Fix what you have , it works well when clean and adjusted properly.
Maybe we could help if you tell us your problem

Yes, tell us your problem. There may be a simple cost effective solution. An EFI retrofit, if it were available, would not be one.

p50 carb upgrade

Problem always has been (since new) slow/hard to start. Cleaned often. Still won't start if high idle lever is moved up at all...dealer says just keep cranking until it starts and do it until it keeps running and leave the lever alone. It starts/dies about a dozen times til it stays on. Once warm it's fine. For years now I've given up and use starting fluid to get her goin and keep her running til warmed up a little. Since there's no kind of choke , it's running lean when cold. (or rich when warm if I make it right when cold)

your engine if fixed correctly, will start and idle WITHOUT the use of the warm up throttle lever.
its designed that way.
in fact once fixed correctly use of the warm up lever will make it hard to start.
use the Yamaha dealer locator function.
find a dealership with a master tech.
leave the current monkeys.

When an engine is cold there is insufficient fuel for the amount of air that enters the motor. So, a choke or fuel enrichment device provides an extra amount of fuel to be added to facilitate the start and warm up process.

If you raise the idle lever you allow more air into the engine at the exact time that there is already too much air.

Your motor has a prime start device on the bottom carburetor to provide extra fuel when the motor is cold. There is a test you can do to measure if the pin length of the device is set correctly. Has that test been done?

There is also a trick whereby the prime start device can be modified so that it provides a bit more fuel when cold, or allows it to provide extra fuel for a longer period of time while the motor warms up. Has anyone mentioned this to you.

Does your motor have a red lever that can be used to override the automatic function? If someone has turned this lever to the OFF position then the prime start will not work. See illustration below.

Finally, have the carburetors been thoroughly cleaned? By this I mean have they been ultrasonically cleaned in a hot carburetor cleaning solution with all passageways having been verified as open?

As a last resort, you can discuss with your mechanic the possibility of changing the idle jet to one of a larger size. This can do wonders in some motors.