Good morning all.
I had a topic open on vacuum hoses, but my issue appears to be totally different, so opened another topic.
The secondary valves on the throttle body are not moving when the ignition is switched on.
I have the airfilter out and can move the valves manually and this clearly the shaft that operates the STPS.
Has anyone had this and fixed it? I can't see a replacement motor online anywhere.
I am thinking of getting a full used throttle body.
Have a search on here, you should be able to pull the stva apart to see whats wrong, alternatively check the TB once you've removed them from the bike. If you have access to another set of tb's, verify of course that the stva works, you will need a 5V supply, I think 12v will be too much.
Pretty sure it was Snapey repaired his, re glue magnets from vague memory. Worth searching before rushing in IMO
This isn't the best pic as I can't find the ones I took of the STVA in bits, but the big square lump made of thin layers in the centre of the TBs is the STVA. You get to it by taking the TBs apart, there's two long bolts that hold them together end to end with, I think, 10mm heads on the RH side of the bike. Then there's four little nuts from the LH side that hold the plastic cover on the side of the STVA. Once you lift that off you'll see the magnets in there, if they are loose then glue them back (epoxy works) where the marks are from them being glued previously.
14 STVA Rear (600 x 450).jpg
Exactly, as Dr. Hooli says.
Thanks all, brilliant help as always.
Having a weekend off, so will look again next week.
Ian
Well, throttle bodies out and long bolts removed.
Unfortunately I don't have JIS screwdriver head to take the fuel rail off to allow me to separate the bodies. On order for tomorrow.
However, I have found an issue.
There is a spring missing. Can't describe it, but the picture shows it. This missing is stopping the right hand secondaries moving the same as the left two. So definitely needs anew one. Don't suppose anyone would know where I could source such a beast?
0
Ahh those springs, they often pop out as you're twisting the TBs put when the long bolts are out.
You can probably get real ones from Webike Japan, but I've often found random springs that look about right and used them. One thing I'd say, is don't use ones that are too soft as the throttle vacuum can overcome the spring and give alsorts of odd issues.
I can't suggest where to find them locally though as I nicked the last ones I needed from some 125cc carbs in the corner of the garage.
If you can get a complete set of TB relatively easily, you could cannibalise one to make a complete full set.
Do not leave out AliExpress. An example:
https://es.aliexpress.com/item/1005008369380644.html?pvid=37e5f6ba-83bd-48ac-9db1-ed6453d6fe99&_t=gps-id%3ApcDetailBottomMoreOtherSeller%2Cscm-url%3A1007.14452.396806.0%2Cpvid%3A37e5f6ba-83bd-48ac-9db1-ed6453d6fe99%2Ctpp_buckets%3A668%232846%238108%231977&pdp_ext_f=%7B%22order%22%3A%22726%22%2C%22spu_best_type%22%3A%22price%22%2C%22eval%22%3A%221%22%2C%22sceneId%22%3A%2230050%22%2C%22fromPage%22%3A%22recommend%22%7D&pdp_npi=6%40dis!EUR!2.43!2.42!!!18.92!18.81!%40210388c917779591547783402ee22d!12000044772289354!rec!ES!135463698!X!1!0!n_tag%3A-29919%3Bd%3A26674c2d%3Bm03_new_user%3A-29895&utparam-url=scene%3ApcDetailBottomMoreOtherSeller%7Cquery_from%3A%7Cx_object_id%3A1005008369380644%7C_p_origin_prod%3A&search_p4p_id=202605042232348122981266911596170176_1
So those springs just sit there, nothing holding top end in just spring tension?What adjustments is the screw for? Never messed with TB on mine, never needed to. Just wondering.
Quote from: grog on Tuesday, 05 May 2026, 04:33 PMSo those springs just sit there, nothing holding top end in just spring tension?What adjustments is the screw for? Never messed with TB on mine, never needed to. Just wondering.
no, there is a screw in the bottom bit, same as the top, but looks like that screw is also missing, that holds it in place. The spring force should hold the screw in. Suspect they may have some loctite on them to ensure. I have adjusted mine, as I found that the voltage reading on the STPS when opening #1-#2 by hand was different when doing the same with #3 and #4, which meant that 1-2 and 3-4 were not opening together. Fine adjustment is possible to ensure that they do, and allows accurate TPS and STPS setting.
Thanks Eric 👍Looks like correct parts needed then. Parts diagram says discontinued, that's if I'm seeing correct bits, lots of little bits in TB diagram.Hard on old eyes to see
Quote from: grog on Tuesday, 05 May 2026, 04:33 PMSo those springs just sit there, nothing holding top end in just spring tension?What adjustments is the screw for? Never messed with TB on mine, never needed to. Just wondering.
As Eric said, you can balance the secondary throttles just like the primaries.
When I've had TBs off I see if they look equal & if not adjust them slightly. I tend to push them nearly shut at the STVA & use a drill bit to slide in past them to check all the gaps are the same without moving anything.
Another update!
All in bits and no loose magnets.
Bugger!!
Next plan is to throw the bike in the skip.... :lol:
Well at least that eliminates one suspect. Im pretty sure the STVA motor only drives the shaft at #3-#4 throttle bodies, and relies on the linkage to #1-#2 for them all to work, so with your missing spring and screw, it may have tried to, but as the secondaries open reverse to the primaries, nothing happens.
But you did mention you saw none of the secondaries move. Also pretty sure the stva motor gets 5v from the loom, so best to check that too.
Quote from: Eric GSX1400K3 on Wednesday, 06 May 2026, 10:39 AMWell at least that eliminates one suspect. Im pretty sure the STVA motor only drives the shaft at #3-#4 throttle bodies, and relies on the linkage to #1-#2 for them all to work, so with your missing spring and screw, it may have tried to, but as the secondaries open reverse to the primaries, nothing happens.
But you did mention you saw none of the secondaries move. Also pretty sure the stva motor gets 5v from the loom, so best to check that too.
No, secondaries never moved. Got a genuine spring coming, so once in place I will temp fit bogy and tank back on the bike to see what does and doesn't move.
In the mean time will give everything a check and clean.
Quote from: Barbastro K6 on Tuesday, 05 May 2026, 03:35 PMDo not leave out AliExpress. An example:
https://es.aliexpress.com/item/1005008369380644.html?pvid=37e5f6ba-83bd-48ac-9db1-ed6453d6fe99&_t=gps-id%3ApcDetailBottomMoreOtherSeller%2Cscm-url%3A1007.14452.396806.0%2Cpvid%3A37e5f6ba-83bd-48ac-9db1-ed6453d6fe99%2Ctpp_buckets%3A668%232846%238108%231977&pdp_ext_f=%7B%22order%22%3A%22726%22%2C%22spu_best_type%22%3A%22price%22%2C%22eval%22%3A%221%22%2C%22sceneId%22%3A%2230050%22%2C%22fromPage%22%3A%22recommend%22%7D&pdp_npi=6%40dis!EUR!2.43!2.42!!!18.92!18.81!%40210388c917779591547783402ee22d!12000044772289354!rec!ES!135463698!X!1!0!n_tag%3A-29919%3Bd%3A26674c2d%3Bm03_new_user%3A-29895&utparam-url=scene%3ApcDetailBottomMoreOtherSeller%7Cquery_from%3A%7Cx_object_id%3A1005008369380644%7C_p_origin_prod%3A&search_p4p_id=202605042232348122981266911596170176_1
Excellent post mate! Would you recommend the spring that is listed when clicking the as the OEM counter part or some different size?
would need a sample to place order or else diameter of the base where it rests and the length.
It is probably a size that is widely shared by other models
and more examples
https://es.aliexpress.com/item/1005008770091952.html?pvid=32a69059-7fc9-4aba-822a-0be153596b2b&_t=gps-id%3ApcDetailBottomMoreOtherSeller%2Cscm-url%3A1007.14452.396806.0%2Cpvid%3A32a69059-7fc9-4aba-822a-0be153596b2b%2Ctpp_buckets%3A668%232846%238108%231977&pdp_ext_f=%7B%22order%22%3A%22305%22%2C%22eval%22%3A%221%22%2C%22sceneId%22%3A%2230050%22%2C%22fromPage%22%3A%22recommend%22%7D&pdp_npi=6%40dis!EUR!2.23!2.22!!!17.38!17.29!%40210384b217780952408354285eee27!12000046598189395!rec!ES!135463698!XZ!1!0!n_tag%3A-29919%3Bd%3A62c4862b%3Bm03_new_user%3A-29895&utparam-url=scene%3ApcDetailBottomMoreOtherSeller%7Cquery_from%3A%7Cx_object_id%3A1005008770091952%7C_p_origin_prod%3A&search_p4p_id=202605061220408702349902977116214877_1
I have got two new springs!
Due to my old fingers, I have pinged them both accross the garage!
I surrender!
More ordered, but away at sea for a month tomorrow, so my nc500 trip for when I get back is on hold.
Quote from: Idh on Monday, 11 May 2026, 07:30 AMI have got two new springs!
Due to my old fingers, I have pinged them both accross the garage!
I surrender!
:coffeescreen:
Been there, done that.
D.D.
Quote from: Idh on Monday, 11 May 2026, 07:30 AMI have got two new springs!
Due to my old fingers, I have pinged them both accross the garage!
I surrender!
More ordered, but away at sea for a month tomorrow, so my nc500 trip for when I get back is on hold.
Silly boy!
It's so easy to do though.
Quote from: Idh on Monday, 11 May 2026, 07:30 AMI have got two new springs!
Due to my old fingers, I have pinged them both accross the garage!
I surrender!
More ordered, but away at sea for a month tomorrow, so my nc500 trip for when I get back is on hold.
Happened to me as well mate. The scary thing is that a couple of days later, I found a random spring in the garage which wasn't even the one I had lost...
Quote from: Idh on Wednesday, 06 May 2026, 04:57 AMAnother update!
All in bits and no loose magnets.
Bugger!!
Next plan is to throw the bike in the skip.... :lol:
Those magnets should be opposite to each other so one of them is loose.
Quote from: Snapey on Thursday, 28 May 2026, 08:09 PMQuote from: Idh on Wednesday, 06 May 2026, 04:57 AMAnother update!
All in bits and no loose magnets.
Bugger!!
Next plan is to throw the bike in the skip.... :lol:
Those magnets should be opposite to each other so one of them is loose.
Oh, Thank you, good spot!
I am still away ar sea for 2 weeks but will have another look.
To complete this post, I ended up buying a used throttle body.
Just installed it.
I removed the Pairs system while I was on.
Still not running brilliantly, but a lot better than before I started!
Will completely strip, clean and rebuild the original body and swap it out once done.
Thanks for everyone's input and help.
Ian
Good luck mate!
Quote from: Snapey on Thursday, 28 May 2026, 08:09 PMQuote from: Idh on Wednesday, 06 May 2026, 04:57 AMAnother update!
All in bits and no loose magnets.
Bugger!!
Next plan is to throw the bike in the skip.... :lol:
Those magnets should be opposite to each other so one of them is loose.
I have pulled it all apart again.
I found a photo on line which shows them as mine are.
They physically cant go opposite each other.
So I think I am looking in the wrong place for my problem.
I have surrendered, going into a suzuki garage to get sorted or part exed!
Hmmm, have you checked the TPS and STPS on both the original and rebuilt throttle bodies? each should be getting 5V input, and if you connect a multimeter across the sensor pins, and reading Ohms, you should get a steady change in Ohms as you move the little rotating bit through its motion. Best done with the sensor off the bike and on the bench.
Watch the Ohms carefully, what can happen is that the tracks in the sensor corrode, so the signal drops away, leaving the ECU without an input, causing erratic running.
Usually a C28 code pops up, which when you read the book, is unrelated to the STPS. I had the same as you, ended up replacing both the TPS and STPS with genuine, she runs well now. Oh, and don't trust cheap aftermarket injectors, they fit, but don't flow enough fuel. Make sure the fuel rail is clean, plus the in tank filter and pump assembly. Injectors are pretty robust, mine are 24yo originals, still working fine.
Thanks Eric.
I have checked the ohms on each TPS and STPS on both.
I had to adjust to get the required setting. So they are good.
Not checked voltage. Will look into that.
Am tempted to replace them, but as both bodies have issues, not sure it's worth the expence just yet.
I suspect my original bodies have a power supply issue to the STPS motor.
Injectors are all original as far as I know.
If you test the SPS & TPS as the manual says, there's an extra check to do.
The manual says -
Test between the power & signal leads for a smooth change of Ohms over the full sweep.
Every one I've had fail passes that test but doing the following finds a fault -
Test Ohms between the power & earth leads over a full sweep - it shouldn't change, but all the failed ones I've had do change. I think they short to the resistive track the signal wire uses.
Someone on here found the info on a GSXR forum as they use almost the same sensors.
Thanks for all the assistance.
I have found that the STPS motor isn't working. It's getting 5 v supply, but not moving. Can't see where I can source a new one, but will keep looking.
So I am sticking with my spare second hand set. Was running very rough but after a second balance and TPS/STPS adjustment,it's running a lot better.
My balancer is a cheapy one, so going to fork out and go through the process again.
If no better, then this is now well beyond me, so will have to decide what to do.
Again, thanks for all the input.
Ian
Check the large grey connector on the lhs under the cover, thats what feeds power to the various sensors up at the TB. Could be a corroded connector or pin. From the photos you STVA looks clean and undamaged, they're well protected up under the throttle bodies. Maybe inspect the wiring coming into the stva. Also, double check the main connector at the ecu under the seat, lots of small pins there, easy to get one bent so it doesn't seat home.
I'll be impressed if you've broken the STVA motor, as I've never heard of that before. Except for the magnet issue mentioned earlier.
I know you said it's got 5v but is the earth ok? I believe the basic 5v signal voltage is just for the ECU to confirm it's plugged in, without a circuit at 5v you'd get the C28 error and as I recall you don't get any codes?
Sorry guys I take my hat off to you guys who delve this far in to bike faults. I've got zero clues about these things. :cheers: :devil:
Quote from: GSXKING on Friday, 10 July 2026, 07:59 PMSorry guys I take my hat off to you guys who delve this far in to bike faults. I've got zero clues about these things. :cheers: :devil:
I second that GSXKing. :onya:
Quote from: Idh on Thursday, 09 July 2026, 05:09 AMThanks for all the assistance.
I have found that the STPS motor isn't working. It's getting 5 v supply, but not moving. Can't see where I can source a new one, but will keep looking.
So I am sticking with my spare second hand set. Was running very rough but after a second balance and TPS/STPS adjustment,it's running a lot better.
My balancer is a cheapy one, so going to fork out and go through the process again.
If no better, then this is now well beyond me, so will have to decide what to do.
Again, thanks for all the input.
Ian
I had a throttle body in my hand a couple of days ago and to me it is a solenoid so it gets its voltage from the ECM depending on temperatures from other inputs, you should get a reading across the coil. You could put an external voltage 6 volt should be ok to see it it actuates if not it may be jammed or even the throttle body shaft.
OK. So, after all this time, there is a fault in the loom of my original throttle body. So, I have tested it on the loom of the spare body and the lead running into the STP motor has a has fault in it. So, tonight is swapping everything over and balancing and TPS/STPS adjustment. I might be liking her again by the weekend!
Nice find, I've not seen that before but the wiring on these is getting older after all.
Good find. I have noticed that some of the wires are tight, especially the wire leading from the lh grey connector to the stps sensor if its not routed correctly.
Throttle bodies in.
Balanced as best I can with a cheap guage
TPS set to 1102 ohms
STPS set to 803 ohms with valves closed.
I really didnt think I could make it any worse but apparently I can!
Missing a cylinder or 2 when running, even at high revs.
Think I am done. Not even running well enough to hide as a trade in!!
FFS what a :frustrated: moment!
Without seeing it, it's hard to suggest anything as you've gone through loads of stuff already.
Bugger. Im sure you would have checked 1-2 against 3-4, theres the two spindle screws that lock the butterfly shafts together, i use those to firstly ensure the butterflies open in sync, then double check i get the same tps readings when manually opening 1-2 and 3-4, same for the stps.
Im also sure you would have ensured that the plug leads are the right way around (its easy to mix up 2 and 3) and that they are seated properly on the plugs. Also, ive forgotten how many times ive had the tank back on,only to remember that id forgotten to reconnect the maf connector that sits directlu under the tank and the vac hose that runs to the joiner and other 4 smaller holes. Now i double check everything.
It was running before, so it will again, persevere, it will be worth it.
Agree, it was running before so something amiss in what you've just done.One more go👍
wouldn't have the plugs cross wired?
Quote from: KiwiCol on Saturday, 01 August 2026, 12:35 PMwouldn't have the plugs cross wired?
I will check but I have not had them off.
Just a thought as someone mentioned plugs. You've not knocked a coil connection off while doing the TBs have you?
And so the saga ends!
I am in love again!!
From last post, she was running on my 2 or 3 cylinders at best. So, my brain decided to swap back to the used throttle body I bought. From seat off, bodies swapped ready for balancing, 55 mins!
Still running like a bag of nails.
Brain clicked, checked sparkplug, they where coked up. Popped a new set in and hey presto!
As I took the pairs system out too, I think she's running better than she has in the 16 years I have had her.
So, in short, the issue started with FI error, after a lot of work and helpfrom here, the STPS motor wasn't working. Eventually found faults in the throtte body loom.
Looking at the wiring,the connectors are cracked and the main grey one actually fell apart,so age is catching up !
Thanks for all the help and support guys. Would never have done it without you
I am so happy!!!!
:boogie: :clapping:
Hurrah for the fix!
You should have at least two weeks to enjoy it now before they start salting the roads :lol:
Awesome mate, now ride the wheels off it.
:hat: off to you for persevering :boogie:
I'd never have undertaken anything you've done and documented here.
Future seekers of problem fixing will be knocking on your doors.
Well done :cheers:
Top job Mate 👏👍
Thanks all.
Now onto Tilly, my 1966 Triumph Speed Twin and an oil leak.
But that's another forum!
Tilly is gorgeous & they all do that sir!
Old Trumpy that doesn't leak😂 Nice lookin bike.Not much else I like about them.Yeah, I have owned, 750 Bonnie, slightly better than 850 Commando.Triumph leaked oil into primary case, 650 had a seal, 750 was a total engine builder, sealed bearing. Only had a 650 manual, cam timing marks were diff 750. Nightmare but got there.
I remember my late Dad hypothesising that the older British motorcycles were designed to leak oil due to crankcase pressure. Having only ridden some of them for short distances I can confirm I had oil on the shins of my boots from even that. Laverda was an exception, as they had a crankcase breather all those years ago. :boogie:
Laverda Italian
Quote from: GSXKING on Monday, 03 August 2026, 08:10 PMI remember my late Dad hypothesising that the older British motorcycles were designed to leak oil due to crankcase pressure. Having only ridden some of them for short distances I can confirm I had oil on the shins of my boots from even that. Laverda was an exception, as they had a crankcase breather all those years ago. :boogie:
All engines have crankcase pressure, but two big pistons moving together does move quite a lot of air around the crankcase. They do have breathers, older ones were timed to let out the excess pressure & create a partial vacuum as the pistons went up as less air in there results in slightly more power output. Later ones just had conventional breathers.
It's mostly poor quality parts and bad assembly that causes it. They are more prone to leaks due to the design but can be made to keep the oil inside.