My rc51 1000 starts fine, idles fine,but occasionally when switching gears it will stall, when i pull back on throttle between gears, thats when it stalls, but every time it starts right back up on the fly. mark

The first thing to try is putting a couple of fuel tanks of injector cleaner (properly mixed) through the injection system.

Also clean the IAC (idle air control)

Occasional low idle at stop/engine dies

Harley Davidson Forums https://www.hdforums.com > ... > Softail Models
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08 Softail Won't Idle, Dies Out, Difficulty Restarting

HDTimeLine https://www.hdtimeline.com > threads > 08-softail-wo...
Aug 24, 2014 - Several months ago the bike started to die out for no apparent reason. It would spit and sputter in 6th gear and then refuse to hold an idle.
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Possible torque converter clutch issue. Is the check engine light on? If so, have it scanned for transmission codes. If the torque converter clutch is locked up when it isn't supposed to be, the vehicle will stall. Another thing to check is for coking on the throttle plate. Remove the hose that goes from the air filter box to the throttle assembly and look inside the throttle bore to see if it is dirty/black. If so, use carb cleaner and a toothbrush to clean while holding throttle plate open and remove as much carbon deposits as possible. This can affect minimum idle airflow and also cause a stall

Idle air control ! Ford IAC Test stalling problems Ford GM Chrysler there all the same ! How does it idle out of gear , smooth or ruff !

check the throttle lines ,set idle just above stalling point if need be

Engine stalls or RPM fluctuates at idle up and down or dies near idle.

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve but always run a OBD2 fault code as well as the cleaning procedure. Buy a can of throttle valve cleaner (do not use carburetor spray cleaner!) from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control

I would suspect that the float is sticking. Checking will require removal of (in order): seat, tank, air filter box/backing plate, and finally, the float bowl at the bottom of the carb. Insure that the float is not flooded, and that the float needle is free of trash.

Clean the Idle air control valve (IAC), it's located by the throttle body so the best thing to do is give the throttle body a good cleaning with throttle body cleaner. Do not use carb cleaner, it's to corrosive for the gaskets used on the throttle body's. Just follow the instruction on the spray can and after your done putting everything back together. Turn the ignition key's to the run position for 10 seconds and then off for 10 seconds to reset the IAC. Start the engine and let idle for 1 min and go for a test drive. If that does not work, turn the ignition to the run position and pull the ecm(BATT) fuse out for 30 seconds and then place it back in start te engine. The engine may stall but let it, don't touch anything. Just start it again and let idle for 1 min then go for a test drive. The ECM is just relearning the sensors like the first time the jimmy was driven off the assembly line. Good luck and hope this helps. Keep me posted be glad to get your jimmy running 100%. 

You may have a problem with idle speed control motor or ETC as GM calles it. here is a photo and a price from rockauto.com.
STANDARD MOTOR PRODUCTS Part # SA4
Motor Assembly $110.99

this is cause because the ISC is busted or can not open enough to keep idle at 800 rpm.

ISC , idle speed controller

but....
the car has a TPS switch on the throttle body.
if it fails to close at idle the ecu will never attempt to set idle.

or
car could be flooding. (too much gas)

you did not say if motor is 8valve or 16v and they are quite different EFI systems.