That's what I thought, turned out to be a load issue going from small props to big props...

Odd, you woukd think it would mean out, I may play with it to see one day

Hard to say what's going on with that 4x8 FA vs none.

Air direction thru the boosters and over the air bleeds can help or hinder the carb's fuel metering which obviously can help or hinder a/f ratio's....even though our brains get stuck on if a FA or Air Cleaner (cars) flow enough air.

Way back when I was semi cool and had half a life (single) I spent almost every Friday night at the track....I spent lots and lots of time tuning and trying things for + and - results. Okay, always trying for + but of course would run into alot of -'s. With my cars and with many other people's cars. Beauty of the track is that you can measure results in the form of ET and mph.

Had a car (sleeper) for a while that had very little room between a small air cleaner and the hood. Figured out quickly the air cleaner was restrictive and the top was too close to the fuel bowl vents after trying many different drop base air cleaner assemblies, flat base, slightly raised and etc.....in almost every case the carburetor needed slight re-tuning to get best mph (horsepower) for the change. No air cleaner always proved to be the best. Until, for whatever reason, I left a certain drop base bottom on it, and car responded with higher mph then any of the other set ups. Interesting and yet another thing that made no sense but it worked better.

Anyway.....testing, tuning, testing, tuning, on and on......leads one to squeezing the most power out of one's set up.

Add to that.....vehicle (not engine) tuning also. Boat, car, snowmobile, tractor,.....doesn't matter.....most everything will have added performance hidden in areas we think we know and area's we don't know.

How much you care and how much time you want or are willing to spend will most likely influence how much extra performance you ring out of your form of vehicle. Note: It doesn't always end up where you want, but that's life !

So....lesson in all of this is learn from others and try different things on your own. Back to learning from others - never take everything as 100%. Why ? What works for one does not always work for another. Keep what is said in the back and frt of your mind. Try what they say but don't expect it to always be the best. I can't tell you how many times what worked for someone worked for me alsoand I can't tellyou you how many times what worked for someone else didn't work for me. And vice versa of course. Thus why , in person, one will here me say many times, "try it ! "

Props
Drive height
Weight placement
Engine mods
Engine tuning
Engine compartment airflow
How you drive ! Ask someone with a faster than others with same boat pad or step bottom boat how important this is !
etc,etc, etc, etc

Totally get it, that's why I am going to fine tune in the boat the best I can and maximize my parts, hoping to see 74-75 when done and that's not bad for a mistress at all, then if still reliable I'm happy .

In the world of 2 stroke mx/atv motors which are much more effected by changes, what we found was that people were pulling the factory airbox and intake tube and replacing with a "sock" filter right off the carb. and it had a negative effect. getting had to be richened drastically. Now if you put a 6" tube between the carb and filter, you didnt need to richen the jetting and it ran better.

Why? With the tube the same amount of air was entering the carb, but velocity/direction was better making for better metering/draw thru the jets. without the "velocity stack" there was a lot of turbulance over the jets decreasing metering.

Im all about the airflow. Everybody today is running bigger HP engines, and airflow is always like some sort of neglected step child. Everyone is scared of a dominator carb, bilges designed around 400hp lacking fresh air and feeding carbs hot air, and so on.

I have some fairly open race style hatches on my boat. Even with a roots supercharger, without the intercooler, temps in the intake manifold around 140 degrees. With intercooler, low 100s. Id be willing to bet a few beers, tims NA 540s, with stock sunpad, is probably seeing intake temps as high if not higher than my supercharged mills.

Cold air isnt just for forced induction! All gas engines love it. Endeavor32's bilge air flow thread has some good info

Yes I agree and it seems at times I see a little more lean with hatch open 6" and staring at air fuels, other times I don't see a change, that tells me I am right there with airflow and temps, as you know in our talks we are looking at options for addressing that with my difficult hatch space to be able to add venting, that's another thing I am going to address while "maximizing all issues" lol

It was a very short experiment, but yea. As Phragle mentioned, an open carb isn't going to give you the best air available. What I saw wasn't just a rich AFR, but an erratic one, and that tells me that even though more air was available it was turbulent and actually hindering the air moving in. I believe a velocity stack would've helped a lot to smooth out the air flow, and I'm just taking a guess here, but perhaps the filter adds a little tension to the air straightening it out allowing more mass of air to fit. Imagine a hundred people scrambling to fit into a train car and how chaotic that is. Now imagine them filed up in rows entering the car in a much more orderly fashion - a denser mass fills the car quicker. I believe just a little bit of tension on the air actually helps straighten it out allowing a denser mass to fill the space quicker.

For sure.

OK, so the issue turned out to be the port engine needeing much less jet then Starboard, with the small props it was less load and would spin 5900, therefore cleaned up due to using more air then at 5500, I leaned out the port engine more and they evened out, saw 72.2 last weekend @5500 both even and didn't have it fully trimmed out...air fuels still high 11's WOT, cruise is right around 12.0-12.4 A/F.... not sure how I can lean out top end more without making cruise A/F unsafe.... I have quickfuel 1050's if anyone KNows anything about ho to deal with airbleeds and if they change cruise A/F also??