoring, like pulling into the garage or jockeying for a pump at the gas station, is much easier. I can use my mirrors as they are not so blurry at speed. Instead of feeling the motor vibration in the foot pegs I can actually feel the traction of the road. This has increased my confidence in the turns so much I can now comfortably drag a peg feeler in the twisties. The "sweet spot" of the motor has shifted from about 5.5-6K RPM to 6.5-7K RPM which is a big factor in the change in the dynamics of the bike. I don't know if it has more power or torque but I inadvertently chirped the rear wheel coming out of a turn and passing a Prius which it never did before. I am literally relearning how to ride this bike.

The Bad:

Previously, I installed the 16T front sprocket because the bike was so buzzy at freeway speeds but now I'm probably going to go back to 15T to keep the revs up and in the peak power zone. Unfortunately, with the higher revs I am burning more oil and catching more oil in my catch can. The rear cylinder fouls spark plugs in 5K miles so I was planning on replacing the valve seals soon with the rope-in-the-cylinder trick.

It turns out that those special double-grooved primary shaft seals are not optional. They INCREASE drag on the throttle and without them the throttle is too touchy. I was getting way too much road-bump throttle input without them. Tragically, the K7 TBs still would not hold a steady idle around 3K-4K RPM and after ruling out any vacuum leaks I had to conclude that it was the worn, leaky shafts so all my work was for naught.

The Ugly:

Because of the overly touchy throttle and ongoing low RPM hunting, I installed the K9 throttle bodies as I received them from an ebay sale (not rebuilt or resync'd) as a test. It ran and idled fine (no hunting) with the newer throttle bodies but the bike was not nearly as responsive and the motor vibrations returned. I really missed the smoother motor and the performance of the rebuilt TBs. I thought about using the K9 shafts in my K7 throttle bodies but I was concerned that the journals might be worn too, not just the shafts. So I rebuilt the K9 throttle bodies with three new Yamaha seals and refurbished all the primary seals and the special 9mm secondary seal. I cleaned the seals with rubbing alcohol then soaked them in Listerine (a trick from the vintage bike forums) then coated them with Trident Pure Silicone Grease. So the ugly part is I did two TB rebuilds and three TB swaps in a couple of weeks.

The End:

I am happy to report that the rebuilt K9 throttle bodies are installed and run great. No idle hunting, no road-bump throttle input, no motor vibration and an amazingly responsive motor all the way to red line. I think the sync method that I devised for this project really makes a huge difference in the balance of the motor. I suspect that the flat head screws that I used on primary and secondary plates noticeably improve the performance of the motor but I don't know that for sure. All I know is that if I bought a new bike the first day off-warranty I would do this rebuild. I recommend this rebuild for anyone who has a high mileage bike (~50K miles or more) before your shafts are ruined but also it will breathe new life into your motorcycle. The improvement is dramatic.
 
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