Why we cannot guarantee fitment with GX390/Clone engines! (Chinese Inconsistency Explained)

Since 2012, our mission has been to make it easier for gas golf cart owners, to increase the speed and power of their golf carts.
The single biggest problem we have run into over the years is inconsistencies in Chinese "clone" engines of the GX390 platform...No other variable has caused my team and myself soo much stress and frustration. 

Background:
These days, most products you buy are made overseas including the vast majority of engines. While this keeps costs down, you have to consider the downside of outsourcing manufacturing to another country.
The companies that you buy from stateside (Harbor Freight, Home Depot, etc) are simply importers/distributors that have no control of the manufacturing process of the products that they resell. Likewise, they have no direct control of the quality and have to rely on the manufacturers own internal quality control mechanisms (if any).
The manufacturers in China have hundreds of customers and thousands of underpaid employees. Many of these factories house their workers in poor conditions and also provide for their basic needs in order to keep their labor costs as low as possible. This leads to a lack of genuine care for the well-being of the company or end-user as a whole.
Because the factory does not have to deal with the end users of their products directly, their main focus is not on the longevity of their products, but maximizing profits for the owner of the business.

Why consistency is virtually impossible:
These factories never make 100% of the engine components in house, in fact, most parts of the engine are outsourced to other companies. (ex: they get pistons from the piston factory, valves from the valve factory, etc.)
Its in the best interest of the engine factory to pick the lowest priced vendors for each individual component so they can maximize profits. Now imagine if there are 6 different crankshaft companies and they are all competing for the same business...eventually there's going to be 6 slightly different versions of crankshafts that end up in the engines that are sold by one engine factory.
You can now see how little things like auxiliary hole depths, placements, and casting quality can end up all over the place...even if the engine "looks right", it may not be right.

Supply Chain Challenges:
Companies like Harbor Freight sell such a high volume of engines, that they cannot always rely on one single vendor and must use multiple vendors to keep them adequately stocked with product. Take the info you read above and increase the complexity exponentially with every vendor they add to try to keep up with demand.

Conclusion:
Even if we tried, there's no way we would be able to make a universal product that fits every single brand, version, revision of the GX390 "Clone" engines. There are over 500 engine factories (that we know of) in China and over the years we have seen constant inconsistencies with ALL brands of engines.
Most of our products are based off of Harbor Freights Predator engines and since 2018, there have been 2 major changes to the 420cc engines alone that rendered our exhaust headers incompatible.
One would wonder why we don't update them to fit and that is because if we do so...our product then wont fit the 460s and Honda GX390s that it was originally designed for.

Solution:
1. Buy a genuine Honda GX390 engine as they have maintained consistency for over 30 years and document the changes to their product very well.
2. Deal with the inconsistencies and work around them. Accept that you are putting a well-engineering product onto a cheap Chinese engine and you might have some issues.