Is that the Wags Engineering adapter? If so, I have used them and they work well.

Not to throw another wrench into the AFR but timing can play a role on AFR numbers. If your not "advance" enough it will read rich as its not burning all the fuel. This is why dyno tune is a key because you can see where HP starts dropping off with to much timing then set your AFR numbers from there.

You probably don't need an 850 carb. on a stock 502,, over carbed, and look at the spark plugs, if they are real black w/soot its too rich, if they are white its too lean, and look at the back of your boat after you run on the water, if it is black with smoke film that is the first sign it is rich, read the spark plugs until they look correct.

I'm super old skool! AFR doesn't care WHY it's lean or rich, it just says it is or it isn't. Unless the boat is set up for one, I don't know I'd spend a bunch to incorporate one. It's STILL a carb, and the setup today at 533ft.above will be a tick off from sea level. Carbs will be a touch fat some places, a touch lean others. It's the reality of carbs. (which I love by the way) You gotta find that little sweet spot.

Start FAT: fat engines live. Work your way back to a leaner setup. Changing cam on the acc.pump and secondary linkage, jetting, plug reading-- it's all kind of a lost art with EFI.
850cfm might be a little big, but it's doable. Just need to tweek on it alittle. Get it right and you'll never know it's not EFI if you don't lift the hatch.

a 750 would be much better, also with the tunability of some of the newer carbs(quickfuel I know) you can dial in damn good AFR's in just about all of the ranges, just did so on a blow thru which I was told would not happen...

Ill have to double check the model number, could be an 800, heck with my experience and knowledge it could be a friggen 250 lol, the seller said it was an 850 so this dumb ass assumed it is. when warm it starts like an efi, maybe faster, when its cold it wants a couple of pumps of throttle (no choke, plate removed) but some times Ill get a pop back through the carb (only when cold) smells rich at idle but due to thru prop exhaust I dont see any black. I'm going to follow the richness adjustment method with a vacuum gauge this weekend and have a look at the plugs. Ill take it from there. Thanks again for your input, I wish one of you were close!

If all else is good, and If you get a pop back thru the carb, when trying to accelerate (even a little) it means you did not warm up the engine enough.

Fuel puddles on cold intake manifolds, cyl head runners, and intake valves.

And that's the reason for chokes.....less air means extra fuel.

So...let it warm up more.

if it has popped ck power valve, they blow very easy even with the power valve protection they now use..

I also have been experiencing a pop through my one carb. I have Holley 850s on gen 6 454s primaries are 72s and the secondaries are 84s, 088 heads, Holley strip dominator intakes with thunder bolt ignition. After I push it on plane, if I run around 2800 rpm I get a pop through the carb, I have also heard a tick which could be pre ignition or detonation but it doesn't happen often usually it shoots trough the carb. If I run straight to cruising rpm (3600rpm) It seems fine. Plugs look good, doesn't appear to be lean, timing is 32 degrees. I'm running E-Top headers, smells fat at an idle, fires right up as the chokes are functional, no bung for o2 sensor. Still trying to find the problem.

Primary jets seem low. 750's-800's have prim jets in the 70's...not usually 850's.

Have you tuned this or just plunked the carb on ?