Twin outboards unequal fuel consumption

squidslayer

I think I posted this once before but....am still having the same problem and am taking to the dealer soon but would like anyones take on this issue.

I have twin 2007 Honda 150 Four Strokes with 300hrs on my C-Dory 255 Tomcat.
I get 10% to 15% more fuel consumption on the starboard engine than on the port engine.
I’ve tried trim adjustments….both are at the same rpm…
.For example on my Honda fuel management gauges…both engines.@ 3300rpm…the port engine reads 4GPH and the starboard engine reads 4.5 GPH. The starboard consumes more than the port at any speed.
Refueling I have confirmed this by measuring how much actual fuel the starboard tank takes as compared to the port tank. On full tanks if I need to fill 50 gallons to the port tank..I need 55gallons to fill the starboard. Both engines run fine but….. on a cold start the starboard engine is harder to start.
I know that I cannot expect EXACTLY the same fuel consumption in both due to factors like boat design ect …but 10% more fuel consumption in one engine over the other is excessive in my book..
I know someone who has the SAME boat as mine….. Tomcat 255… with the SAME 2007 150 Honda engines…with the same Honda Fuel Management Guages..he says he has double checked and that both his engines use the same amount of fuel equally.

Any help or advice or knowlege on this subject would be deeply appreciated.

Dick Enderle
Orinda, Ca

Da Nag · Posted: Thu Jan 24, 2008 9:19 pm Post subject:

Wild guesses on my part, but any chance your friend has counter-rotating props and you don't? I'll leave the real analysis to the engineers in the group, but here's a thought.

With the sideways torque induced by prop rotation, I'm thinking one engine will always have a slightly higher power requirement to keep the boat tracking straight. Counter-rotating props might negate this minor difference.

Another thought - any chance there is a slight mis-alignment in your engines? I'm assuming you have both set at the same RPM when cruising, but if one engine is straight and the other slightly offset, the offset engine will require more fuel for the same RPM's, no?

dogon dory · Posted: Thu Jan 24, 2008 9:19 pm Post subject:

Sorry, Folks - Post Deleted By Author

Alok · Posted: Thu Jan 24, 2008 9:55 pm Post subject:

I have a Tomcat 255 with twin 150 Suzukis and counter-rotating props. I have noticed the same thing- the starboard engine uses up to 10% more fuel than the port engine.

This has to be a characteristic of the Tomcat. Does it have something to do with the list to starboard that all Tomcats seem to have? This might affect the angle of the motor while running and increase the load on the starboard prop...

What is even more surprising, just as Dick states, the starboard engine on my boat also gave me trouble in cold weather last winter. A couple of times, it stalled within minutes of starting. I remember calling the dealer concerning the problem. This has to be a coincidence! Interestingly, this winter it has been OK.

squidslayer · Posted: Fri Jan 25, 2008 12:31 am Post subject: counter rotating

I have counter rotating engines...plus permatrims..hmmmm I wonder? could the permatrims be the issue??

Dick

rogerbum · Posted: Fri Jan 25, 2008 12:42 am Post subject:

Is the boat running completely level? As others have suggested/hinted at, it may be that one engine is doing more work even though it is at the same RPM's. Someone recommended a dash mounted level a few months ago, it would be interesting to see if simply trimming the boat to level would even out the consumption.

Alok · Posted: Fri Jan 25, 2008 10:10 am Post subject: Re: counter rotating

matt_unique · Posted: Fri Jan 25, 2008 10:30 am Post subject: Hmmmm

Discovery · Posted: Fri Jan 25, 2008 10:32 am Post subject:

We have counter rotating Honda 135's. I have the same fuel consumption issues. The starboard engine uses a little more fuel.

tsturm · Posted: Fri Jan 25, 2008 11:02 am Post subject:

Maybe the port engine is running 10% leaner than the starboard, slowly committing suicide Wink

Maybe a prop is dinged, more weight on the starboard side, maybe your friend with two engines that use exactly the same amount of fuel hates you?
Have a good one!! Mr. Green

Les Lampman · Posted: Fri Jan 25, 2008 1:56 pm Post subject:

I don't have a specific answer for this either but my "gut" reaction is that since the counter-rotating engine is typically installed on the starboard side on the Tom Cat that it's something to do with that. The only reason the counter-rotating engine rotates the other way is there is a small intermediate gear in the lower unit of the counter-rotating model that makes it shift the opposite direction. So it seems it would either be that the engine for whatever reason is a bit less efficient in that mode, that the LH prop doesn't work quite as well (I've noticed I can almost never get exactly the same WOT rpm from the engines), or that the list on the boat is creating more drag on the starboard hull. Of course, there are lot more possibilities...this is just a start.

You could, really without much trouble, swap the two lower units and see if that changes anything. There isn't anything to connect or disconnect, when the bolts are removed the lower unit slides off.

You might also make sure the two props are really pitched the same. In having several new props checked it's amazing sometimes how not alike they really are (or aren't).

Ah...and the toe-in and/or toe-out of the engines could cetainly change the load on the props as well.

Da Nag · Posted: Fri Jan 25, 2008 3:56 pm Post subject:

Maybe if you cruise in reverse half the time, it will even things out.

Thank you, thank you...I'm here all week.

matt_unique · Posted: Fri Jan 25, 2008 4:34 pm Post subject: Gearing

dogon dory · Posted: Fri Jan 25, 2008 5:02 pm Post subject:

Sorry, Folks - Post Deleted By Author

dogon dory · Posted: Fri Jan 25, 2008 5:35 pm Post subject: Re: Gearing

Sorry, Folks - Post Deleted By Author