19 horse Briggs & Stratton will only run with choke half on

I would replace the fuel lines with quality hose such as Gates brand, and make sure the tank is spotless especially the exit nipple (debris gets caught in them). Along with that verify the intake gasket seals are good and not reused. This is not a governor problem; it is a fuel/air issue.
 
Sounds like the engine is sucking too much air or starving for fuel. You changed the carb so it's not that. Check fuel filter and gas line and tank (trash in tank or not vented). I would also look for a loose part (maybe the manifold) or a crack (in the manifold).
 
I have one of those engines on my Craftsman rider, it was hunting real bad, turned out to be the anti-back fire valve, put a plug in it's place, runs good now (all summer)
Thanks,
Doug Lee
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Hint: (from experience with your issues with those type engines)
Those engines have a plastic intake manifold (that will warp leak air
AND
The o ring manifold gasket at the engine can be replaced with a flat gasket
AND
The Nikki CLONE carb is also a source of problems.
The really good carb is the Walbro LMT and can be found on flea bay every once in awhile.
Also good idea to always check the static governor adjust after replacing or working on a carb.

A bad measley spark plug can make you feel weak upstairs. (after you have spent several hours and dollars replacing other things)

Read post #11 couple times.
 
Run it with choke 1/2 on and run water over intake mount and carb mount to verify no leaks. If its leaking engine rpm will change. I use oil to check as its thicker and won't get sucked in as easily.
 
Changed carbs adjusted valves still the same thing hunts real bad only runs with choke half on. Changed carb head gasket and lapped the babes still hunts an dies without choke on
Had a couple motors did the same. one the main jet had dirt in it, the other look for air leaks around the carb.
 
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