When I put it in gear the engine stops - 2003 Yamaha V Star 1100 Classic

sounds like a vacuum leak

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Replace the Torque Converter Switch

Your trans is working like a standard shift,
when you forget to put the clutch in at a stop

i just had same problem. It was the crank sensor. Cost $95 for part

check engine and gear box mountings

this can be a problem with the clutch\ side stand switches. Use a multi meter to check the switches work

Well, there is only one thing I can think of in your situation. Your pressure plates just simply are not creating enough pressure to allow the gears to engage. Either you have a defective clutch and it needs to be replaced, or possibly just needs a ton of adjustment. When you put it in 1st gear while engine is off, then start it and take off that works b/c there is enough pressure to keep the gears from starting to move when not already moving. However when they are already moving, there is just not enough pressure to stop them from turning, not even long enough to shift. Have you tried forcing it into 2,3, or 4 while driving without the clutch? As long as you achieve the correct RPM's your transmission should be able to do so.

Check gearbox oil

most probably the throttle body is whats causing it to stop. first try removing it and clean it thoroughly with any carburetor and choke cleaner if that didn't solve the problem have the engine diagnosed for any faults or errors

Yes the clutch is the problem, master and slave should always be replaced together.