Depending on how and where you boat, the marine environment can be one of the best applications for a decently set up carb. For most of us, we boat at the same elevation and general temp range, this in itself negates two of the bigger drawbacks to carbs. For a sanely built marine, n/a app., I think carbs still make a lot of sense if you get them set up right to begin with.

I used to do injector development for Bosch. We garunteed to OEMs +- 3%. Densos with machined main bodies were the best at +-2%. The dynamic measurements were at a 2.5ms on time over a 10ms period.

Static flow rates are determined mostly by the orifice plate. Which could potentially erode over time. But boats get so few hours relative to cars.

The biggest issue I could see is that needle is harder than the seat and it usually wears a nice hard sealing surface for itself over time. This could also make the needle harder to lift off the seat and it would show up as higher variation in the dynamic flow readings.

I'm not surprised the Chinese ones are junk. There's so many places to go wrong in the manufacturing. Commenter above is correct, the strength of the magnetic circuit is important.

At Bosch our injectors were matched for flow at the dynamic rate during manufacturing by measuring flow as the needle spring force is set. We also experienced variation from machine to machine, making measuring anything less than +-1% impossible. We always tested statistically significant samples of 30, and used statistical analysis.

I'm surprised by how bad your findings are. I would suggest trying to control for the temperatures of your electrical components like drivers etc.

I'd suggest devising a test to determine your machines repeatability. Unfortunately this can be impossible to discern from a single parts test to test variability! At certain speeds I could watch an injector needle just spin around and around!

We test fuel systems mostly with viscor. It's essentially diesel fuel with an additive package to reduce flammability. I don't think it should be difficult to get.

I know some of OEM's say 7 % or less (some say 4 % or less as well in regards being in spec but alot of used injectors seem to be 10 % or even more off when flow testing. Also alot of times its not wise to mix new injectors with used injectors even from the exact same OEM. It might surprise you how much different the volume of flow comparing new vs old injectors can be.

Bosch has alot of equipment to test injectors plus all the R &D to do so - way more than anyone of our budgets can even think about.

Post #13 - I like the first sentence and totally agree.

With that said I sincerely hope the OP gets everything figured out. I have always been old school and like a carb/carbs on top of engines. It wasn't until recently I found myself researching a lot about good efi systems. Actually considering for 565 builds in the works. They have come a long ways over the years. The only thing that prevents me from doing so is when I read threads like this. I realize there are several good systems on the market working flawlessly however something is to be said about old school simplicity.

If you are worried about injectors have them checked out or buy from this company - one of the top rated injectors in the world - they teamed up with Bosch. Look at how they test injectors and so forth. I have sat in on anything they have for seminars in the past years. If you think you know alot about fuel injectors and fuel injection this place knows more about it than most ever could in a lifetime.

http://injectordynamics.com/company-overview/

That's pretty cool.

These other wanna be, 6 hand, know nothing purchasing from China toy factories ought to pay the ultimate price. When you have safety nets outside your factory cause so many are being worked to death 24/7 for food and housing I can imagine Quality is sacrificed. That's terrible what many are going through.

Thats the thing, i can tag the injectors that flow high or low, move them all over the machine, test 2 days later, a week later, they still flow low or high, pretty consistently. I might see a over achiever flow 10% high then maybe 1% one way or other, thats why i say in beginning my machine might vary 1% either way but if im seeing 10% thats big.

I recently became a dealer for racetronix who sells match flowed standard, bosch, siemans deka and a few other brands of injectors. The set of 63 lb i just bought matched within 2% either way on my machine , on different days, in different positions , was by far the best ones i tested.