GT650 Comet EFI 2010; Stalling issue at idle after revving
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Bought my first bike not that long ago and the bike started having problems a few weeks ago, it would randomly stall when taking off and then after stalling it would have great difficulty starting again. It started with a sudden surge drop in power for a few seconds then gained power again as I was a few meters from my driveway and then the next day it stalled on the main road and kept stalling when putting it in gear. I ended taking it to a mechanic around perth who had a diagnostic tool. They had a look at it and replaced the spark plugs, fixed a couple serrated wires at the back, did an oil change, adjusted the throttle cable and reset the ecu. I bought it back home and ended up installing a new after market fuel pump after still having trouble with it starting. That seemed to fix the problem and it idles perfectly now at a cold startup. But now after taking off and revving it a bit, it stalls basically whenever I let go of the throttle at a stop or holding the clutch to downshift. Even at idle I can rev it up a bit at a cold start and it will idle back down fine without stalling but as soon as it runs for a bit it stalls when I let go of the throttle. I had a look at the TPS (Throttle positioning sensor) and it read 3 and half volts or something when it was cold and it read 1.31v right after running it hot.
Here’s a couple videos of it running and stalling
Just wondering if anybody has any idea as to what the problem could be?
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Hi
I do not have a 650 but went off and did some reading on it and this problem. It seems that the ECU was changed in 2009/10 and the 2010 can have the issue you describe. I have read of ECUs being returned and reprogrammed but with no help to the bikes stalling issue. People also seem to of replaced rectifiers etc to no effect. My gut would say a sensor failing making ECU compensate.
I noticed that you have no FI light come on.
A couple of people solved it by replacing the throttle sensor.
Hopefully Marcel sees this and has an answer for you, he really does seem to have a vast knowledge of Hyosung’s little hickups.
Here is a Netrider forum post that looks at your issue, same bike same year; https://netrider.net.au/threads/2010-hyosung-gt650-misfire-and-stalling-when-hot.111646/#p-body-main (I imagine that you have already read it).
Good luck and keep us informed. If I find any actual useful info I will post it.
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Thanks for the advice. Replacing the tps is definitely an option, I’m also waiting on some injector coils and a new air filter delivered. Somebody mentioned on the form that heat from the exhaust could be allowing heat on a sensor, one thing to note is that I did drop the bike (which annoyed me heaps) and this problem happened not too long after that and there is a little bit of black soot leaving in the mufflers gasket. Sometimes when I start it, I notice that there is a lot of smoke coming from the exhaust in different places.
This is with the engine off, it smokes in three different places not including the exhaust outletI wouldn’t of thought an open exhaust could cause stalling issues, but I’ll take a better look in the morning and see if there are any sensors getting too much heat
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Sorry meant to say the tps voltage does not look right everyone I have seen the voltage is stable, the fact it’s dropping when hot says something is breaking down to me, the exhaust leaks you just need a new manifold gasket that’s the front sorted the rest just some good exhaust sealent will sort that.
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Sorry to keep adding but I’m not sure where the throttle was when you took the voltage reading if it varied in the same position then the tps has got to be the problem the fueling would be all over the place.
Both of the tps readings had the throttle closed, just at different temperatures, it read about 3.5v when it was cold, started it up again and measured the voltage with the engine running and after stopping it when it’s hot and it read 1.31v both instances (When it was on and when it was turned off and hot) with the throttle closed.
Also had a look at the electrical leads and connections around the bike, most of them were saturated in oil so I gave them the best clean out I could and I replaced both of the ignition coils. Bike idles higher (Probably because it was colder) , exhaust pops a bit and it still stalls when I let go of the throttle when it’s hot.
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I measured the TPS again.
Turned the bike on, with ignition left off, tps measured:
3.64 With throttle off
0.49 With throttle fully on (From the handle bar)Turned the bike on and let it idle for a bit, tps measured while on:
3.61 With throttle offTurned the bike off after it reached 3 bars of heat, tps measured:
3.61 With throttle off
0.49 With throttle fully onThis time I didn’t let it stall out after revving it (TPS read 1.31v right after I stalled it last time). I did notice, however; that it smoked heaps (Blackish smoke) from underneath the engine where it meets the exhaust after it reached 3 bars on the temperature gauge.
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That tps is definitely wrong from what I can figure out, there’s 2 types of tps a 2 bolt & 1 bolt both should read 1.v something at idle & 4.v something at full, the black smoke is over fueling with a voltage at 3.v something the injection time will be increased but the throttle is closed = flood out = stall, it could I hope not be an ecu fault. Its hard trying to diagnose something when I can’t physically get hold of it but I hope this might help.
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So I took the fuel tank off again and after measuring the tps again, it came back at (1.34v throttle off & 0.18v throttle on) (Which is weird because it was cold again and I never modified anything since measuring it at 3.64v before) . I took off the tps lead, ripped off the electrical wiring for the sensor and played around with different leads with the throttle on and off. I swapped out the black/orange lead with the green/red lead and reversed the connections and the tps read 0.49v with the throttle off and 1.65v with the throttle on.
I tried messing around with the tps and adjusting it but I couldn’t get it past 0.71v with the throttle off.
Put everything back together and tried starting it up anyway, it wouldn’t fire up for a while but it did go occasionally but wouldn’t stay on longer than a second.
I think I might to see if I can find another sensor somewhere locally or wait for one online and try again with a new one.
The tps is a single bolt as well.
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Hi,
Just joined and have been reading through this topic since I seem to be facing a similar issue, for the second time.
I own a GT250 EFI 2013 and a few years ago I started facing stalling and misfiring issues roughly after about 15 minutes that the bike is on. I spent may hours trying to diagnose the problem including the replacement of ht cables and plugs, ECU change, and injector cleaning.
In the end the problem were the ignition coils. I started with replacing one which reduced the missing significantly but since I was still getting some misfiring I replaced the second one as well. There were no external signs that any of these were heating up and getting intermittent.
For the past 2 years I have had no further issues but lately it seems the problem is starting to rear its head again though not as significantly. I am assuming it is the coils again but I am somewhat disappointed if the coils fail again after such a short period. I don’t make heavy use of this bike since I prefer my scooter for city riding.
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Hi, Just joined and have been reading through this topic since I seem to be facing a similar issue, for the second time. I own a GT250 EFI 2013 and a few years ago I started facing stalling and misfiring issues roughly after about 15 minutes that the bike is on. I spent may hours trying to diagnose the problem including the replacement of ht cables and plugs, ECU change, and injector cleaning. In the end the problem were the ignition coils. I started with replacing one which reduced the missing significantly but since I was still getting some misfiring I replaced the second one as well. There were no external signs that any of these were heating up and getting intermittent. For the past 2 years I have had no further issues but lately it seems the problem is starting to rear its head again though not as significantly. I am assuming it is the coils again but I am somewhat disappointed if the coils fail again after such a short period. I don’t make heavy use of this bike since I prefer my scooter for city riding.
Maybe you could make a new topic about this ? and perharps include more information about the history of the bike etc and what you did in the past to fix anything etc , and any modifications done to it etc… Do this all in a new topic and trust me if i don’t reply , someone else will and also simon on this forum is a good 250 wizard himself , even helps to also upload any video about it (you can upload to your instagram or youtube and set video to public, then share link here, if it helps)
Welcome to the forum and hope maybe one of us will help you fix the bike
While you wait, take a look at the service manual that’s on this forum and try to trick your ECU to get any stored error codes.
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