Forums 🚥 PiT STOP 🔧 Hyosung Technical Help GT650 EFI leaning out
- This topic has 20 replies, 4 voices, and was last updated 2 years ago by Jason.
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Aug 16, 2022 at 9:42 PM #8361
Hi all,
I have just bought a GT650 Comet EFI. It will idle fine but when I rev it it’s like it will only run on one cylinder and leans right out.
Can anybody point me in the right direction to start looking?
Thanks
Jason
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Aug 16, 2022 at 9:57 PM #8362
Check for any vacuum leaks also clean & check all the sensor connections
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Aug 16, 2022 at 10:01 PM #8363
sorry forgot to say make sure the plug caps are on properly you will be surprised how often they are not.
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Aug 17, 2022 at 2:08 AM #8367
When you say plug caps do you mean the spark plugs? I will start checking all the sensors tonight. Thank you for the suggestions.
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Aug 18, 2022 at 6:08 PM #8370
He also means the “black tubes” that actually connect to the spark plugs deep inside the engine but yes look for;
– Loose HT wires trying to escape the coil
– or Loose HT wire trying to escape the black tube (plug cap as it’s known as)
– Spark plug is tight in engine and is on the correct torque (max 15ft lbs on torque wench, engine is aluminium, so threads can still strip due to overtightness)Also grab a copy of fresh CR8E plugs (OEM) and use that forever, do not worry about getting “cold” type plugs etc, or adjusting the gaps of the spark plugs. There is other ways to help the bike stay a tiny bit cooler on blazing summer heat.
// Meditation doesn't mean you have to sit still....
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Aug 19, 2022 at 2:17 AM #8389
All great suggestions thank you.
I Have two EFI’s and a Carby 650. Both EFI’s exhibit similar issues, both have had rusty tanks which I have now neutralized and sealed. So I have pulled the injectors and sent them for a clean as well.
I will start on the rest of the checks this weekend.
Cheers
Jason
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Aug 19, 2022 at 10:47 AM #8391
You have added something to the mix there is every chance that the fuel pump seals have been damaged due to the moisture.
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Sep 1, 2022 at 4:02 AM #8488
So just an update….
I pulled the tank off and bike apart. I had the injectors cleaned.
One of the injectors was flowing badly. When pulled apart they had a lot of rust build up inside the feed caps.
A hose to the MAP sensor had a split at the top.
I have it back together and it no longer wants to lean out but when riding it feels like it can’t get enough fuel. Im suspecting that the fuel pump has had it so I have another on the way.
I will update when its fitted to see if this solves the issue.
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Sep 2, 2022 at 3:43 PM #8494
You got this! Keep us posted, well done on the diagnosis so far
// Meditation doesn't mean you have to sit still....
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Sep 3, 2022 at 1:14 AM #8495
Ok Fuel pump replaced with a new unit, I went with an uprated Kenso unit over the stock.
Changes in the bike now:
-Idle is now higher
-It no longer is leaning out
-Power appears to be there throughout the rev range.
New issue which I didnt notice before is i have backfiring out the exhaust and the odd miss. I suspect that this is plug related so ne CR8E plugs are on their way. I have also noticed that the coils aren’t earthed to the frame very well so I will clean up the rust and getter a better earth happening.
The timing is supposed to be set at 5 deg TDC how do I measure this on a bike?
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Sep 6, 2022 at 4:16 AM #8535
Last update for this thread I think.
Yesterday I replaced the plugs checked the leads and coil packs.
The plugs were average so replaced with new NGK CR8E
Leads looked ok.
The coils and where they mounted to the frame were fairly rusty so I cleaned them all off and re-attached.
The bike now has no hesitation and appears to go through the rev range happily.
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Sep 6, 2022 at 6:40 AM #8536
Great news
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Sep 11, 2022 at 7:17 AM #8566
So I was out riding the other night and only just made it home as it felt like i was riding on one cylinder.
I had not much spark on the rear cylinder so replaced the coil and it was a little better.
Checked the TPS and found that the measurements were way out so adjusted to put it back.
Went for a ride and it lacked pull when I throttled like it couldnt get enough fuel and when i pulled up at lights it would stall.
I fiddled with the TPS to get it to idle but now has no go above about 5k RPM.
Anyone have any suggestions?
Oh and no F1 light.
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Sep 11, 2022 at 8:15 AM #8567
Do you have any way to check; fuel-pressure? (regulator & fuel-filter) , Temp-sensor? , O2/lambda-sensor(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): GT250R-efi
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Sep 11, 2022 at 9:44 PM #8576
The only means I have to check the electrics is with a multimeter.
Just to digress a little, the manual only shows a two bolt TPS and not a 1 bolt. The pins appear to be upside down on the actual bike compared to the manual.
The fuel pump was replaced with a new unit.
https://www.ebay.com.au/itm/164748784383
The temperature has 3 bars on the dash. Before replacing the coil the rear cylinder felt noticeably cooler than the front.
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Sep 12, 2022 at 4:42 PM #8580
650Fi -(2009-) sm:
https://mega.nz/file/vcs1XDyI#NJuh8MykclBv4gAMsVozb-OIPRWDPSCP3tpwPqGg0BI
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): GT250R-efi
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Sep 13, 2022 at 1:41 AM #8604
Thank you
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Sep 19, 2022 at 5:45 AM #8652
Last update on this bike for a while.
I still had trouble with the bike running. Most parameters seemed to be in check.
I managed to borrow a compression tester and got the following results:
Front cylinder = 150psi
Rear cylinder = 90psi.
There is no way I will ever get tis bike to run properly with those readings. I believe 1 of two things has happened:
- Because of the blocked injector it has leaned out that cylinder so much it has annealed the rings.
- The timing gear has slipped a tooth.
Only way to find out for sure is to start pulling the engine apart.
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Sep 19, 2022 at 8:26 AM #8653
Could be something as simple as over tight clearance or a valve which wouldn’t be to much of an issue just a bit of mucking about.
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Sep 19, 2022 at 8:18 PM #8654
Was the compression also tested when engine was hot warm & full throttle with both plugs out ?
// Meditation doesn't mean you have to sit still....
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Sep 20, 2022 at 5:05 AM #8656
The engine was warm when I did it but not at operating temps. The last owner complained of it being down on power as well.
The other possibility is that it has slipped a tooth on the timing gear. When I get a chance I will pull the rocker cover off and start digging.
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