Starboard engine burning 5 gallons/hour more than Port engine.

barregus

barregus

New Member
Jun 3, 2009
18
Chesapeake Bay
Boat Info
2004 420 Sedan Bridge
Engines
Cummings 6CTA 8M
Last May I had 2 new carburators installed with tune-ups ( plugs, caps, rotors and wires ). I also replaced the ignition modules and coils on the motors ( paid the marina dearly - over $4K ). My problem is that my Starboard motor consumes roughly 5 gallons of fuel per hour more than my port motor. Motors seem to be running normally now, with no smoke, and synchronized at about 3150 RPM cruising.
Does anyone know what the heck can be going on to cause this huge a discrepency in fuel consumption between motors?

1997 330 Sundancer
454 Mercuisers FWC

Thanks!
 
My synchronizing gauge was way off on mine .:smt021
I now do it by the tach's reading only. :thumbsup:

 
Do you happen to have a generator?
 
I do have a generator, but that's not the problem because I haven't used it for about a year now.
 
I guess that would have been way too easy. My port engine burns more than my starboard. The port tank is the one used for the genny but even without running the genny I still burn more. I just had impellers and belts replaced yesterday. The mechanic said it is possible the belt slips a bit making it less efficient. I am not sure I buy that one but the belt did chirp a lot!
 
Pull each plug and see if they r all firing.... U may have a dead wire or plug and it's just dumping the fuel out the exhaust rather then burning it
 
Most boats have a dominate engine that burns a bit more fuel - but nothing like what you have going on.
 
How did you calculate that they're that much different? That's pretty fair sized variation for good running engines.
I'm not sure how your boat's set up but if you have seperate flow meters can you switch them (or the wiring) to see if the same condition exists? Or if they're vacuum, maybe switch the sensing lines?
If they really are 5 gph different it's probably a vacuum leak or bad part, not a failing engine.
 
The bigger question is: was there a measurable difference before you did the upgrades?

The reason I ask is that a number of things can cause one engine to burn more fuel than another. Shaft alignment can create more drag that consumes more horsepower and fuel.
If a problem like that existed before the upgrade it hasn't gone away.

On the other hand, if this is a new problem then I would start by swapping the carbs between the engines to see if the problem moves with the carb.

-John
 
@magster65 - I calculated the difference over the last 4 fill-ups by simply calculating time run and gallons used. I don't have fuel flow meters, but have switched tanks to see if if it was fuel tank related. Engine runs fine, although when cold it sometime stalls and runs rough ( something both motors do even with new carbs when they are cold ).

@PlayDate - there wasn't much of a difference before the new carbs were installed. I too am thinking of swapping carbs, but am waiting on the marina to see if they will warranty the work and carb. If not, I'll search for a better mechanic.

Thanks!!
 
I owned a 1995 330 Sundancer with 5.7 V drives and when I got the boat it consistently burned 20 gal more on the port engine than the starboard engine per fill up. I installed fuel flow on it and it confirmed what I already knew. I checked the prop's and it didn't make much of a difference. Then I had both carb's rebuilt and they finally came to within 1 gal of each other at a fill up. I made sure that the floats in each carb were set at the same level and never had a problem. It is possible that even though you had them rebuilt 1 level might be off from the other one. Just something else for you to try.
 
Thanks Chuck! My carbs are brand new, but I guess it's conceivable that there could be an internal problem from the factory. I'm waiting to hear from the marina to see if there is a warranty still left on these carbs ( I had them installed end of May last year ).
 
Just a thought and I may be way off base but a friend of mine had someone siphoning fuel from his boat at the dock. They always hit the tank on the dock side so he too appeared to have an imbalance in fuel burn when he really had no mechanical issues at all. Do you moor with starboard side to the dock?:huh:
 
Another absolutely dumb thought. But you know that the tanks are different sizes right? 110 and 115 gal to make the 225 total?

My starboard motor consumers more (per the gauge levels) then the port. The starboard tank is the smaller one and is the one that feeds the generator... Why the smaller one feeds the generator I have no idea.. Must be related to available space I guess..

I have always chalked it up to the size and out of sync conditions at times when cruising.. Perhaps we have the same problem...

But you are correct without precise fuel flow monitoring it's been a guess for me at best using hours run and gallons replaced...
 
If the carbs are brand new out of the box you definitely need to check the floats. I've replaced both of my carbs with Edelbrock 1409's and both had floats which were out of adjustment. It doesn't take much to not allow the float seat to seal well and allow additional fuel in. It's easy for them to get handled rough in shipping or during installation. When you check it make sure you check the float drop as well. You should also check your fuel pressure at each carb inlet - much beyond 5-6psi and you can overpower the float seats.
 
tdappleman said:
If the carbs are brand new out of the box you definitely need to check the floats. I've replaced both of my carbs with Edelbrock 1409's and both had floats which were out of adjustment. It doesn't take much to not allow the float seat to seal well and allow additional fuel in. It's easy for them to get handled rough in shipping or during installation. When you check it make sure you check the float drop as well. You should also check your fuel pressure at each carb inlet - much beyond 5-6psi and you can overpower the float seats.
Click to expand...

+1 :thumbsup:
 
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