Hyosung GT250R wont start

Sounds like the gas tank may have some crud in the bottom that is prevent the fuel from flowing through the petcock.. OR the petcock itself is stopped up. Make sure the petcock is not stopped up first.. then make sure the tank is clean. My personal ATV went through this very thing...the TANK and the PETCOCK were stopped up.
You are going to have to remove the gas tank to do this,
BE CAREFUL!!!!

When you chaged the air filter & sprayed Gumout carb cleaner, you got rid of a little gunk in the
air intake, but when you added the fuel injector cleaner (its the same stuff as carburator cleaner) to the fuel tank, you "cleaned out" ALL the ****/gunk/buildup/dirt in the fuel system which has built up since 1991 and sent it straight to the fuel filter, which is now clogged. The reason that the car tries to start, but fails, is that it'll successfully burn up any fuel that gets past the clogged fuel filter, but the engine consumes that small amount of gasoline quickly, then dies.
Your solution: change the fuel filter.
The fuel filter is located:
Under vehicle, driver side, below seating area, near fuel tank, mounted on frame rail in fuel line

clean the carbs

My guess woud be that you either have not got the timing set correctly or something to do with the intake/ carb.

Since you say you replaced the advance weights, this tells me that you removed the breaker plate. I hope that you replaced the entire mechanical advance unit unstead of just the weights. The problem is that the pivot pin wears and replacing the weights does not replace these pins. I always use the needle bearing equipped units.

Now, to check the timing, connect a timing light to the front cylinder and start the engine. Remove the timing plug from the left side of the engine and shine the light in the hole. Bring the engine up to about 2500 RPM. You should see a "dot" in the middle of the hole. If not, you'll have to move the breaker plate to change the timing.

Intake and carb. I've seen brand new intake clamps with new "rubber bands" leak. I always pressure test them. To do this, you must make a plate that replaces the carb and bolts on to the intake. In the middle of this plate, there should be a hose nipple. Rotate the engine until both intake valves are closed and apply about 5 PSI pressure to the intake. Spray soapy water on the intake and clamps to find the leaks. Once the leaks have been stopped, work on the carb.

If you're using the original Keihen carb, you'll probably find that the slow speed jet or the idle port is plugged up. I'd disassemble the carb and soak it in carb cleaner. Make sure all the air and fuel passageways are clear. If the idle mixture adjusting screw is frozen up, trash the carb and get another one.

Good Luck
Steve

Try cleaning the IAC valve locate near the air cleaner intake hole . Remove the aircleaner duct work. And when the car does start. Run engine at 1200 rpms or so. Spray carb cleaner inside the hole to the sides of the walls. you can see 2 small holes to the side of the walls. That is the IAC. Turn engine off ,let the cleaner soak in. Then restart the engine and spray some more. when I say spray , I mean a good 10 seconds of spraying right at the little holes . See if your car starts running better. if this does not work, replace the IAC it is on the outside of the fuel intake . You can also try the MAF sensor. Mass Airflow Sensor located on the big pipe on the air cleaning system.

Most likely the carburetor jet is still clogged after sitting for years with fuel in it. Putting injector/carb cleaner in the fuel tank may help, but if not, the jet needs to be soaked some more -- or replaced.

Follow mixing proportions on the label for injector cleaner.

sounds like the rings are fried and needs a new piston and rings.. for an 80 there about 110 bucks for the whole kit

Hi and welcome to FixYa,

Initially, if there is spark on the plug of the front cylinder, then it would be a fuel issue. Pls try:

• Rig a fuel bottle to replace the fuel tank;
• Remove the airbox assembly to expose the carb;
• Start/run the bike, spray carb cleaner on the open carb;
• note the RPM or sound of engine. Determine if front cylinder will fire even erratically. You could also try the exhaust pipe if it warms up (pls be careful might be overly hot);
• rev the bike then cover the carb mouth of the front cylinder with the palm of your hand;
• there should be a strong suction indicating that vacuum is created when on the intake stroke and intake valves are opening;
• the palm of your hand should be wet with fuel, if not carb issue;
• might require a rebuilt.

Good luck and Thank you for using FixYa. Happy New Year.