Motorcycle Repair: 1974 Yamaha TX500, yamaha tx500, speed jets

Question
I have a 1974 Yamaha with 10K original miles.  It has been in storage for a few years.  I recently pulled the carburetors, soaked all metal parts in solvent, cleaned screens, verified no orifices were blocked, etc.  I have done this one time before and it worked well.   
The engine starts and runs strong, however, it often starts on one cylinder and takes awhile for the second cylinder to work.  

The problem is that the engine will not idle for long.  It idles around 1500 rpm for a while, then begins to race, up to near 6000 rpm.  I can hit the kill switch and turn it on again after the rpms drop to 1000 or so.  However, the same thing happens over and over; the engine rpm continues to increase.

I have worked around carbureted engines for years and know that small engines will "race" when the fuel mixture is too lean.  Also, I know blocked high speed jets can cause similar problems.  

I would really appreciate any suggestions you can offer.

Regards, Tim

Answer
Hi Tim,
It does sound very lean!
I have to be certain from your experience you have the carbs assembled correctly. Since the problems exist from start-up it is most probably the primary circuit in the carbs that is sick. It may be the float levels are off; you'll need to verify they are correct and the bowls are filling with fuel. If the bowls aren't filling with fuel the jets and orifices can't do their jobs. Many carbs have a drain valve, if yours does you may consider using  about a foot of clear fuel line here to "see" the levels in the bowls. Push one end of the hose on the drain connection of the bowl securely, bend the other end around where the open end of the hose is up higher than the carb throat. Secure it as best possible and do the same with the other carb. Now open the drain valves, the hoses should fill with fuel to the level in the bowls. You will have to eyeball the level here, normally it's near the top of the bowl, within 2-3 mm. If you have a problem with the float/fuel delivery it should be visible here. If the bowls aren't full or are filling too slowly this may be the cause of your problem.
Best regards,
Terry.