What do you mean when you say the aftermarket carbs typically have about a 75% failure rate?
I got that failure rate upside down. I get the Nikki's from Amazon prime and have about a 20% failure rate. (2 out of 10 that I can return for a full refund.
I usually just turn around and order another and get a go.
Usually about $15 for the single barrel type with free shipping.
What I've found that usually causes a good running carb to fail is long term storage from a machine not being used and or use of ethanol gas.
A Nikki carb that has been know to have ran good on a machine can usually be easily re-built right when it first starts running rough on a machine, but a new China clone that does not operate correctly when NEW is usually a waste of effort, especially when it can be returned for FREE.
Also no need in wasting money on more expensive carb just to test a used engine that might not be any good such as a oil burner.
But on another subject, on a new to me engine that I have never seen run that is missing lots of external parts I run a leak down test to get general idea if it's going to be a oil burner, head gasket leaking and if the valves are sealing, before I start spending any money to get a test run and then see a oil burner or worse.
Here is a link to a you tube video that gives some hints about working on a single barrel Nikki carb.
Another link to find carb kits and carb pieces at reasonably prices and shipping not inflated. (PLUS LOTS OF OTHER STUFF) They are a fast shipper to the lower 48.
Click on the menu bars at upper left corner and select for example Briggs and Stratton Carb (when you see a Nikki carb part number you have to search as a Briggs part number, NOT NIKKI PART NUMBERs)
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