To repower or not part 2

If you want good economy and low running. Fit a 2 barrel or single barrel off a smaller engine. It gives good results for what you want. It won't have any top end power but you can't have everything.

 

Well I was catching up on my reading and Whitepointer beat me to the punch with his two barrel suggestion.

Of course you'll have the expense of replacing the manifold and there are not a lot of aftermarket 2bbl intakes out there. Most of the hot rodder crowd is going the other way and installing the 4bbls.

It would be worth looking into.

 

yes, very large float bowls, two of them with 4 floats on long arms.
They do not share connection with each other, so lets say all you run is on the primaries, the secondary fuel bowl will never be used yet will be full of fuel, and so it will rot in there which is a big problem if you use E10 fuel I think so.

You can mechanically lock out the secondaries and so then it will be a 2 barrel carb.
Secondary has an inner air valve, so carb CFM adjusts itself to engine cfm.

The power valve, I never noticed troubles with it. The vacuum spring rod simply pulls up when engine vacuum is high and drops down pushing the power valve open when vacuum is low, as long as it moves will be ok.

For cleaning carbs I use white vinegar if it bad, and 90% rubbing alcohol if it is not too bad.
Use a straightedge and feeler gauge to check for airhorn straightness. If warped, heat the top with propane torch to about 300*F - 350*F and it will relax the pot metal and you can clamp it down flat again. This works really well. But dont heat too much or the metal will all of a sudden collapse.

I also put Marine Stabil in the gas, it will help keep the corrosion away from the pot metal.

 

I've thought about the 2-barrel approach but then, how does it really save fuel? If you need so-and-so hp to spin prop so many RPMs, whether that happens at 1/8 throttle on a big carb or or half throttle on a little one, it takes the same amount of fuel, no? From what I can see the secondaries aren't opening at full throttle anyway, at least not in neutral. Maybe it needs load to crack them open. Or it's seized up. I wouldn't have any problem with plugging the fuel inlet with a bolt, but the secondary bowl feeds the idle circuit; there's a duplicate idle arrangement as in the primary side, which strangely enough also feeds the primary, but on the opposite side of the air horn.

Just today I was minding my own business after a week of cruising, and as we approached the marina, suddenly she refused to idle. I had to apply choke to keep it from stalling, by sucking fuel out of the venturis. She would rev up just fine, though. We roared up to a nearby beach and dropped the hook, and I pulled the carb apart (yet again). Cleaned out all the idle ports, put it back together, and she idled like a dream. what a PITA. I've already cleaned this thing like 3 times.

 

Sounds like you have tank and filter issues to. Start by removing tanks and clean or replace them. Fit a quality filter. Once you know the fuel is clean then worry about the carby. If your tanks can't be removed you need to figure out how to clean them in place. A bit of dirt causes a lot of problems. Thats what I would do anyway. Start at the tanks And work forward.

 

Yup. A lot of problems started when we sucked a tank dry. There's a new spin-on wix in there, but I want to install a clear inline one as well so I can see if anything is getting past the main filter. And yes, both tanks are coming out...

 

Are they easy to get out. Some tanks are a major pain when tbe boat is built around them.

 

Surprisingly yes, two smallish tanks with a huge access hatch to lift them through.

 

Thats a bonus.

 

The amount of fuel used will be the same only if the fuel to air ratio is the same. Too rich and more fuel will be used for the same amount of power. Too lean and the engine will run rough if it continues to run.

 

And hopefully the mix is right, or that's another issues.
Thanks everyone for your input. Before I decide if I should pull this beast I guess it behooves me to see if I can live with it running as best possible, and go from there. I might still decide to go that route, but if this thing can be made a little affordable...

 

I think your right about the secondary fuel bowl feeding non adjustable idle ports on the secondary side, I forgot about that. So the fuel will be slowly consumed out of the secondary bowl.

The secondary throttle valves are mechanical and will open when the throttle opens all the way, except if the choke lockout lever is engaged. The inner secondary air valve is just like the Quadrajet, opens with air CFM engine demand, so this is a variable CFM carb just like the quadrajet. Mine had issues and I went to a more modern carb design and have found it to be very reliable and the engines run better when the boat is rocking.
Maybe your secondaries are sticky with gums due to the bad fuel.

 

You know, sometimes you just need to cut your losses and start from scratch. That carb has been around for many decades. Consider biting the bullet (opening the checkbook) and installing a new marine carburetor of your choice. Get with a vendor you trust or call the manufacturer and insure that you're getting the proper product for your application.

Do you really want to spend your boating time worrying and playing around with an antique like this when there are alternatives available to you that will do the job? Replace that old part and with proper care you'll probably never have an issue again.

Good luck,

MIA

 

Generally, I agree with you, but after blowing a LOT of money for a new Holley that gave me no end of problems with my motorhome I'm pretty cynical with the new is better route, and this is especially on boats. In my last one I had a lot of original, 30 year old components still working, and I found when I replaced rather than repaired, at least 50% of the time the new component failed within a year or two. We lived aboard for 8 years and had a real chance to see quality of components. Too much stuff is sourced from the lowest bidder overseas with a local brand sticker stuck on it.

 

Another option maybe to find a low hour used mpi small block. Then you will have economy and power with hassle free starting and a sealed fuel system. No fumes.