Motorcycle Repair: 74 Yamaha tx500 - carb issue, yamaha tx500, throttle cables

Question
falcon,
first off i appreciate you taking the time to read some email from a stranger.  

i just got a near mint tx500 off of a guy for a real good price (basically a steal) but it hadnt been run for about three years.  i cleaned the gas tank, new plugs, battery, points, oil, and so on and got it moving.  BUT here lies the problem. haha

when i start it, the rpms get up and get to normal range...but then keep going. ive let it get to 6000 before i cut it off and sometimes when running, it will calm down for a second or two and then just start climbing again. once, it actually hung around its normal idle for about ten seconds and then...up again.   

if i back off the throttle set screw it will not rpm/idle down until it cuts out completely.  kind of an "all or nothing" thing.  none of the throttle cables are caught at all and the linkage/interior carb vents dont even move at all when this happens.  i dont really understand how the bike can rpm up without the throttle opening a larger airflow through the carb.  

i can ride it like this (barely) but when i pull in the clutch and take the load off of the engine the rpms start revving up again. i dont know how high that thing would really go...

could this a timing issue, independent of the carb?  im in the early stages of motorcycle repair/maintenance but interested in learning.

thanks a lot for taking the time... i hope this an easy one that i can chalk up as a beginner mistake.

gerst

Answer
Hi Gerst.
 The problem is not in the timing.  I believe that the problem is completely in the carbs.  A combination between the idle speed adjustment as well as something in the carbs sticking open or not closing all the way.

See if the carbs are all moving through the entire motion range and check the choke for correct movement as well.

Start there and let me know what you find.

Good luck.
FALCON