Fuel System setup question

[Hart]

My fuel system consists of two primary 125-gallon tanks (somewhere around midship) and two 50-gallon "auixiliary" tanks aft. The copper fuel lines from each run to a central manifold with a crossover, so each tank can be isolated, port engine can run off starboard tank(s) and vice versa.

Two weekends ago, while trying to equalize fuel levels in the primary tanks (the starboard was about half full, the port a bit over three quarters full) I had the forward port tank isolated as the only open fuel source with the crossover on, so both engines were running off that single tank. A short time after increasing speed to WOT I lost juice. It took us about 15 minutes of fiddling around with the valves, etc to get fuel flowing again. We pulled a spark arrestor off the port engine and the carb was bone dry; there was no fuel flow.

Captain J thought that the issue was pulling air from the empty port auxiliary tank and flooding the system with air instead of fuel. This explanation seemed sensible at the time because another friend on board started opening/shutting fuel valves, and at that point I wasn't entirely sure of myself as to exactly which tanks were on and which were off. My brother confirmed for me last night that after we got the boat back into port over Labor Day, he isolated that forward port tank to equalize the fuel level (Hart's Desire is listing a bit to port from the extra fuel weight). I thought that was the configuration of the manifold valves when we left port for the ride where we experienced this problem.

My brother's theory was that both of those 440s running at WOT couldn't pull enough fuel through a single line to feed both engines (even though the crossover was clearly open). I thought my broker may have sent me a message similar to this when I advised him of the issue. The engines seemed to run fine at slower speeds - they had been running for about 15 minutes before we came up to speed.

So, is it likely that both engines can't run off a single tank at higher speeds? Or do I have a potential clogging issue on the primary, port tank? The fuel level is dropping, so I don't think that's it. I think I simply learned a lesson about how these engines react to certain valve settings in the fuel system.

Any input would be appreciated. Thanks.

[Stripermann2]

On this set up, be sure which ever tank or tanks you draw from, the others are closed off. Yes, it will draw air from an another tank. Draw from the front tanks, close off rears...draw from a single tank, close off other three.
If the center cross-over valve is NOT shut between two tanks, the tank with more flow will provide fuel for both engines, there will be no equal drawing from both, as you might expect.

You should be able to draw from a single tank with no issues. Along this thinking, be sure the anti syphon valves are not clogged as this will be evident by limiting fuel quantity under load demand.

[The Dog House]

Engines will definitely draw from different tanks differently. I have a single 318 with a port and starboard fuel tank. The port tank has an approximately 3 foot run of copper tubing to the fuel filter while the starboard tank has an approximately 10 foot run of copper tubing to the fuel filter. I started with both tanks full and both fuel valves open. After approximately 2 hours of running, I refueled and put 22 gallons into the port tank and 1 gallon into the starboard tank. The engine definitely preferentially draws from the port tank. The engine runs fine when I have the port tank closed and the starboard tank open, so it is not a fuel restriction issue. My only guess is that the increased resistance due to the longer fuel line results in the difference. I just make sure to only run on one tank at a time and switch tanks before they run dry.

[prowlersfish]

Sometimes when you try to draw 2 engines from a single pick up sometimes there can be issues . The pick up maybe 2 small for 2 engines at speed ( high flow demand )

[Hart]

Sometimes when you try to draw 2 engines from a single pick up sometimes there can be issues . The pick up maybe 2 small for 2 engines at speed ( high flow demand )

This is kind of where we're at. However, would this issue result in basically bone-dry carbs? Seems there would still be SOME fuel flow where we apparently had none, but......I'm no mechanic by any stretch.

[DAVIDLOFLAND]

You should be able to draw from a single tank with no issues. Along this thinking, be sure the anti syphon valves are not clogged as this will be evident by limiting fuel quantity under load demand.

+1

[kallen]

Are the aft tanks not considered primary tanks & the mid-ship ones are auxillary?

[Stripermann2]

Primary...secondary. It really doesn't matter what you call them. Trojan originally only had the front tanks, outboard of the engines, with the aft tanks as options. Later, they added them as standard configuration.

Dependent on a sea's state, vessel loads, etc...some folks will use the fuel from rear tanks first, some from midship... to trim out the boat. I mix it up.

[prowlersfish]

Primary...secondary. It really doesn't matter what you call them. Trojan originally only had the front tanks, outboard of the engines, with the aft tanks as options. Later, they added them as standard configuration.

Dependent on a sea's state, vessel loads, etc...some folks will use the fuel from rear tanks first, some from midship... to trim out the boat. I mix it up.

On the F36 the front ( side tanks ) are the mains and the rear tanks aux and were a options

I thought it was the opposite on the F32 . ????

[Hart]

Are the aft tanks not considered primary tanks & the mid-ship ones are auxillary?

No. On my boat, the forward tanks are the primaries at 125 gallons each. The aft tanks are auxiliaries at 50 gallons each.

[Stripermann2]

Primary...secondary. It really doesn't matter what you call them. Trojan originally only had the front tanks, outboard of the engines, with the aft tanks as options. Later, they added them as standard configuration.

Dependent on a sea's state, vessel loads, etc...some folks will use the fuel from rear tanks first, some from midship... to trim out the boat. I mix it up.

On the F36 the front ( side tanks ) are the mains and the rear tanks aux and were a options

I thought it was the opposite on the F32 . ????

Same... Think teak rear cockpit and the inaccessiblity to aux tanks. You'll notice the standard wasn't until serviceable and removable decking.

[captainmaniac]

Primary...secondary. It really doesn't matter what you call them. Trojan originally only had the front tanks, outboard of the engines, with the aft tanks as options. Later, they added them as standard configuration.

Dependent on a sea's state, vessel loads, etc...some folks will use the fuel from rear tanks first, some from midship... to trim out the boat. I mix it up.

On the F36 the front ( side tanks ) are the mains and the rear tanks aux and were a options

I thought it was the opposite on the F32 . ????

Same... Think teak rear cockpit and the inaccessiblity to aux tanks. You'll notice the standard wasn't until serviceable and removable decking.

Maybe that changed when they lost the teak aft deck. In my '79 the aft tanks are the primaries (and there is a reasonable sized hatch providing access to steering / tanks / water tank and pump / trim pump / aft bilge pump etc as needed, or the whole cockpit sole can be lifted off in one piece to get the tanks in or out); the optional second set of tanks were forward beside the engines.

[Stripermann2]

Captainmaniac and Paul are both correct. The older F32's main fuel tanks were under the cockpit. The optional fuel tanks were added to the hull sides outboard of the engines.

[summer storm]

Captainmaniac and Paul are both correct. The older F32's main fuel tanks were under the cockpit. The optional fuel tanks were added to the hull sides outboard of the engines.

That's correct the 32 had two 60 gallon tanks aft as standard and two 50 gallon in the engine room as a option.