I've never had twin tanks before I bought this Sonic......
One tank is port & one starboard. How do most of you use your tank switches to allocate fuel to twins.... one tank per engines? Feed both tanks to both engines simultaneously? Then switch to balance usage????
Expain your methods.... no owners manual was delivered with Too Old's Sonic!!

Around home I would pull from both tanks simultaneously. You know where you are and where your fuel stops are, etc..

The boat will not lean to one side or the other as it pulls fuel.

If I were making a long trek upriver or offshore, I think it is a good idea to maybe start on one tank and save the other for coming home? Just an idea.

WAIT!
-you're running twins. You got a built in mechanic!

OK, stbd tank to stbd motor, port tank to port motor. Usage should be identical. If you notice one motor burning more fuel than the other at fillup, it is a clear indicator of the higher usage motor being out of tune (plugwire shorting, choke sticking, etc).

Built in mechanic???? Built in insurance maybe, but mechanic??? Did I miss something???
Your usage of the switches is sort of what I surmised, but wanted to "tap" the well of knowledge!!

Had a electic controlled manifold to select any of 3 tanks for either motor. Never used it. Port for port, starboard for starboard, left the belly empty.
Gary

Blown

I guess you missed the "jist" of the built in mechanic.

If you run each engine off a separate tank, when you fill up any significant difference in the amount of fuel required to top off each tank is an indication of some malady regarding the state of tune of the motor burning more fuel. Granted, in a go-fast with rumbly exhaust, we all do a good job of ear-synchronizing our engines and we'll usually see the difference in our throttles. So the fuel difference is more of a redundant indicator. Also, we typically run WOT more often than other types of boats where we can easily see that one motor doesn't turn RPM like the other one. This still doesn't help diagnose cruise-speed specific issues like sticky choke plates (that will open fully at WOT but stay stuck at cruise), plug wires that are breaking down but still fire well enough, powervalve diaphragm problems (in Holley equipped boats), broken advance springs in the distributor (if you have a mechanical advance). There are a host of issues that will allow a motor to burn too much fuel at cruise while still allowing it to turn up well on top. Comparing one tank to the other can alert you to a problem that hasn't otherwise become obvious.

I know this is a very important way of keeping tabs on houseboat engines. Many of the houseboats out there still run points and condensers. They also have sloppy throttle cables and flybridge pilot stations that exacerbate the throttle cable slop. Comparing the positions of the throttle levers in relation to each other is useless on these boats. Furthermore, they do not see WOT all that often to compare the top rpms. Fuel usage differences noticed at fillup is the primary indicator of tuning issues. Adding the genset into the mix is an easy one also. It usually runs off one side and a gas genset typically burns around a gallon per hour.

By saying you have a built-in mechanic, I refer to the ability to spot fuel usage differences to point out tuning issues.

mcollinstn
You're exactly right about the mechanic. It took me 2 weeks to figure out why one engine of my cruiser was burning so much gas. The tach on that side was reading 500rpm low at cruise.
Gary

I have a 31 Sonic with the twin tanks run each motor on its own tank.....I have run one dry and switched over to run them both off one to get me in to the docks!!!

Ah!! I understand now what you meant by the B.I. Mechanic.
or also " active engine performance monitoring" could also be a apt phrase in that case. I was Thinking of 'how can twin tanks FIX a problem', not to help diagnose one.
Thanks for explaining what you meant......

Startin' this old thread back up!

Just picked up a previously owned Sutphen with side-by-side tanks, and the boat seems to draw from one tank at a time. The previous owner compensated with the tabs, but seems more of a band-aid then a fix. Should there be a valve somewhere to run both tanks at the same time? Where to begin looking? Thanks.

I always run one tank for a quarter of a tank and then the other. With the fuel injection I had to run double fuel controls because of the return fuel . At first I returned to only one tank. It got full!!