Jetting a GT125R – 2017 ..?
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I have the GT125R-2017, bought new a year ago, as new overlayer(3+ years!!) Went thru the run-in-process last summer, then fitted :
BlackWidow system; pipes & muffler,(loud, even with largest can); https://www.blackwidowexhausts.co.uk/hyosung-gt125r-gt125-comet-full-exhaust-system-400mm-round-silencer-1295-p.asp
K&N air-filter
+ re-jetted with 6SigmaJet kit; https://www.6sigmajetkit.com/hyosung-gt-125-r-s-comet-jet-kit.html
– now with the largest jets: F-95/R-97,5. (Bowl-Level checked ok, dry, and wet). Still running lean…????
Sparkplugs are still as white as new.I can get a GPS controlled 70+mph (with ”520-upgrade” DID-VX3 & JT-13/46t) = good enough, but there are no power/torque at top-end, (feels lean), drops speed (and rpm) as soon as you can see the road rise upphill, or god forbid, I meet wind…
Bike is ”almost new”, just round 500 miles total, (have changed oil/filter 4 times, (more than needed), but the almost black oil I emptied out after the first 50 miles scared me…been better thereafter).
Shinko-Tires swapped to Bridgestone T32 front & Michelin Road 5 rear.(stock size).
(Tried NGK Iridium Spark Plugs; DCR8EIX – no change)Back to question: Lean? Not enough fuel supply? Or should I just try even larger jets?
Suggestions, please.
regards
Arne
-any/all spelling-mistakes are dedicated to my teachers…I’m Norwegian…BTW, had a 2014 Honda Varadero XL125V -3 years ago, similar weight, had more power, (watercooled & injected), but no stability compared to the Hyo…
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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Before we get to the parts, it is still under 1000 miles old, so its very much in the “running in” stages
Around 600 miles , it is mandated for dealers to;
– check valve clearances (must be checked otherwise tight valves or loose ones will have a domino effect on peformance to the engine, carbs, etc..)– Compression Test (very easy) – must be sure the pistons are putting out correct PSI after it has warmed up,
— Warm up engine -> then remove plugs (both of them) –> crank bike for 5 seconds max –> read compression.
Repeat again for rear cylinder tooLet us know the PSi it is doing
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Compression-test: 12,5 Bar (F & R) = 175 psi
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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Compression-test: 12,5 Bar (F & R) = 175 psi
That’s very very good!
Is this when engine was hot? and both spark plugs were out?Can you wait overnight, wake up in the morning and get service manual, open top valve covers.
Get feeler gauge that is in “.mm” (0.05mm to 0.40mm)And let us know clearances for each valve? Dont do this when engine is warm, it must be overnight cold.
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It was not hot…but warmish…(they should have made a hinge on tank and oil-cooler, & quick-connects….)
BTW, compression was checked with 2 different meters (read identical). -both plugs out, and 1/2 throttle. (Had a long screwdriver stuck in the carb to keep it open)
Will do valves as soon as time permit.
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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Todays conspiracy: How-come even japanese-made feeler-gauges are made of recirculated British steel from early 70’s?
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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Todays conspiracy: How-come even japanese-made feeler-gauges are made of recirculated British steel from early 70’s?
The Japs & the brits got a little cosy during war days and they both fought wars (to each other and to their enemies) expect them to know how to both work the steel/metals for whatever instruments they made. But ofcouse im going off-track on a bike forum , history is wishy washy so i dare not digress haha
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Clearances are spot on; on both cyl, intakes, a .010 slides in, a .020 dont. and ex: 020 slides, 030 dont.
However… the plot thickens …
Seeing the camshafts, I noted a strange difference… and checked with the manual. Alignment is off! On rear cyl, both index-markers points straight up, and not to each side… (see pictures !!!) Front:
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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Rear: (with the magic of mirrors, I could just see the lines pionting up)
The way the cams pointed up/inwards, alarmed me to check…
No wonder there is a lack of power…actually a wonder that it did as well as it did.
This seems like a factory-error?
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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The cams on the rear face up but torwards each other.
But look at the edge of the cam shaft bars and make sure the dark black _________ line is on the same level as the surface of the cylinder head (where rubber gaskets sit)
Both cams must be equal ________ marked to match the surface of the engine gasket area.
Also if i remember correctly (it’s 10pm, so my brain is a little funny!) , the #2 on the sprocket is 100% facing straight up | ^ to match the cam cover holder bolt thread.
#3 on the sprocket for the intake is facing UP but it will be like this / than | straight up
Spin the crank 10x to be accurate and recheck feeler gauge for clearances.
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The index-lines I refer to are the (faint) line at cam itself (not the sprocket). Should be like circled in green, mine are close to the red line… The sprockets align (blue circles).
Cams are correct placed, IN/EX marking between lobes. Cams are bolted in similar to picture…
Will maybe bolt on a degree-wheel to crank and check timing figures tomorrow. Front & rear should however be the same… -and they are not.
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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Seems the outcome is the same… why did they not print the lobes like in the 650 manual? -would have saved me a lot of time… -see pic…
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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But…talking about lobes…intake cam is pretty mild. If i had plenty of parts, to experiment, I would have tried the 250-intake-cams.
Back to jetting. Seems I need to save up for a dyno-session, or a wide-band lambda.
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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Dyno-result: 13,2Hk/10 000rpm – at rear-wheel, translates to 15Hk from engine.
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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13.2BHP at wheel? If that’s the translation ?
What modifications were on the bike to achieve this ? This may be useful for future owners to keep an eye on this thread , it is interesting. I don’t know too many people in UK who have taken their bikes to DYNO and published results online (especially with everyone trying different mods on the bike)
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Mods:
K&N-airfilter
BlackWidow exhaust & manifolds (largest round can with “dB-killer”)
EGR-delete
Honda Rectifier/regulator
520 chain/gears, with 13/46-tooth. (GT250=14/46)
NGK plug-booths & upgrade coils
Jetting:
Float-level (carb upside-down): 7-7,5mm
Front: 95 Rear: 97,5 (Proper jets from 6SigmaJet-kit) Pilot: 15 (stock). Needles at upper level/clip at lower.
AFR was very stable at WOT , within 12,5-13,5 from ~4500-11000rpm
I had hoped to find another pony or two, but the butt-dyno thinks it may be less than one…hard to say without a dyno-test as bone stock…
I also need to find a better silencer, acceptable under 6k, but gets LOUD at speed.
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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Dyno-session
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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DB Killer = Remove it, and hammer the tube inside of DB killer so that “hole is smaller” (about dimensions of 10 Pence UK coin)
This means less gas leave bike
Better lower end torque (very tiny boost) but DYNO will notice.Also Jets 90 and 92.5 are most optimal . 95 and 97.5 is a lot!
Then try DYNO again 🙂
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I already had filled a handfull holes in the “dB-killer” with pop-rivets (just shy of half the total holes). Not much difference. I guess the muffler is sized for much larger engines.
BTW, if jetting is right, NO (4-stroke-) engine will ever make more power with restriction in the exhaust-system.
Part-throttle/mid-range can change, due to cam-overlap.
90/92,5 was on the lean side with stock muffler (lightly modified) and BlackWidow pipes. On MY bike…(with the mods earlier mentioned).
I do not like running AirFuelRatio in 15+numbers at high rpm-wide open throttle…most engines likes AFR round 13 for best power,-also to control temperatures.
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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The changes to the stock muffler: De-cat, + removed inner (smallest diameter tube) from outlet.
With / without cat. Needed a lot of elbow-grease to get there…
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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The outlet… cut the tube loose, divorced inner/outer tubes, welded the larger back. Gives enough sound so you don’t hear the gear/chain, but the engine.
I can live with the modified muffler, but it still is much too heavy. (Living by Colin Chapman (Lotus) famous words: “Simplify, then add lightness”
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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If the jets are 90 and 92.5 with slide needle on rich setting, with K&N air filter (K&N 6507) and Lextek OP1 exhaust muffler and Black Widow Exhaust headers
The 125 tends to pull the best (acceleration wise) , this is also assume the mixture screws of carb did not get touched.The Pilots can stay size 15 forever. When you remove DB Killer, bike runs leaner and screams louder but has a slower pull through gear , the only real gain is the top speed (maybe 1-5 mph extra at best)
The OEM Hyosung stock can (muffler) is very heavy and it is quite taxing for the 125cc (not really a problem for 25occ) but lightness is important to the 125cc indeed
If i use 92.5 and 95 on a customer bike, that would be maximum tube because of using NGK LASER plugs, they are a nice gold brown colour . Having a 250 cooler helps a lot too. You may be surprised how heavily used these 125s are in the UK (for work ride, for pleasure, and general riding to cities this is everyday)
Also i have advised some owners i work with in person to stop using E10 fuel, it is rubbish. Nothing positive about extra ethanol mix. So we use e5 and the bikes like it. (E0 would be ideal lol)
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We still have 98 octane (without “E”)… -the 95 octane may have up to 10% garbage in it. Ethanol-mix is not for engines… not even good for the environment.
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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I did uprate oil-cooler last year, but I think the 250-cooler takes away much of the access to front spark-plug, so while experimenting, I found a cooler just in between the 125 and 250.
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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I see the ebay version has 1 less row , not too bad , where did you did you get it from ? I may experiment with it as i usually put temp sensors and gauges near the cylinder heads (custom work) to stay paranoid lol.
Did the ebay one fit straight away ?
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epay unit fitted within same top-bracket, same hose-coupling. (it did have an additional bracket on the underside…hacked away on picture. And it was raw-alu-color, I gave it a dash “radiator paint”)
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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Have been tuning the carbs a little more…for drivability, response and low-rpm “cruise”. And can not understand the “religious” view of keeping the stock “15” Pilot-jets…
I had to raise the needle to lowest clip-pos. + add a small shim (~0,2mm), + increase Pilot-jet to more than “30”, and less than “40” -still some finetuning to do, but will end up with Pilot-jets @ ca “35-37,5”. – Makes the bike rideable in the 2,5-4000 rpm band without issues.
A wideband O2 has been a good help.
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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At pilot 30’s , what is the mixture on the carb how many turns is it ?
It could be your climate and altitude where you live at , but here in UK , 15 pilots on the 125cc is the gold standard. The 4-7k rpm flat response is improved by ofcourse fine tuning the slide needle with larger main jets (1 size up front and rear main jets)
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Well, carbs & jetting…changes all over the world…based on temperature and air-pressure/height above sea…
I’m located “sea-side”. (South-west-coast).
With 15 and 20 jets, and 2,5 turns out, it would run, but the “needle”-screw did not give much response, could turn a full revolution in before it stumbeled, and died. Could also turn a couple of turns out (from “ideal”) without change in rpm. With 30 jets, it started to respond on the screws, still best at 2,5 turns out, with 40 jets, response was good, -best at 1,5 turns out. Idling with AFR=14,5/Lambda 0,99
Many good hints on jetting here:
https://pilotodyssey.com/BillGivensjetting.htm
(40-pilot-jets actually came in the 6sigma-jet package)
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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The BDS26 carb has ability to power even a GS500 or maybe an old suzuki i4 (inline 4) with 15 pilots (up to 600cc maybe) , but 30 pilots ? Even the carb 250cc Hyosung is perfectly fine with 20 pilots it uses, mixtures on the 250cc would usually be 3 turns or little less from factory.
Not ideal i know. All stock carb bikes can be tuned 😉 – – If the 250cc (250cc?) can live with BDS26 carbs and same airbox & same air filter, i don’t think a 125cc will ever max out the capacity of the carb, so factories fit smaller jets. And sometimes downtune (downgrade?) the carb to meet 14HP laws in some countries. & emission control (Euro 3 crap)
However i do KNOW , using 250cc intake pipes on a 125cc engine helps with throttle response! (250 intake pipes have a bigger hole) and is much shorter , so carbs are much closer to engine with less travel around the manifold bends for air.
The 250cc airbox is required for this but its okay , its a little deeper than 125 (more room inside for air)
Have you perharps tried size 17.5 pilots ? and check your spark plug colours (from new or fresh clean)
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Todays color…after 1 hour city-riding (slow), = white…
I have “touched up” the rear intake. Fuel-injection / micro-squirt, or similar is tempting, if I can find the funds…(and cheap parts).
The reason for larger jets, in a smaller engine, is the “signal” the carb gets is smaller. Same carb on a Harley, may be way too rich…
And pilot-jet size is mostly (by factory) determined by emission. I tune for drivability. My little contribution to a warmer world…is less than what comes out of a pigeons back. (Yes, tried 17,5, and 20. still too lean; evidence: when you can turn mixture-screw a full turn in or out from “best” setting, and engine-rpm changes less than 50-100rpm, jet is to small. Same rule goes on a 2-stroke, a 2,0-SOHC, a 5,0-V8, and so on…)
Have you heard the story about the farmer that tried to change his horses habits? After a couple of months, he was devastated, all the horses died, and worst of all, it was just before they were “rehabilitated” to not eat at all. So close… 🙂 .
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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Todays color…after 1 hour city-riding (slow), = white…
I have “touched up” the rear intake. Fuel-injection / micro-squirt, or similar is tempting, if I can find the funds…(and cheap parts).
The reason for larger jets, in a smaller engine, is the “signal” the carb gets is smaller. Same carb on a Harley, may be way too rich…
And pilot-jet size is mostly (by factory) determined by emission. I tune for drivability. My little contribution to a warmer world…is less than what comes out of a pigeons back. (Yes, tried 17,5, and 20. still too lean; evidence: when you can turn mixture-screw a full turn in or out from “best” setting, and engine-rpm changes less than 50-100rpm, jet is to small. Same rule goes on a 2-stroke, a 2,0-SOHC, a 5,0-V8, and so on…)
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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I don’t know about you but damn , that white center isn’t good, it suggests bike is leaning out full throttle.
Here is a picture of an old customer of mine , his bike as factory brand new. He did not touch anything and he is the only owner.
The carb was 3 to 4 turns from factory , standard jets, everything was standard on the bike. No mods.
It was annoying to start in winter sometimes.
Threads of spark plug is a bit yellow ish = engine hot (a tiny bit too hot)
oily threads = crap gasket inside rocker cover.ARCH of plug is okay = piston chamber heat is okay.
Center is brown ish = seems okay full throttle
Circle Ring is black, sooty = rich idling.
Next below is one of my old laser plugs. I was OCD with the bike , i got a little obsessed with trying to get an “ideal brown color” on the plugs.
These plugs are 2 years old.
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Agree, your plug-example looks about right.
About mine; this was after 1 hour “city”-driving, never above 6000 rpm, never above 1/2 throttle.
(mixture gets richer at wot, and higher rpm)
And…please delete the double-post, probably had a browser-glitch…Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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