I asked this before and didn't see where you tried this. Have you tried swapping metering blocks between the good and bad carb?

When you bought these engines, did the carbs come with them, and were they used carbs? If so you probably don't know the history behind them, and god knows what was done to them. I think the simplest (and cheapest) thing to do first is try to borrow a known good carb from someone (as Waybomb said), and see if that cures your problem. If so, then I would invest in new carbs, and maybe something a little smaller which will probably give you crisper throttle response.

The carbs did come with the engines. They were in a Sutphen 30 with Kamma drives and the guy I traded engines with had never run the boat, so god knows how these carbs even ran on that boat, much less a big heavy Stinger. They were also set up on a dual plane manifold, which would have definitely been better. I wanted new marine carbs along with this trade as well but he convinced me he could marineize the existing Demons and make them work with the package. The carbs were also never marinized with the j-tubes, making me want them gone even more.

Part of the trade included rebuilding these engines to Mercruiser 440 cyclone specs which is what they were from the start, I think they are close to that, but he shaved some of his costs by putting on cheap intakes, re-using his Demon carbs, using automotive pumps, and parts, and who knows what else. I just wish I even have the information on what is in these so I know whats going on with compression, pistons, cam etc. I know what is bolted on , but as for the guts I am not informed and I should be. I left it to him to do what was right and trusted him and his machine shop to build good motors, I now think I should have intervened more, but I'm no expert on what should be and what should not be. If I knew then what I know now. (the milk has been spilled, I'll stop crying now.....)

Just the induction system alone on the engines I traded to him are worth nearly the value of these base engines that still don't run right. I am starting to wish I ran the boat the way it was rather than get into all this troubble with the unknown, but I was afraid the engines I bought the boat with were a ticking time bomb, and I did not want the hastles and maintenance, and short life span on supercharged motors. (however reportedly this big heavy old Stinger 390 did over 100 MPH with the engine package I bought it with.) I am wondering now what I was thinking then. Who knows though, they could have blown up right away after sitting for 3 years or so. The things just scared me looking at them, my knowledge level and experience with blower motos is non-existant.

I'm sick of the crap that has become the relationship between me and this mechanic and the battles over the engines quality and service, now all I want is the mass of iron sitting in the back of my boat to do more than weigh it down. Nothing has lived up to my expectations or the arrangement we made, and I just want this thing running with no more battles. I have taken to doing everything myself and figure that is the best way for things to get done, and correctly, and the way I want even if I make mistakes along the way.

Thank you all for all the help you have given me with this project. This is my first performance boat and I am now on my own with it at this point, and learning something new every day both with experimentation and through this forum. Without this helpful online resource I think my learning curve would be much flatter than it has been. I figure if I keep throwing tools, time, and money at it ......it just might run! (unfortunately I am running short of all three)

Before and after pictures......

Okay, so the problems are definitly in the carb, so thats good. If I were you , at this point, I would do the following

Order two NEW holley 800 double pumpers.

Order two New marine fuel pumps

New distributor caps, rotors, and plug wires

New coils

New pickup sensors for the distributors

You will probably have to spend another 1500 bucks, but in the end, you should have a good running Stinger with all new components. It sounds like the mechanic kind of stuck you with some garbage parts. It sucks to have to straighten out someone elses shoddy work. I also know how it feels to throw money and time into something with zero results. Save some cash over the next few months, and get the correct parts you need. Do it first thing in the spring because you dont want to spend next season wrenching. You'll have your hands full gassing, cleaning, and enjoying the boat.

I know how you feel, trusting people to do the right thing, and being disappointed in the end. I have always been the kind of person who always did his own work, and I learned a lot along the way. Fortunately, most of my lessons were on cars and bikes (a lot cheaper). It seems like any time I thought something was beyond my skill level, and I sent it out, that's the item I usually had problems with. There are some great people out there who are honest, and do great work (a bunch are on this board). Just keep asking questions, you'll learn a lot from them. You'll get your problems ironed out, just try not to get frustrated. I would press the mechanic for the engine specs. I think once you really know what you have, you'll be in a better position to fix your problems, and the people on this board will be in a better position to help you. If your engines are mild, and you're not planning on revving them too high, you might be better off with dual plane manifolds. I'm sure there are plenty of guys on here that could give you better advice in that area than me.

Thunder,
I guess I was writing my previous post while you were posting yours.
I couldn't agree with you more. But, I think he should try to find out a little more about the engines. Given the way this mechanic treated him, who knows what's really in there. Pulling the intake and one cylinder head could really reveal a lot. A dial indicator, and a degree wheel could reveal even more. I don't know if he wants to go that far, but given the situation, I wouldn't be comfortable unless I did that. That's just my opinion though.

Paul

I'm wondering if 800's are even a bit too much. I can get a pretty good price on 800's, but I'm thinking 750's might be more appropriate. Will 50CFM between what I have now and 800's and / or between 750's and 800's make that much difference in performance, response, and fuel burn? Especially with a single plane intake that I have now?

I would like to replace the intake with a dual plane, however if the difference will not be really noticable than I would rather not blow the money on that right now. I think I need to see what smaller carbs will do, but how much smaller? I know the formula says a 750 should be plenty (and I'm sure these engines are not nearly 100% volumetric efficient) however Mercruiser orriginally put a 9022 800 CFM on the 420's and 440's, which makes me think that was the best match, or they just wanted the factory motors to run a little rich.....

I'm not really frustrated anymore since I think we have narrowed down the problem. I bought this boat because I wanted to wrench on the engines and learn something about them, which is exactly what I am doing, and could not be happier, although after all the work I have done I would like 1 or 2 nice rides this year. I am far more positive and far less frustrated than my wife for sure. At this point she would be elated if it blew up or sank (with or without me on it.... )

After read your post about the history, I am with Mild Thunder. As for carb size. I always like a little fatter carb.
And if you have time, I'd also do as Liberator says, if not for anything else but peace of mind.

I would go with the 800 holleys especially if you can get a good deal. They worked great on the 420's, and mine have the dual plane intakes. You should be able to get something back on ebay for the 850 bg carbs

This won't have anything to do with the problem but have you changed props since you've changed engines? This be part of your acceleration problem.

I'd yank the timing change cover, and get the part number off of the camshaft. Yes, it will be more time, but you'll save money in the end. With engines this size you'll be happier with dual plane intakes, and good 750's. You should be able to sell the open plenum intakes, and carbs for enough to pay for the intakes, and half the cost of the carburetors.

Regardless of if you don't care or not, keep in mind that the automotive parts on your engines will void your insurance.