Have a stock 460 with new 850 cfm 7481 mechanical secondaries.  Idles and  runs ok at 3500 rpm but if i step on it, bogging.  Suggestions please.
 On vacation on the water but not running right. 

Pull a plug and post a pic.

More often than not, they will be lean at the top end.

I recommend picking up a 4.5 power valve and some fatter jets.

What's the list number on your carburetor?

GT

Here is a pic.  I did purchase a 750 with vac secondaries and it runs much better. Still only doing 4,300 rpms @ 43 miles per hour 21' Boss Day cruiser.  Your thoughts?

Whoa!!! Stop running it!!! You need a lot more fuel!!! That is way lean!!!


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It idled for a minute or too.  Parked the boat...  850.

Plug reading at idle is pretty useless.. IMO

GT

Sorry.

HAhaha.. For what?

I wish i wouldn't of idled after the run...  not sure what the jetting is but national carburetor told me 850 was to big. I couldn't wait for the jets so, i purchased a 750 non marine to get me buy.  Vacation is not time to have issues.  :-)

True that... National carburetor? Who the heck are they?

Look them up. :-)  the 850 is new and i'm working with them to figure out issue.  Calling them tomorrow.
Your thoughts on adding j-tubes to the 750?

The 850may be for sale.:-)

Is the 750 vacuum secondaries?  Those are usually more forgiving to engine size application. 
How did you set the floats on the 850?
850 is huge for stock 460 but shouldnt cut out sounds like lack of fuel
Go back and start over
Step#1 set floats remove sight plug loosen lock screw turn adjusting nut until fuel level is at bottom of sight plug hole.  Clockwise lowers counter raises fuel level
Step#2 set "Curb Idle" turn idle screw 1-1/2 turns from having the plates seated in the bores is a good rough setting. 
Secondary idle speed adjustment is 1/2 to 1 turn away from plates seated in the bore.
Fast idle adjustment is made with fast-idle screw on highest step of the fast-idle cam.  Clearance between the primary throttle plate and the throttle bore should be 0.025 inch.

So, looking into National Carburetors, IDK bro.... Seems very Auto Zonish to me.......

Not hatin', but not likin' much either.