Bike will not idle

Many bikes have CV (constant velocity) carbs, and so have an enriching valve and not really a choke. The enricher just adds more fuel to the mixture.
The high idle could be a vacuum leak at the base of the carburetor. You can check for a leak with a can of carburetor cleaner.
Start the bike up and spray a short burst of the cleaner at the base of the carburetor if you get a change in RPM or if it stalls that's the problem.
Good Luck

Have you changed the fuel filter?

Has the bike been apart this sounds very like a timing issue?

When you first turn the key on, you should hear the fuel pump come on and build pressure - it will be a ticking noise. When the pressure is low the pump will run continuously, when the pressure comes up, the ticking will slow down and the pump will stop. The fuel pump is located behind the lowest cover on the left side of the bike - but you can hear it normally with the cover in place. If it's not working, check the fuse - it's in the same area as the pump if I recall correctly.

Also - check your fuel filter - it's under the seat behind the first plastic cover you'll see when you take the seat off.

If none of that works, you might want to drain the tank and pull the petcoc(k) and check the filters on it.

Scott

First check to make sure that both of the chokes are not sticking closed after the bike is warmed up. Also check if the throttle grip freeplay is comfortable (2--6 mm) when it sits in idling position. If both are fine then most probably the carburetor may need adjustment & should be left to a trained technician.

Lean mixtures burn very slowly, at times slowly enough to continue burning through the power and exhaust stroke, causing a backfire when the intake valve opens, and that flame gets a shot at the new mixture charge.

In normal operation, as the engine slows, the fuel delivery from the main circuit falls off, and the idle circuit is supposed to take over. If the idle circuit flows insufficiently, that becomes a transition to fuel starvation.

You can try pointing an unlit propane torch into the inlet air, and see if you can get closer to an idle while supplying a supplementary fuel source. You will need to do this in a way that gets propane to both carburetor inlets, maybe rigging a Y with vacuum hoses and electrical tape...

This started with work on the carburetors, so the fuel system would be the most suspect. That, and the fact that it will run at higher RPM would seem to rule out fuel delivery.

I was looking around at photos while developing this answer (needed to know whether this was a twin or a 4-cylinder), and one resource said the idle speed should be 1,200. I don't know if that's right, but maybe 1,000 RPM is too slow for this motor to keep it together. (I do doubt that, though.)

When I wrote that last sentence, I started to second guess myself, thinking "What if the fuel shutoff(s) is/are vacuum operated, and as the bike approaches idle there is insufficient vacuum to hold it/them open?" But the I rejected that, because there is even less vacuum at cranking speeds, yet the bike starts.

First check entire length of throttle cable for kinks, crimping or binding. (especially near steering head) Check function of twist grip, it must rotate smoothly and spring back when released. Ensure choke is turned off after initial warm-up. If no change, turn out idle screw fully,(owner's manual refers) start bike and keep throttle at idle speed and screw in idle screw till it engages.

You have an air leak at the manifold. Over-tightening can warp a manifold. The best thing to do here is to get a set of manifold gaskets and replace the old ones. Tighten the bolts evenly in three stages. Seven foot lbs of torque is proper.

take some wd 40 & spray around the carb boot while running to see if the idle drops for a few seconds. sounds like you have an intake side air leak causing a lean condition making the motor rev high.

well if the idle is surging(going from 1000 to 1500) you probably have air bubbles in your radiator. i had the same problem. just run your car and then fill it with anitfreeze and let it run without the cap on so all the airbubbles to get out.
and if it just stays at a constant 1500 you can just turn the idle down. a mechanic can do it pretty cheap