Triumph t3 rocket starts but as soon as you twist the throttle it dies. If you get it to rev it backfires and tries to die. When you let off throttle it starts to run ok back to idle.

SOURCE: homelite leaf blover run with choke soon when chokeis off ,cant rev up and die

if he put fuel in it dump it out & put yours in it , if problem persist there are 2 screws on the carberator turn the 1 on the right or th bottom 1/4 turn to the left!

SOURCE: yamaha dt 200 won't rev off idle

You should measure the combustion ratio.Maybe piston rings failed.

SOURCE: Keihin CVK-D36 carbs on a 20 yr old ZZR 600

It sounds like your bike has been sitting in storage for an extended period of time (a year or more) - and the carburetors are plugged up. If this is the case, they will need to be completely disassembled and cleaned out.
If it hasn't been sitting (and the carbs aren't plugged up) then check that all of the normal tune-up items have been performed, especially valve adjustment, oil and filters, spark plugs, etc. If this fails to produce positive results, perform a compression check on the engine. Each cylinder must be able to produce at least 140 psi of compression in order to run and idle properly.

SOURCE: When I start my 10hp mercury outboard after

Be sure to run the recommended fuel mix. most modern 2 stroke outboard engines run on 100 to 1, some times the mix is on a decal inside the cowl.

Cheers, Timo.

SOURCE: i have a husky 455 rancher.never had a problem

When this has happened to me, it turned out to be a hole or crack in the fuel line. At the higher revs, more fuel is needed. The added "suction" for the higher demand pulls air into the line and the unit does not have enough fuel to run. Check for that first and also the fuel filter inside the tank. The filter might be clogged as well.

Keep us posted,
Dan

Testimonial: "got some very usefull stuff off ur reply, i did'nt know u could cx the fuel filter. Turns out my prob was actually a bad batch of fuel, but your reply gave me many options if it happens again in future. thanks for you time."