Hello gentleman,
I need your help to troubleshoot my 2008 Hyosung GV650 ( carburetor model ). Motorcycle has 1,500 miles. Currently the motorcycle is not running.
I bought the motorcycle a year ago ( off Craigslist), garage kept, looking good and running okay..
The day I bought it, I rode it for the whole day, logging like 200 miles, without issues.
Then I parked it for 6 months in a friend’s shop ( decided to travel).
After 6 months the motorcycle would start and run but turn itself off after a few seconds or minutes, or when I would rev it, or when the choke would be pulled, or when I would drop it into the 1st gear…sometimes it would make it around the block, but not more then that.
I figured that I have a carburetor problem.
I changed the oil and filter and it run a little better, but then the starter solenoid broke, and had it replaced…since then the motorcycle started to act a little weird.
It would start ( when it wanted to ), so it was time to clean the carbs.
I stripped the carbs and soaked it in muriatic acid, sprayed carb cleaner, and compressed air.
The membranes are fine.
The carbs looked okay, not too dirty, but to my surprise the carbs were setup ( by the previous owner) to run with the air/fuel screw turned in all the way.
After I cleaned the carbs, adjust the float height and the air/fuel screw the bike still would not start/run without pulling the choke or twisting the gas.
* One day I filled the carbs and lines with Seafoam and gas and let it stay for a couple of days and to my surprise, the bike would start and run LIKE NEW, I could not believe it ! My excitement faded away 1 hour later and 5 miles down the road…the bike would act up again getting hard to start and/or stay running.. This is what drives me crazy.. the bike would not run good, then use Seafoam and the bike would run good for a short time and then acting up again, all this without touching the carbs or any other component. The bike was running perfect with and without the air box/filter..
I kept on playing with the carbs and now it would not start at all regardless what I do.
I will not start even if I spray starting fluid into the carbs.
Bought a used carb from a gt650 and still no luck ( I had to clean and adjust the “new carb”).
Compression is at 200 psi both cylinders.
I have good spark ( I would say).
I took the coils from a 2009 gv650 EFI – a friend’s bike ( I know they are different..) but same result.
I installed new spark plugs. The old sparks were black coated in carbon ( the engine was running very rich, black smoke when revved and backfire )
Bike is stock , factory air filter and exhaust.
Valves have carbon deposit.
* When the bike was running the rear cylinder was running 10 degrees hotter then the front cylinder.
Also I checked for vacuums leaks ( spraying starting fluid around the engine/ carbs / hoses with the engine running, and I couldn’t find any ..

Could I have a timing / ignition misalignment ?
I am a little scared to open that engine, but I guess that is what is next..
I am running out of ideas..

Any advice would help.
Thank you