While it is true that the fuel pressure should be regulated to 7 lbs., if the needle were off the seat , the fuel level in the bowls would rise until it poured out of the vents. Maybe that's happening at higher rpms. Something to check but I don't think so.

If those are automotive fuel pumps like you say, Running them in a boat is a NO-NO!! Break down and buy the marine pumps, before you blow up!
They should have a closed vent system connecting to the carb with a small hose.
Also, in my opinion, Blaster 2 coils suck. I've had a few of them go bad on me (primary side open), for no apparent reason.

I know all about the differences in marine vs auto parts, but I'm trying to get it going with what I have. I have all winter to marineize. I just with the marine mechanic who put this thing together has used marine parts instead of trying to save himself money and throw auto parts on marine engines. Thats a whole other issue with this job.

Today I added fuel pressure regulators, changed the oil and replaced the carb power valve again, just to be sure after a few more pops while adjusting the other day. I ran the fuel down to nothing , added new fuel, replaced the fuel filters and went for a ride.......all in vain. No change in performance or lack thereof.

I'm going to try blowing the carb out again, cleaning the pickup tubes and anti-siphon valves, and perhaps advance the timing a few degrees to see if that will make a difference. I don't have the cam specs so I don't know exactly what advance this cam likes, and I can't get a response from my old mechanic about the details.

I have thrown lots of time and wrenches at this thing, I figure it's time to throw some money at it and invest in new carbs. Not an expense I wanted but I can't keep chasing my tail over this and wasting day after day trying to figure it out. I also have spent enough in fouled plugs to pay for 1/3 of a carb.

I'm thinking I don't need anything bigger than 750's perhaps an 800, for my low rpm application. Perhaps even vac secondaries in the interest of efficiency. Any opinions on this?

Thanks for all the advise on this frustrating problem. Hopefully it will come to an end soon.

My comments on carb size - having carbs, say, rated 100 - 150 cfm higher than you need would not cause the problems you are having. I just looked at a chart that shows an 850 is perfect for a 454 at about 6500 rpm. 750 seems good up to about 5500 rpm. But a little overcarbureted won't cause the problems you are having. What about accelerator pumps - are they leakinginto the carb? Can you borrow a known working carb from a buddy and try it out?

Have you checked compression? Next time you pull all the plugs, do so and report your numbers. And are you sure you are getting a hot spark at all plugs at the correct time, all the time?

Did you change the oil leaker coil? How bout those caps? Waybomb is right, youre a little overcarbed, but nothing that should cause your symptoms. I'd still look in the ignition system for a little while and give the fuel system a break. Dont get discouraged, its probably something really simple

If you do change carbs, stick to a square bore,double pumper type carb. I had 800's on a pair of 454/420's and they worked great.

850's are too large for optimal performance, but should not be causing this problem, especially if you've swaped carburetors, ant the problem followed the carburetor? Have you swapped them back yet?

The first thing to do would be to take the carburetor apart spray out all of the orifices in the main body, and metering blocks with some carburetor cleaner and compressed air and try it again. Now re-try it at the dock. Carburetors are extremely simple, if there is a problem there is either too much fuel, or not enough. Put the engine in gear (tied to the dock as you have before) and bring it up to the RPM it is having a problem. Now press on the accelerator pump arm. This will add fuel without changing the amount of air the engine has, and will either make the problem better or worse. It may not solve the problem, but it will let us know what to look at.

Took the ailing carb off today and swoped them again motor for motor.

I took the suspect carb to dad's shop where I had everything I needed. Hit it hard with carb cleaner, compressed air in every hole I could find about 12 times each and from every angle. Cleaned the transition slots, and blew out every hole on the carb body. Re-gasketed and put it back together. Put it on the boat and took it out after re-checking timing, and settings etc. I did not run the engine in the river until I got out. I warmed it for a few minutes and brought her up on plane. It was hesitant to accelerate, but reached a new weekly high of 2900 RPM's and no higher. Average was 2600 or so. It just did not have any guts to it at all. The other engine accelerated mostly normally. The problem followed the carb to the port engine!

I slowed her down after a few minutes of trying to nurse the power in, and checked the vacuum readings of the two engines. The port engine was showing a larger drop in vacuum under load, and would not accelerate but only chug along. The stbd engine had higher vacuum under load by a few inches at the same rpm (1500 or so) When I goosed them together I could get the port engine to accelerate only up to 2600 RPM and it really did not want to go. I brought it to idle and it would idle all day long. I shut it down for the ride back to the dock.

It was still running extremely rich evidenced by a fuel slick in the exhaust and real smokey running. The 4 corner screws are almost all the way in. Highest vacuum was with the screws all the way in and I would then richen by 1/4 to 1/2 turn. Any more turns out and the engine would want to die. I also advanced the timing a few degrees to try to lean it out a little but that had no effect. The book says 36 degrees total advance, but that seems too high to me so I kept it around 12 base which gave 32-34 total. That seems to be the best place for it.

I think it's time to pony up the dough for a few new carbs that are more appropriate for this setup. It seems these 850 Speed Demons are just too big for what I have. Not to mention I used nearly 20 gallons of gas (by the gauge) for a 5 -10 minute time on plane at 2600 and 3000 RPM respectively, and idle on one engine to and from the dock for a total of about 40 minutes. This seems extremely excessive for this kind of setup. I can get a nice price on a rebuilt set of 0-9022 marine Holleys (800's) locally and just may do that. I'm wondering if the 0-9015 750 carb would be a better choice though for my application. I really wish I knew the cam specs to help me decide. I'm thinking only 420 - 450 HP tops, at 5000 RPM and below. The mechanic said the cam was 0 overlap with a slightly higher lift for tourque, and I think he said they are Crane Cams. I know almost nothing about camshafts and how I should pick my carb, intake, and set timing based on the cam.

Thanks to all, I'll keep you all advised.

Go to www.holley.com. You can access their charts there. I think a 454 at 5000 r's is 700 or 750.
There must be something radically wrong with that carb you have. There has to be a blocked passage, and accelerator pump check busted, or a real crack in the casting.
I still believe the carb size is ok - the other engine runs fine, correct? If you've relegated yourself to buying anew carb, and I would probably do the same after what you've bennthrough, I'd buy a duplicate of what you ahve on the good running engine. Only buy one carb; why two.
But me being me, I'd be going through that bad carb with a magnifying glass. I'd wanna know what's up doc.

I just read you have a single plane intake manifold. With that, I would say the 850 is too big. 750 will work much better. I am sure there are people who are successfully using an 850 on a 454 but more likely than not, its on a dual plane.