So I'm trying to tune carbs teague marine told me to start like this .I have a 502 stock,525 efi cam,420 mega,aluminum heads 330,chiller,2 750 Holley's, cmi headers,start with 80s and 86s and 10.5 power valves. I'm at 4000 ft.

your carbs are borderline on size and will restrict some power.imo you need to invest in a quality afr gauge to get close and then read plugs.it is the fastest and safest way to tune the engine.at your elevation the teague recomendation sounds like a good starting point.

I have to agree with Mike. With 454's that's a set up I'd use and have with the 420 mb minus chiller. No doubt you can make them work however I just think your sacrificing power and perhaps lean. 850's??? Are the carbs boost referenced? Rule of thumb is if you need to go up or down more than 4 to 5 jet sizes from stock - you have the wrong carb. I guess you'll see where you need to be with PV after seeing where your at with boost/vacuum gauge. Seems a bit large but who knows you'll know right away. Carb size with your set up is crucial. You can throw fuel at it or take away all day but without the right size ho's/bores you can be chasing issues for a while.

These going on dyno? If not you you using o2 sensor/afr or egt gauge?

It's possible your altitude will change things up for sure so maybe make a call to b&m or Teague. Potentially a 5 minute ph call may save you some time in the long run.

Where can I bung to put 02 sensor I have lightning headers

I just got a nice stainless set off Ebay and they have external hex plugs rather then the internal allen head.

without a wideband 02 like playing russian rulet

Holley's HP 750 supercharger carb, came with 76 Primary, 87 secondary, with a 10.5 PV. Boost referencing is not mandatory.

I have 420 mega blowers on my 468's with 850 holleys, and superchillers. While I do not know what the air intake temps were prior to adding the chillers, I do know what they were after adding them. With 6lbs of boost, ambient temp of 77 degrees, my plenum temps were 10 degrees hotter, around 85-90 degrees. With 8lbs of boost, they were in the upper 90's low 100's. Water temp into the core was 65-70 degrees. Low compression hyd roller combo making 820hp thru marine exhaust and accessories.

FWIW, a buddys non intercooled 10-71 making 8lbs, was around 140ish, and another buddys 10-71 making 10lbs, with intercooler, was around 110-115.

I didn't catch OP mentioned they were an hp 750 supercharger carb. It just stated 750 Holley. I guess I should have assumed as you did.

What should my intake vacuum % be at trying to choose correct power valves and tune carbs