Have a look at your props, could be they are different pitches or the stern gland on one side is tight causing extra load on that engine.

Do they have a return line back to the fuel tanks, could be that they both return to one tank not both, otherwise its in the tuning side of things.

Thanks Carnarvonite, I hadn't thought of the stern gland, I will check that the shaft can freely rotate. There are no return lines as such so can count that one out. Both props were made to order at the same time so should be ok...(I hope).

If it is the tuning side of things can a simple thing like a float level adjustment make the difference?

You should get a drop of water every 30 seconds or there abouts if its one of the older glands, just enough to lubricate the seal. If you give it a squirt or three of grease when you return to the pen it should stop the drip whole the boat isn't being used.

Float levels can increase fuel usage but not by as much as you describe and Id be getting someone to check out this whiff of petrol, its a perfect recipe for the boat to up with a huge bang'.

I have a feeling you are right, pretty sure the area under the gland is staying dry.

I hear you about the petrol smell - from what I can tell it's out from the exhaust like its either running with the choke partially on or something like that.

Thanks again

Swap the props over if they are not counter rotating and see if changes the consumption.  If it doesn't at least you know the props are ok.

B&##!er, I was hoping to not lift it out of the water for a while yet, oh well. Thanks for the suggestion Alfred, appreciated

You could start with pulling a spark plug off the engine. If it is brown and sooty then you know that you have a rich fuel condition which is likely related to your carberettor tuning.

If it is clean and white then the problem would be something else such as fuel leak or propellor setup.

check to see if there is an equalizing line that connects the two tanks .....fuel could be moving between the tanks....are you 100% sure that both tanks were full when you started....fuel flo meters have come down in price in the last few years, they are a very helpful tool for getting the best economy...good luck

Could be the taco is faulty. Try running the thristy motor with a bit less RMP or borrow a portable taco gun and check the RPM while cruising. Maybe the thirsty motor is running harder and the less thristy is not working hard at all.

CCC

Props would be able to be change with scuba escape. Are both motors in the same engine cowl ,Blocked air flow? will drastically increase fuel usage partially blocked air filters?.I am still thinking your tanks are linked or not balanced that is a huge difference.

Thanks everybody for the ideas.

I wont be able to get to the boat until the weekend but will do the checks everybody mentioned.

Georgejungle, motors sit wide apart in separate housings with reasonable vents. I will need to look at the tanks more closely, to see if they are joined in some way.

I wonder what would happen if I swapped the fuel lines over?

ccc, I do have access to the equipment you are talking about so can also give that a go. Maybe I do need to get fuel flow meters for reassurance.

Cheers

Just back from the Rottnest Convoy with over 4.5 hours on the water Saturday and with good conditions we were sitting on mostly 16 -17 knots. She is a thirsty beast but the fill at Rottnest this time was within 10 litres on roughly 125 litres a side.

Only thing I did was to back of the packing glands as per one of the earlier suggestions. I am pretty sure I had a blocked breather and an air lock the last time around.

Much happier now.

Thanks everybody.

No problems, all part of the service.

Definitely haven't got good looks going for me any more so have to rely on whats stored in the brainbox over the years.