I have 575sci's with Whipple intercoolers. These engines have always burned fuel evenly (within 1-2 gals on a tank of gas). Previous fill up one engine burned 12 gals more and this fill up it burned 19 gals gallons more (120 gal tanks). No extra soot in the tailpipes or black smoke. Checked the fuel tank valves to make sure nothing got bumped.

Any obvious things/areas to check? Thanks

Is your boat stored where gas can be stolen?

Whatch the kids with those lawnmowers.....They always have gas.....

Nope, it was in my shop the first go round. second time I watched one gauge hardly move and the other I could see dropping quickly. Went a filled up and came up with 19 gal diff.

The last time I ran across something like this it was a Cigarette where someone messed with the cross-over valves and both engines found it easier to pull from the same tank.

One prop has damage. Try swaping props, just be carfull how boat handles.
one motor has a problem, plugs, bad injectors (if injectors), bad valves or ???

Are both throttles run side by side or now you have to have one further forward then the other for the same rpm?

Both tanks getting topped off?

Throttles are side by side and I have not noticed any change in performance. I have another set of props I can try but they look fine.

I guess leakdown and compression checks are in my weekend forcast. Maybe swap MEFI and/or Throttle bodies??

If the motors are injected, check the air temp sensors. They do go bad.

Thanks, will that show up as a code in MEFI?

Thanks MT. The sensor was unplugged. I hd a few stern words with my mechanic.....ME