You should check that your battery is properly charged, first of all. If it's even a little low, it can cause problems with starting.
If you check that and find it's OK, next you check the coils and ignition electronics. If the coils are shorted once they fully warm up, they could stop firing the plugs. Same for the rectifier and regulator, if equipped - once electronics get warm, funny things can start happening. They don't really have a "failure mode", so it's difficult to diagnose some things without properly testing them in person.
You can get a $2.50 spark tester tool from your local parts store, and run it inline with a spark plug to see if you're getting fire to the plugs. If you are, you may just need a carb cleaning. Even with only 100 miles, there's a good chance you got crud in the carb.
You can test if it's the carb by spraying a quick shot of Starting Fluid into the carb throat and cranking at full throttle. If it starts, even for a second, then the problem is in the carb.
The problem is that it is not getting fuel fromthe tank to the fuel line and then to the filter....must be something with the vacuum system that pumps the fuel???
I'm sorry, I just got the email that there was a comment here.
If fuel isn't flowing from the tank, the petcock is either plugged or the vacuum diaphragm isn't working correctly. If you have a vacuum pump (brake bleeder pump), hook it to the vacuum hose on the petcock and pull about 12 inches of vacuum. See if the fuel starts to flow that way. If it does not, the vacuum diaphragm in the petcock isnt' functioning correctly.
You can also try blowing shop air through the petcock's outlet to dislodge anything that might be in it, clogging the inlet. Don't blow 120 PSI through it, but 40-50 should be more than enough.
I'm fairly certain you can use a tire chuck on the fuel line nipple. The nipple should be long enough to open the tire chuck's valve.
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How new is the fuel filter? Did gas sit in it for a long time without being used? If so, maybe the carb is gummed up.
Also, I would remove the spark plug, hook it back up too the coil wire, lay the probe end of the plug on the head or 1/8" away from a steal/metal surface, then turn it over and observe the spark. Make sure it is a good strong bright spark otherwise change the plug and if needed, use a voltmeter on the coil and see how much voltage your getting.
Check to make sure the valve clearences are not too tight. If they start out too tight they will get tighter when they are hot and this could cause your trouble. Also make sure the carburator boots are tight on the carb and the cylinder head, any air leak here will cause a lean mixture and hard/no start condition.
Got to see if the motorcycle has gas going to the engine. Next time it stalls, take the spark plug out, and put a teaspoon of gas in to the cylinder, then replace the spark plug and see if it starts.
If it does, then the carburetor floats are likely not set right or the carburetor is plugged up. I'm assuming this is a 4 cycle engine and not a 2 cycle engine.
But, even so, if it's 2 cycle then the carb is getting stuck not allowing gas to flow.
Also, check the fuel filter.
Good luck on this repair. Happy riding.
Have you disassembled the carburetor to verify specs. on the float, or to see if there is a 'float' related problem?
Think of it like a lawnmower with a bad carburetor, there could be gunk in there.
right?
What did you check out electrically, the spark?
FUEL ISN'T GETTING TO THE CARB. IT IS NOT FLOWING FROM THE TANK. ELECTRICAL IS ALL GOOD, WIRING, FUSES, VOLTAGE, BATTERY AND YES, THERE IS SPARK. MUST BE SOMETHING WRONG WITH THE VACUUM FUEL SYSTEM??
I would agree that you have a fuel delivery problem, in this case. Are there any vacuum controlled valves that would block the flow of gas if the vacuum hose wasn't connected (like in a 1985 Honda Interceptor, for example).
Do you have a separate petcock for block fuel off?
'blocking' fuel rather than 'block' fuel.
If you determined that the tube connected to the tank is not allowing fuel to flow, then there is likely a blockage there.
But, you said you blew it out with compressed air.
Could it need to be primed?
What is the pathway of the gasoline from the tank?
I think that there could be a problem with the suction of the carb not being sufficient to pull fuel into the carburetor.
What kind of material is the fuel line made of, rubber, plastic, or metal on this motorcycle?
Does it flow down from the tank or does it take any twists and turns.
Can you describe this, please.
If you remove the line from the carburetor and the fuel doesn't just flow out well, then there could be sediment in the tank that is blocking something, depending on the design.
That's why I would like to know more about the routing of fuel from the tank to the carburetor and the flow of fuel inside the tank to the line. Please describe this.
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You have a bad contact in the electrical wiring: as the bike is running it heats up and the metal parts expand, breaking the circuit. When the bike cools down the contacts cool also so the metal parts contract making the contact. To test where the problem is all you have to do is to follow the circuit and test the voltage: at the generator, at the key switch, at the ignition module and is sparks are present at the sparkplugs.
The battery died because you either:
1 - forgot to turn off the key so when the iffy contact reactivated when the bike cooled it started again to consume from the battery .
2 - the iffy contact is at the generator and you have run the bike without the battery being recharged - to check for this just start the bike and check the voltage at the battery, a good generator will provide at least 14.4 volts.
I'll check this and get back to you. Thanks.
Just occurred to me: have you checked if the fuel filter, line and its sump from the tank are not clogged by dirt ?  Have you tested the pump by itself ?
In that case the fuel line is blocked - take it completely apart and remove the blockage or replace it.
I guess I am not explaining the problem correctly. The bike is not pumping the fuel. Modern bikes are not gravity fed! They are pumped or vacuum operated and mine is not pumping the fuel. The line is not blocked...the filter is fine...the gas is new and clean...no debris in tank.....something is not forcing the fuel thru the line to the filter.
Have you seen this line from my first comment?
  -  Have you tested the pump by itself ?  -Â
Did you followed it? As in have you removed the fuel vacuum pump and have you dismantled it to check for broken parts - the membrane most likely, and the valves?
If you don't know how it looks then here it is
http://www.hyosungsource.com/parts/gt250...
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I traced electrically and could not find the problem...any other suggestions?
My United Motors / Hyosung GT250R is giving me fits. I have checked all electrical and have changed the fuel ****, fuel filter, fuel dist. box and to no avail. It wont pump fuel from the tank consistently. It keeps stalling and when I pull the line from the filter....it barely trickles, or none at all...even with the motor started and/or turning over. I have emptied and blown out the tank...what am I missing???
fUEL IS NOT FLOWING FROM THE TANK.
I know exactly what it is... It's the fuel cap. In the fuel cap there is supposed to be a hole (at least one) that lets air in so there isn't a "suction" (vacuum) in the fuel tank from gas going out but no air coming in. In my Hyosung GT650r this hole was clogged with some sort of epoxy glue. It took a long time to figure this was the problem.... We ended up drilling a hole through the epoxy glue that clogged the hole and my bike has been fine ever since. So just take apart your gas tank cap, and look inside of it, if their is a hole, yet looks filled with glue or something THIS IS YOUR PROBLEM!!! Look for simple solutions first!!!!!!!
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