Lt1000 20hp. briggs electrics on carb it will run when you pour i

This sounds like a problem with the suction. If the air filter is clean then it will need new carb gaskets. There may also be an issue with the pressure being created by the engine.

under the carb, bowl is there an electric fuel shut off. sometimes they stick shut or hardly open so sounds like it is open enough to fill bowl with gas but not enough to keep it running

the float is open and letting gas get into carb need new float and valve

needs to have carb cleaned out. most likely the main jet in the carb is plugged. symptoms include only running on choke and dies when choke is turned to run. or if you only have a primer bulb, it will only run for only a few seconds every time it is primed. if you are qualified to work on the carb, dont forget to start with fresh gas and possibly new fuel line and filter. R

blow air back threw the line towards the tank you have something clogging it or you forgot to turn the fuel on

my vtwin starts but runs fast and slow like it is running out of gas whatcauses this

I took the carb apart and found that it needed rebuilt, I installed the new carb and fuel pump kit and it runs great again.

You need to take the fuel system down, to see whats is going on. The fuel line from the tank to the carb is it clear? will gas pour out if disconnected? If yes now you will have to take the carb off and take it a part to clean it. That should fixit.

If you're using ethanol-blended fuel, the ethanol will eat away at the neoprene parts inside the Briggs carb.Going to need a carb rebuild.
Don't run your engine until it's fixed or you could damage it as gas will pour into the crankcase, causing the oil to thin and lose its lubricating ability.

CARB CLEANER FOR CARS WILL WORK JUST FINE,BUT YOU MIGHT HAVE TRASH IN THE BOWL.IF SO YOU WILL HAVE TO TKE THE CARB APART