GV250 Won’t run after carbs serviced!
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I have serviced the carbs and had them ultrasonically cleaned, but the bike won’t start. Won’t even try!
Alan advised me to try getting fuel directly to the carbs in case there was an air lock or pump not functioning.
I tried that but the float chambers were actually full! So I tried something new – I left the “choke” off, and because that is only a fuel enrichment device, I closed off the air intake with tape, and guess what, the bike started and idles beautifully – BUT you can’t do anything else!! Touch the throttle and it stops, open the Choke and it stops, take the tape off the air inlet and it stops!! Unless anyone has an idea I’ll have to take the carbs off again. Perhaps the stub O rings came out. It’s obviously getting air from somewhere.
The only thing I forgot to do when rebuilding the carbs was to put the very small seals on the idle jets. These are new ones from the store, and I have 92.5 and 95 main jets, front and rear, and adjusted the mixture screw to 2.5 turns out as per your advice.
On the off-chance that someone has had a similar experience and I’ve missed something obvious, I’ve posted this.
HELP!!
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Hey,
When you twist the throttle and it dies, it means either:
- The “Throttle Slides” are not lifting up to release main jet fuel to combustion chamber as the bike revs up
(Sticky or torn slides even so much as a small rubber rip?) - Spray “Carb Cleaner” on the intake rubber pipes connecting the carbs to the cylinder heads = if revs change, there is a leak there.
- Airbox issue ~? (either the top one or the right side one)
If you have size “20 Pilot Jets” I have sent you , that should be inside the carb already (I assume cleaned from any packaging dust?)
How fresh is the fuel ? (Assuming it is E5 grade or better)
Next time it runs, twist the throttle very very very slowly and see if revs rise up?
- The “Throttle Slides” are not lifting up to release main jet fuel to combustion chamber as the bike revs up
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OK! I decided to do a more exhaustive check (no pun intended!) and after starting I let it run for a bit to get exhausts warm. Front warm, rear COLD! I have a spark so must be carb or airflow. So I’ve pulled the carbs off (easier 2nd time!). The stub seals were perfectly fine, so I’ve stripped the carbs again and thoroughly cleaned and blown through. In the kits you sent there were 4 seals as per picture, and I don’t know where they should go. Can you tell me? Should there be anything on the idle jets? And what are the brass bits arrowed? How can they be cleaned internally?
Happy hols!
cof 
cof 
cof -
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Because the carb has orings inside the throttle shaft, choke plunger, valve float seats, there were extra freebies incase you did a total disassemble of the carb to pieces!
In this case, you can just keep them as spares for future. I just throw in as much as i can in the gasket kits.They look good! They don’t need orings those Size 20 Pilot Jets. Just a very clean hole, as by now you have seen how tiny the center hole is!
(Sorry we can’t use more than Size 20 pilots as even size 25 will make it run very rough and too rich.)
Size 20 will do for now 🙂“Starting Jet” = Permanent. Must be air compressor as hard as possible as the that permanent jet has an even smaller hole then the pilots.
Funny enough, it is also needed when the bike is running, as heaven forbid the bike stalls mid-way through a journey, it will help you start, it reaches furthest in the float bowl, also has an exit on the sides of it (deep inside the carb)
Here’s a hint,
Get carb cleaner & attach a straw to it (they usually come with one)
Spray inside the “Starting Jet” , you will actually see the carb cleaner squirt out of it deep inside the carb’s silver walls where the “Starting Jet” sits on. Hard to visualize , i know but it will make sense when you try it.
Then you know the starting Jet is not clogged anymore!Oh I forgot to mention that revs didn’t change and engine stopped as soon as throttle touched – not surprising with only one cyl going! Fuel. I have no idea what E5 fuel means. Here in Spain it’s 95 unleaded or 98 octane I use 95
Use RON98 , the more premium the better 🙂
E5 (97+ octane) petrol.Here we have changed from RONS to E’s , so its either E10 (which the hyos hate, old cars hate it, some injected bikes/cars have a love & hate relationship with it)
or we use E5 -
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Sorry to keep asking questions Marcel but should there be a hole in this item (white arrow)? You mentioned a very small hole, but I can’t get cleaner or anything through it, or feel where air might come out, and I’m loathe to refit until I’m sure it’s OK.
cof It’s Okay, if someone falls on to this topic , they will be happy for it and for you for getting this far . Ask whatever you like!
Yes there should be a hole there…. how about this ….
Find in your house, garage or some car store . A wire for speakers.
Strip the wire until you see individual copper strands . Get one single strand , make it straight .
Then poke inside that Starting Jet , if its clear, it will literally go deep inside and stop.
Then get a carb cleaner or “air compressor” rattle can with a tiny straw , like this ……
You will hear a nice hiss down the bottom of the carb
or
if using carb cleaner, as before spray the golden jet and you will see fluid come out on the side of the silver collumn it sits on deep inside the carb 🙂 -
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I’ve buggered up!!I tried the wire and got it down one, but not the front carb, so I foolishly tried a very fine needle and broke the tip off! With heat on the carb body will that brass item come out? And if so, can I get another?
Better still, do you know anyone breaking one that I could buy the twin setup?
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It’s the part arrowed in the pictures above that we talked about, Marcel. Think I’m going to need a new front carb body, if that’s possible!
Send me an email please as usual. I am away for new years but should be back at work this week to check my workshop , i do have some carb bodies but will need to double confirm compatibility for your 250 & the state of them!
Let’s try to avoid spending £500-600 for a new carb with taxes , it’s a lot! However, not Hyosung’s fault, it’s made by Mikuni Japan anyways.
I asked for a picture so that i can see how bad it is and i was praying that your carb can somehow be saved, it can’t go in the bin whatsoever. It’s about to get as rare as Rubber Intake pipes now that the world has gone to Fuel Injectors.
i digress. I am old school. For whatever bike i have, i keep a spare carb to myself or least a full donor bike to myself lol.
Sorry about your day!
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SUCCESS!!! I cleaned carbs again and blew every hole I could get to with compressed air. So I have new needles and jets, new main jets (92.5 and 95), new float valves, new pilot jets and mix jets out 2.5 turns. Put all back together, fitted without air box, filled float bowls with fuel via a tube and funnel, checked fuel out from pump (slow dribble), set choke 3/4 and pressed starter. Immediate start! I can’t get the grin off my face!! Bike seems to rev OK but I’m not pushing it as haven’t changed the oil yet.
All I need now is to get the air box back on! It’s time someone designed and made a new one that can be fitted after carbs. Come on engineers, someone make one!
Thank you so much, Marcel, for all your help.
I tried to load a sound file of engine running but it wouldn’t load. Boo-Hoo!
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Was the sound file an MP3 format or something or did the website uploader give an error ~? – I’m always willing to fix any hiccups.
I am very happy you got her running , what more can i say after all this. And hey no need to buy a carb body now either , just look after your current one 😉
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SUCCESS!!! I cleaned carbs again and blew every hole I could get to with compressed air. So I have new needles and jets, new main jets (92.5 and 95), new float valves, new pilot jets and mix jets out 2.5 turns. Put all back together, fitted without air box, filled float bowls with fuel via a tube and funnel, checked fuel out from pump (slow dribble), set choke 3/4 and pressed starter. Immediate start! I can’t get the grin off my face!! Bike seems to rev OK but I’m not pushing it as haven’t changed the oil yet. All I need now is to get the air box back on! It’s time someone designed and made a new one that can be fitted after carbs. Come on engineers, someone make one! Thank you so much, Marcel, for all your help. I tried to load a sound file of engine running but it wouldn’t load. Boo-Hoo!
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Hi Mike, great to hear you got her running I know exactly how you feel after having to do it twice myself.
Also you will find a huge improvement in performance with the upgraded main jets, I would also advise doing the needle slider upgrade if you haven’t already done so.
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I don’t know what the sound format was, just recorded it on WhatsApp! Can’t remember what the site said, I think it just gave an ERROR and can’t load that file!
How odd, email it to me and ill check it out. If its a recognizeable format, ill flag the site to just allow it from your account. It probably panicked thinking it was a trojan lol
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Hi Alan, thanks. What are the Needle Sliders though? If they are the Needle Jets, I have new ones with the needles. Happy riding!
Hi Mike, this is the link to the tutorial https://hyoriders.club/forums/topic/tutorial-carb-slide-needle-tuning-hyosung/
- It’s an easy process which can be done with the cab’s in situ.
- I had a flat spot at around 4k rpm and this solved the issue.
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Oh dear! Marcel, I am despondent! I am back to running on rear cylinder only. I felt sure the bike would run, even with the front carb starting jet blocked with a broken off needle tip (!!), but it seems it won’t. I have a spark, but only running rear pot. Can you find me a front carb body or suggest anything else I can try. I will send you pics of carbs via email. I have all the new jets already, so can fit them to a body. Hope you can help.
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Oh dear! Marcel, I am despondent! I am back to running on rear cylinder only. I felt sure the bike would run, even with the front carb starting jet blocked with a broken off needle tip (!!), but it seems it won’t. I have a spark, but only running rear pot. Can you find me a front carb body or suggest anything else I can try. I will send you pics of carbs via email. I have all the new jets already, so can fit them to a body. Hope you can help.
No rush fella, I will try to “hunt” down a carb body but due to scarcity they aint cheap anymore even 2nd hand, so expect to spend 3 figures yikes.
I pray its still possible to save yours.
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Oh dear! Marcel, I am despondent! I am back to running on rear cylinder only. I felt sure the bike would run, even with the front carb starting jet blocked with a broken off needle tip (!!), but it seems it won’t. I have a spark, but only running rear pot. Can you find me a front carb body or suggest anything else I can try. I will send you pics of carbs via email. I have all the new jets already, so can fit them to a body. Hope you can help.
Hi Mike, have you tried pushing out the broken needle tip from the other end of the jet with a fine wire or something similar.Have you definitely got spark to the front cylinder! the reason I ask is I had a problem with the front cylinder not running but just checked the spark using the rear plug (easier access) turned out the live wire going to the front coil had come off, the spade connector was loose and had to pinch it with a pliers to make it stay on! -
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Hi Alan, the starting jet is not removable, unfortunately. It’s the long brass bit that sticks up from body (see pics above). I wonder what would happen if I chopped it in half, got the needle out, and epoxy glued it back together!!! I do have a spark!
Hi Mike, I do it’s not removable, what I thinking was if you could get a piece of wire in the hole where the jet enters the venturi and push the broken piece back up the jet. I don’t think chopping it in half would be a good idea.🤔
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Is there anything you can suggest I try with carbs in-situ Marcel?
Check Pilot Jet , it gets clogged very easily too.
Then while carbs and airbox are still on the bike, you can spray EASY START inside the airbox
Disconnect Rear Coil.
See if the engine actually sparks the front cylinder in to life and activate full choke , it should try to get it going. I expect if fuel comes out of the front carb, the plugs must spark it.
Or rear plug will be wet (as it was disconnected from HT coil)
But front will be DRY if its sparking and trying to fire
If its flooding, it will be very wet.
Looking at front and rear plugs will give us much better idea what to do next.
And also as per Alan above suggestion ^
The “starting Jet” really actually deals with starting mainly or fast choke system . It’s the Pilots to keep the bike idling.
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Thanks Marcel, I will try all this. However, I really just want to get the damn bike going. CAN you get me a front carb body, or even a twin carb set-up, and I would post you mine. The cost is not material now as I have already spent a lot of money, so I will pay whatever is necessary. Please ring me if you can.
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Hundreds of dollars to get a new carb you sure about that ?
Maybe email me and i’ll reply with some options in the used market too.
Single body (possibly)
Other twin carb set = Too much swearing to tune right, they have never liked other carbs besides what Korea provides them and as such they built the airboxes + intake pipes with the expectation of such carb.
Look at another recent topic on this site , someone has got a GV250 with a single carb and i was like wow! (The extremes the previous owner went to get it going!)
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Marcel – 😆 (see smily face!). I followed your advice to the letter, and after a while, spraying easy start (managed to find some in my local car spares place) in continuously, the front cyl caught but stopped (I had full choke). So choke off and a bit more spray and it ran continuously. Gave it a little bit of throttle slowly and it revved, so I stopped it, connected rear plug and it started, but only seemed to be running on the front cyl! I slowly opened the throttle, then when I got to 3000 revs, it took off! Back to idle and it was a bit hesitant again to rev, but again, at 3000 it took off. Kept it running for a bit, checked both pipes hot, then shut down. Waited a bit and then restarted – beautiful!
Now I must wait until tomorrow and see if it will start when cold. Before worrying about plug colour, should I wait until I’m able to do a road test? Assuming that tomorrow it starts again!
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It’s ALIVEEEEE!!!!!!! (Jim Carrey Voice)
Hey hey hey , get that girl going and you won’t need to spend hundreds of dollars on a carb! – If you must , clean it to the extremes and also use air compressor!
(I love air compressor after chemical baths , i mean i get to really blow every crevice , hole , slot , slit i can find in the carb, its a lot of passages lol)
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It didn’t start at first, with or without choke, but one squirt of EastStart again it was off! It started and ran with no choke 2nd time. So I’m going to re-assemble everything next week and hope for the best! I would really like to strip carbs again, but it is such a hassle that I’m going to risk it for a biscuit! Hopefully more next week and perhaps even a photo!
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