Darkvader
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Yes! It’s all a bit confusing because i’m muddling through learning and trying things. Your advice in that post doesn’t seem to apply as hard touch doesn’t seem to work for my carb though thank you for trying to help :). I didn’t realise there were different ways that it could be done and the potential minefield with how things are measured. I’ll make a post on that thread to come to this post. being that they’re kind of the same thread.
I’m certainly closer now than I have been before, either i misunderstood an instruction or I’m just a donut in that previous post and didn’t check that the float wasn’t getting bound up (which is what happened for me to have to change that rear one). It also didn’t help that I didn’t have a huge amount of time to make sure before life whisked me away. This last week i’ve managed a lot more than i’ve been able to and I’ve basically had to start from scratch.
I’d also rather document all of my misadventures so people don’t make the same mistakes I do.
What I’m considering doing is making a carb clean and float setting guide once i’ve figured this all out. it’s obvious there’s a lot of difference in how different mikuni carbs do things.I saw the youtube clip, hmmm i can try break this down for ya , follow me, i think i am on to something but will need you to also verify next time you have your hands on it.
- Spray the airbox rubbers and intake rubbers = see if revs change or engine grumbles or screams = air leak. [\quote] I did this earlier and no change (this also applied earlier too, i think my rubbers are good just the carb doing something funky) Also the biggest change to speed happened when putting the bike on it’s side stand, i believe that’s pointing me towards floats (argh lol)[quote]
- Rev up to 5000 rpm then let go, do you see any kind of smoke, do you smell any oil stench on the exhaust ? = too much engine oil , or concern for oil in engine (replace it, if the bike ever had fuel leak out of the carbs when it was OFF)
What seems to happen is the opposite, it will smoke a bit during idle and revving the bike causes it to clear up. I suspect it’s just so rich that the little smoke is actually from being super rich. it doesn’t smell oily to me
- I see you have a full tank, buy WYNNS FORMULA GOLD PETROL (this bottle only) pour all in the tank, ride a bit and let us know if the bike starts to behave a little better as the fuel bars drop low. I trust the carbs are clean already but the WYNNS bottle might also make its way through the fuel lines, spark plugs , pistons ,to get some gunk off and take away some carbon (it will try!)
When i next fill up i’ll get some, currently there’s some redex in the tank :).
Plug Analysis
- Front center cone = main jet is OK, full throttle seems OK, but idling a bit rich due to dark black sooty ring but…..is the black ring oily or ashy-dusty ? – The plug’s threaded body looks dark at the base and almost silver rest of the way towards its white insulator, it means front cylinder isn’t overheating like crazy (thanks to winter and the nakedness of the GV!)
as for being black, it’s like ash, rather than oily.
- Rear Center Cone + Rear RING = OK. Nothing to add here, it’s good! – This is the “aim” or sweet spot if you will.
- However, rear body of the plug suggests its a bit hotter than the front (threads are darker = hotter cylinder head but …. not concerning yet)
awesome 🙂 I’m not paying a huge amount of attention to the colour of the threads at the minute, they’re old plugs and were like that anyhow but i’m glad they not concerning 🙂
Throttle dipping / climbing means either these but we will narrow it down as we progress on servicing her…
- Mixtures , try to ride at 2.5 full turns out each cylinder and see how it generally rides. This will be our base as going beyond 3.5 turns is totally pointless , it will have less effect once you in full throttle (main jets and “slides” take over) so full throttle issues should be jets and slides (sticky?) …) or floats or fuel pump wanning or tap wanning , or the fuel parts have debris hence Wynns Formula in petrol to collect em and engine to burn them off out of the exhaust
My GV has 17.5 sized pilots, currently they’re both at 2 front and back. I wonder if the rear cylinder is a touch too lean at idle and needs a quarter turn more, and the front a quarter turn less.
- Pilot Jet clogged again (revs flactuate) is a sign its “hunting” for fuel to prevent the bike stalling abruptly
- Starting = Permanent Jet + Pilot Jet = If you get access to air compressor , blow them hard
When cold the bike starts super easily, it’s actually harder when it’s warm
- Fuel Levels = float heights , pilots “barely” reach the fuel but i think you know how to adjust them to a sweet spot by now 🙂 or i understand you’re experimenting with fatter aftermarket floats vs OEM ones but they still have max resting height of 7mm-8mm max . 7mm is the OEM sweet spot, i understand float needles and what not can affect the height a little bit , too much here or there can overflow fuel out of the carb so adjust and check accordingly.
- Richness = revs up, then dips below 1500 (see what i said prior to this sentence)
i’ll double check the floats, maybe my calliper is more a callipo than a mesuring tool lol
- Needle of the Slide = If it has 5 steps to go down to the pointy tip, try step #5 , if its worse, go up to step 3 which is its default middle setting but never go beyond step 2 and 1 as those will lean out the bike. 5 step or 3 step needles Korea uses are always at the middle setting from factory. Going to the middle lets you see if full throttle makes it hit 70mph or not. More speed more fuel or too much fuel can bog it if rest of the bike isn’t optimized (air vs spark (all electrics from coils, plugs etc,) vs fuel (carb, tap, pump)
the front cylinder from stock is 4 and the rear being 3. I’ve left them at stock but maybe with the new jet it needs to be dialed back a touch on the front.
Full service is not a bad call! – You want to get to it before it gets too cold and Xmas is around the corner where families rob our time until new years lol I hope this reply made any sense but if at one point i confused you, just let me know , ill explain better next time
I’ve made a start on a service today, I’ve changed the Oil and filter. I also used the time to fit a 250 oil cooler 🙂 my oil lines were getting a bit frayed and looked quite rusty so it made sense to change them and do an OEM plus upgrade 🙂
I have yet to do the plugs or look at the mixtures. but I have a few jobs under the tank as well that when i have more light i’ll lump together.Honestly, i really like the stock look 🙂 i’m not one for the bobber style.
I was out earlier today and while it doesn’t feel any quicker (and still seems to get stuck at 60mph) the plugs are nice and tan. there is still a weird idle issue, revs will climb a bit to 1800, then a blip of throttle will take that down to 1200 but I think that’s more on the mixture screws than anything as the idle isn’t unsteady it just seems to want to climb a bit for some reason.
Here’s a video of it running https://youtu.be/u4JYxObujJs
This is the front plug:
This is the rear
Next job will be a full service, oil change, new plugs etc. 🙂
Thanks for the youtube clip; I can see your confusion there…
- Did you already use a new rebuild kit ?
- Did you use new floats from us , as they are factory adjusted?
Oh that’s interesting, I wasn’t aware they were factory adjusted, yes i did use new needles and seats. I used the original floats at first, mostly to get a feel for how to adjust them (and this is more a learning project than a by the book thing anyhow) but I will swap in the new floats.
7mm = This is when the float is actually resting on the “needle” plunger (If you press down the float, it will drop to 4-5mm ish) The spring is just there to make sure bumps , shocks , etc doesn’t cause the float to ram the needle against the golden seat (well) 17mm is when the float is lifted up to the ceiling (as that would be how the carb is when it’s on the bike) , until the float bowls fill up with the float going down to 7mm to close the fuel delivery. (it will hover around that number as you ride as not to completely drain the carb in full throttle)
This is what I was thinking when I started but i didn’t adjust the floats so they may have been set wrong (and i was using the originals) when I first tried.
Then I asked earlier for some clarification and ended up gooseing it up completely with the hard touch thing that someone else said. I’m sure there are carbs that are set that way but obviously not the bds26.In the video i set the height to 7mm soft touch and with the original floats. I reassembled it and managed to get it started but the rear cylinder was sending fuel out of the breather. I quickly changed the float and it’s now happier, with the original on the front cylinder and the new one on the rear. it actually idles rather nicely now, revs don’t hang and quite honestly i’d say it’s about where it needs to be but it still seems quite rich at idle. I’ll change the front float, it’s probably that which is still causing my grief.
Thanks for being so patient Marcel (and everyone too).
Congrats on your test! Stay in the hyo family lol. Keep the 125 for winter or short runs as i own one myself for just that or as a work horse sometimes (if car isn’t being used haha) , but keep an eye for a GT650 or GV650 🙂
Yep, i’m keeping the GV125 :), i’ve been keeping an eye on that Japanese GV250DRA something about that tickles me. obviously if a 650 or st7 comes along i’ll seriously consider that too.
On your GV125C – Few pointers if it helps;
- Float height 7mm sitting down (means float is gently resting on the needle) , 17mm lifted up… But 8mm is a generally a max limit when the carb is sitting on its diaphragm covers.
this has confused me slightly, though I think it’s more about the terms used. Would you be able to walk me through how you measure things?
I have a little video here https://youtu.be/lwInsUauWfc
in this video i have the float set at 7mm with a soft set on the diaphram covers. before this I tried a hard set, with the float at 7mm and the spring fully compressed so maybe like 10mm with the spring.
I assume as well the 17mm is the maximum open drop on the float, i measured 14mm earlier but i may have this completely wrong.- Tank Tap = Check OFF means OFF (Disconnect the hose safely and ensure the tap still doesn’t leak out fuel when its in OFF mode)
- Change Floats = If in doubt about them
- Change “Needle Seat” and “Float Needles” , these 2 are literally the only items that will stop the fuel coming in after the floats have risen (extra fuel will just overflow to cylinder overnight sometimes) – Hence “float jamming” being a common thing on carb motorcycles , it just means we have to extra be serious with them (unlike injectors lol)
140 psi via a flexi hose should be OK to make it “start” at minimum, the hard metal pipe is pushed down as we crank the engine or it shoots at you!😉 (Just make sure the metal bit uses a Spear Shape rubber tip.
I tried the metal pipe one first, I made sure to get a tester with it, sadly I got worse numbers as i just couldn’t get a good seal even going full hulk. I think i must just have noodle arms though.
I actually reckon that the last time i adjusted the floats I may have set them too aggressively as I had a feeling the needle would bind up. it didn’t seem quite rightSorry for all the potentially stupid questions, i’m just doubly making sure.
Thanks Marcel.oh forgot to say, I didn’t get the engine hot for this test, it wasn’t idling properly at all but with the raw petrol being shot out I reckon if i pushed it i would have caused some harm.
Hello again! Sorry for the delay. I’ve had some other bigger focuses come out of nowhere in the last few months so I haven’t had any time. On the plus side I passed my full A licence test 2 weeks ago so the L plates are off.
I did a compression test earlier today and i can confirm both the front and rear cylinders read the same value of 140ish psi. I had no luck with the hard tube but the screw in hose worked well enough.
Now here’s where things get interesting. When I pulled the plugs and before I ran the test i spun the engine over for a split second and it spew out a considerable amount of raw petrol out of the cylinders. I’m amazed it didn’t hydrolock! This now means that there’s something else going on. It would also explain why the front cylinder wasn’t firing, it was probably getting fouled something chronic.
So my next bet is to pull the carbs off again and re-do everything. float heights etc. Plus change plugs and do oil again.
Knowing I double checked the floats and seats before i tried getting the bike running i’m surprised but hey at least the bike has good (consistent) compression.
Any further advice would be useful. Thanks again!
🙂 i did thank you, hope you did as well! I sadly didn’t get chance to try sort the bike again but I did manage to sort the garage out, so when i next have a chance it wont take as long to find things.
I haven’t yet got a compression tester but I’ll be ordering one shortly, hopefully by sunday next week i’ll have had a chance to do a compression test.
I’m not sure if i’ll be able to idle for that long but what i can do is have a quick back and forth down the road if that works? it’s quiet here so aside from the strange looks it wouldn’t be a problem if that’s better haha.I’ll update you on the measurements when i get chance to do them
Thanks Marcel!oh i need to elaborate, At high speed the front cylinder does come back and will run perfectly, but throttling off will cause the bike to rev hang. Also the bike doesn’t surge at idle, it just seems to not want to fire on that front cylinder (doesn’t get as hot)
i pulled the plugs after a ride and the front cylinder has a light tan to it and the rear has a moderate tan, basically perfect… if it wasn’t for the idle issue.Thanks everyone!
I set the float height today, it’s a good job I decided to bite the bullet and do it again, not only did I originally measure it wrong but I also discovered the seat needles in the rebuild kit are ever so slightly shorter with a bigger spring.
I actually found a tool that i already had that did the same thing, a tyre tread depth guage. that measured 4mm that i had it set at after my first rebuild. it’s now running more sensibly. the cold starts are a bit hit and miss still but I think that’s pilot circuit related, it still seems to run lean at idle (revs gradually climbing +150 rpm over a minute, then coming down after a blip of throttle).
Yes, I had a look at my 650 today, the set up between the carbs is quite a bit different, there’s quite a lean on the carbs (towards the front) for a hyosung, which i imagine can change how the floats operate a bit, i wouldn’t mix and match too much but useful to know there’s some knowledge that is transferable :).To be honest, I’ve been eyeing up making up an electric pump conversion, i’m still having issues with the pump on mine and that’s after 3 cleans AND completely new vacumm lines. I’m thinking a 1psi electric fuel pump (looking at the setup my my xvs650, one of those pumps \could potentially\ work, the pressure switch for the pump is built into the pump itself), small relay, tilt switch, fuse and fuse holder and three wires. I’ll have to experiment, that vaccum pump is making me go mad :P.
The (above) “wet”-test is the best. The manual can be confusing, but the 7mm measurement is on “full/hard-stop”, – spring compressed. Most often (on other carbs) measurement is on “light-touch”.
oh, that’s news to me! that would be why the measurement threw me. thank you 🙂 Guess i’ll have to pull the bowls off and get that float set correctly again, will also give me an opportunity to rejet too, i’m still rocking the 82.5s.
that’s a handy little tool.Oh and i found this from the service manual for an XVS650, which has the same carb type. I would have done this but i didn’t have any clear fuel hose.
Thanks marcel, I wasn’t sure if it was mentioned before and i was a little surprised finding such a small jet though i’m also not surprised knowing the emissions people.
I’ll be getting a 85, 87.5 and a 90 pair and playing with some of the settings for the slides as well. it seems that mine from factory had one slide set at 4 and one at 3, i’ve bumped both up by 1 (richer) but that may be a bit much. either way, it starts a load better now i’ve cleaned everything.
I’m not really planning to put a bigger exhaust on the back, i quite like where it’s at currently sound wise. Living in a quiet area i would rather not bring attention to myself, I may put a few small holes in mine if i fancy something a bit funkier, i’ll see :).
Sorry for jumping on this post but i thought i’d share what i’ve found in my carb today. Mine is a 2012 GV125c and has
17.5 pilots with seemingly 82.5 mains.
I was expecting 87.5 but it seems to read like 82.5.
Am i misreading the numbers on the jet?
Thanks Guys.Thank you,
I managed to find a collection of them on ebay: Ebay Link Here
I’m not sure how long they will last so I will let you know if the heat will break them down in a few weeks. failing that you could get some vaccum hose, fold it over and use a cable tie or similar to tie the end off. It’s not as neat but it will work if you can crimp down on the hose tight.
I wouldn’t say it affects the performance that much, it just makes the bike sound nicer and removes all those hoses for doing other work. I’m going to be pulling the intake boots off next week or so and being able to work around them without a million hoses in the way is quite nice.
- Both Plugs = Slightly overheating… (((With oily deposits on threads????)))
- Front = leaning out at high throttle
- Rear = leaning out too but seems to do better than front.
- Both Plugs = idling OK. (Assumes mixture is 2.5 front and 2.75 rear using size 15 Pilot Jets) but see next bullet point….
- The carb needs to have its jet needle at a richer setting as the white cones need to be brown after full throttle runs.
- Mixture screw will have less effect once the carb slides & main jets take over at past 4k revs. BUT it does have an effect during gear changes as bike momentarily lowers revs or coasting while rider carefully disengages/engages clutch to change gears. The carb slides then lift off again.
That oily stuff is copper grease thanks to my uncle. I know it’s not always needed but Me and my uncle had a bit of a fight getting the old plugs out so when i started on the sprocket he plopped them in. It may actually be overheating worse, there’s only 160-180 miles on those plugs.
I’ll be pulling the carbs off when I get my cleaning liquid for the ultrasonic. I’ll leave the settings as what they were, do a couple of full throttle runs and see how much of an improvement. I fully expect i’ll have to clean the carbs two or three times to get them right, they were sat a LONG time.
I’ll drain the tank and have a look over the tank and tap again. When I fitted it (it is new) flow seemed OK but it was cheap and i’m sure that the most expensive stuff starts cheap lol.
I’m going to do a guide for a few things, I like making documentation. I will take some photos of the airbox when it comes off. I’m really trying to mentally prepare myself for it, i’m not quite ready yet to allocate a day to it.
As for cam chain noise it doesn’t actually get worse or better, it’s consistent. really I was just wondering if it sounded ok.
I do have a suspicion the clutch is on it’s way out. I believe it’s the original and the biting point seems to like to wander. it also seems to stuggle to disengage some times. Maybe the oil i put in before I started work is just rubbish (Motul 5100 semi 10/40 i think).The heads get a little more clattery when hot but it doesn’t seem to get worse under revs. I’ll use the screwdriver trick to listen to the tensioners. The video was the bike when it was hot/hot ish.
Thanks again.
Hi Marcel, I went for a little ride earlier, nothing particularly taxing and these are some photos of the plugs in question. sorry for not getting completely top down on it, I just couldn’t get a good focus. I’ll have another stab at it when I fit the new coils and stuff (which i got today btw! super quick)
1. Rear Electrode 2. Rear Thread 3. Front Electrode 4. front thread
From this I can easily tell the front cylinder is running leaner than the rear and the rear is still a touch leaner than i’d have thought it should be.
I didn’t get any measurements of the head temps, sadly. they were both equally hot to touch when i stopped. I couldn’t find my thermometer before the bike started to cool down for any numbers though. I’ll take them tomorrow.
I do have some videos though, One of the fuel pump and two for timing chain.This is the idle noise video. I do hear a slightly metallic sound somewhere.
https://www.youtube.com/watch?v=vkNrRK57OgMThis is a quick rev
https://www.youtube.com/shorts/k9R1RwjsWSg
and this is the fuel pump
https://www.youtube.com/watch?v=B8JATX56ld8
Hopefully this helps you narrow whatever weird gremlin seems to be posessing my bike at the minute.
Thanks MarcelI’ve sent another reply but i believe the anti-spam/system has caught my message because I also added some pictures and video links for how it runs for any noises and the fuel pump.
Just in case that was a problem both cylinders are hot, they’re both obviously firing but the front cylinder is obviously leaner than the rear, it’s squeaky clean white. the rear has just a touch of tan. Obviously the carbs haven’t been off yet but it’s interesting to see how lean it’s actually still running with.
the threads on the plug don’t look very hot at all, there’s a band of black around the first 2 threads, gradually tapering down to normal metal colour over the next 3 or 4 threads.
thanks again MarcelNo worries about things not making sense thank you for replying so late. I used to work in IT and you’ve given me heaps to go off, making sense of ramblings I got quite good at :).
- Fuel Pump wanning (happens, carb cleaner sorts it when you take it apart CAREFULLY) or as pre-caution, replace with a new one if you want us to get it.
- Fuel Filter Clogging or not flowing fast enough (if its OEM)
- Fuel Float Level low (repeated in service manual too) (check floats are on a good height, as fuel goes low, then the jets won’t reach , due to pump & tap not replacing the fuel fast enough = high revs . high speed , more demand)
- Carb Slides wanning.
- Carb Slide needle may be on the lean setting (sent 1x needle for free, just incase one of yours is bent too)
- TANK TAP , wanning = Common.
I am suspect of the fuel pump, there was green thick petrol residue inside it (which i noticed when i did the fuel hoses before I ran the bike) and I have already had it apart to clean it. I didn’t exactly think the pump was bad but the rubber did seem fairly firm. The fuel lines and filter were the ones you supplied so I can comfortably rule those out. I am questioning the vacumm hoses, that is the next job on my list though, they are the original ones and if there’s a restriction or leak in those hoses that could stop the pump working at high demand too i’d imagine.
I will check floats and slides carefully when I have the carbs off, I keep reading 7mm for the floats on here so that’s well in my head now. Thank you for the needle 🙂
I am wondering about the fuel tap flow rate, I fitted a new one on my tank that was a cheap chinese one and it may be more restrictive than OEM. though it does flow freely when opened and it’s the same design as on the yamaha i have (which is a 650). I’ll drain the fuel and see if the tap is giving a bit more of a restriction than it was when I fitted it. No big loss needing another tap if so though, it was a fun gamble.
One thing that comes to my mind, how does the vent in the tank work? is there a check valve or so? I’ve seen fuel issues before (in my car) where a restriction in the venting of the tank will stop fuel flow as there is a vaccum being built in the tank stopping the pump working.
I will go for a little ride tomorrow and read plugs and head temps when i get back.
Normally , when a hyosung that is all OEM and negelected (either by garage or last keeper) , the carby 125 ones at least , they usually spend their lives in the city with a max of 40mph runs , then owners use crap service parts on them to keep em going, but never touch the carbs , or do engine clearances (valve clearances do eventually get too tight , being a hot engine doesnt help) , never changing air filter….
Clearances are next on my list too, i know when things get too hot/tight it can bump a valve open slightly and cause a loss in compression/power. I don’t think I have the skill to do them myself though so i’ll have to book in somewhere.
I’ll send a reply tomorrow with photos of the plugs after a 2 or 3 mile run 🙂
Thanks again Marcel.
Of course, At the time I didn’t have to restart because i was trying my best to keep rolling with the bike in gear. it was completely not doing what i was asking though until it came back at about 30mph, then was fine the good 5 miles back home even at 60mph, like it had to cool off for a couple of seconds.
It’s always had little starting gremlins though, when it’s cold it’ll fire up, then come and go for a few seconds and i’ll have to rev the bike for a second for it to start being happy to run, even on choke, i put that down to carbs originally but i’m not sure that’s the full picture.To be honest it’s never been jerky or juddery, yesterday it was running fine the only thing i can see directly that’s a bit weird is the tacho being jittery at 8-9k. I’ve not had a flat battery or anything because i use a battery maintainer though the thing that made me think electrics is that the original owner had put a new battery in after a year and i’ve had another new battery (though i think that was more frost, we had a bad winter that year).
The engine feels completely smooth at the speed i was doing, it was holding well but the needle will go from about 9k down to 8k in like a uneven flicker over half a second or so. plus when i was stuck at 50 the needle was doing the same thing, even though normally it wouldn’t at that speed. I’m puzzled.
I’m not so much blaming the boots or coils as such but I’ve ordered them as well being that i would like to run the laser iridiums properly and I like having spares.
What i’ll do is i’ll hook up a camera to the bike and record how it’s running, try and get the speedo, tacho and the engine note for you, perhaps your trained ear will help.
Thanks Marcel.
