I can get it started and running on low throttle, but as soon as I gradually increase throttle, seems to die at one point.

clean the carburetro and check air filter, is the plug soaked in gas

Not getting enough fuel at higher engine speeds, if the carburetor is adjustable open the high speed jet about a 1/4 turn (screw on bottom of carb.).

If it does not have an adjustment screw then the jet is probably dirty and the carburetor needs to be cleaned out.

I'm getting to where I can take apart this carb in my sleep! The last time I opened it, there were black specks at the bottom of the bowl, maybe my fuel hose is disintegrating.

Ive read somewhere that fuel lines deteriorate and get clogged around 2-3 years???

What is the complete model and spec number off of your engine

The engine is TVS115-62101A (D). It is same as previous post of mine. It fixed up last time I disassembled/reassembled the carb, ran correct for a day, now has this problem.

Sounds like you might have an air leak, check the mounting gaskets at the intake manifold and make sure carburetor and manifold is good and tight.

I sprayed carb cleaner fluid all around the manifold and carb while it was running, it does run at low speed, and no luck. Real shame because the unit is in nice shape, I salvaged it from trash pickup last year. I'm sure its something minor, but I'm tired of smelling like gasoline. May very well get a Toro.

I would double check the O-Rings you replaced and make sure they are still alright and that they did not swell up or something.

When you replaced them, did you remove the nozzle and replace the one on top?

I got my other rider working, seems the ignition switch is going bad, second time in 5 years, so I can continue to work on this TVS115. The o-rings were installed correctly, yes you know that carb well, as the upper ring has to be pried out and I did leave it in accidently at first but noticed the jet was not at the proper height.

I had skipped the carb kit replacement because things looked on the up and up, but I'm now going to spring for it and a new jet (the old one cracked but held together) and replace all gaskets as well to see what happens.

Is the symptom I'm describing, starts and runs on low speed, but dies on high, most definitely a carb/manifold issue and not something else like the governor or something internal that might end up being alot of work? I also read the choke shaft might wear and be leaky, is this something that can be fixed or do you have to replace the carb?

It sounds like a carburetor problem to me and not a governor problem. There is no choke shaft on this carburetor, but you could have some wear on the throttle shaft, I don't think that is your problem as a worn throttle shaft is much more evident at idle speeds then when you throttle the engine. It sounds like you are just not getting enough fuel to run at the higher engine speed.

Good Luck

Ordered carb kit, will report back. Thanks for the help so far.