Fuel consumption

F

firstlight

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I have new twin 454 Mercruiser long blocks with new carb's. running both engines with dash tacks reading 3100 rmp's I consume 30% more fuel on port engine.
If I use the glendining Synchronizer running at 3100 the port engine reads three hundred rpm's less on instrument panel tack then the starboard
Which would be more acurate tack or synchrinizer and could that be fuel consumption problem. Thanks Frank
 
I had a similar problem with the Rochester Quadrajets.

one of the carbs had the wrong metering rods.

took a lot of detective work.

RWS
 
a number of things could be going on but first you need to get a photo tach and calibrate your tachs.
most likely your tachs aren’t correct and when you are running 3100 without the sync the port engine is doing more work thus using more fuel. when synched they are probably using the same fuel. your stbd must be the master. Does the boat turn toward stbd at 3100?
 
Don't laugh..... try tapping the face of your tach with your finger next time your at 3100 rpms like your trying to wake it up. tap pretty hard.

Once in a while my port tach would read 500 rpms faster than the other. It would freak me out as I thought my transmission was slipping. Tapped the tach face and they went back together.

Weird but true. Cant say this is your problem, but it once was mine.
 
quote:
Originally posted by JLC

Don't laugh..... try tapping the face of your tach with your finger next time your at 3100 rpms like your trying to wake it up. tap pretty hard.

Once in a while my port tach would read 500 rpms faster than the other. It would freak me out as I thought my transmission was slipping. Tapped the tach face and they went back together.

Weird but true. Cant say this is your problem, but it once was mine.

Click to expand...

Not funny, it happens to my tach sometimes too. The contacts are dirty and Faria said they would rebuild it for me but they would not re-calibrate the engine hours back in it so I have just been dealing with it. There is a screw on the back on mine that is for 4/6/8-cylinder settings and when I dail it back and forth a dozen times or so it will last the season with no issue.
 
Since the tachs disagree with the passive sync indicator, I certainly agree with checking both tachs with a photo tach or dwell/tach or digital timing light with tach feature on the engines, as well as rotating the tiny switch on the back of the tach for # of cylinder settings to help clean it's internal contacts. Note what the setting is before your do that , and whether the 2 tachs are set the same as they should be. I'd believe the sync indicator over the tachs.

But I'd also suggest confirming the engines are running on independent tanks and lines, with any crossover valve always left CLOSED except for emergency fuel supply. An open crossover valve can easily cause a 30% difference in total fuel drawn from one tank vs the other(though not always.)

You could also use a timing light on each plug wire to confirm at least all plugs are firing, though not necesarily proving combustion.
 
Can't you hear when the engines are synced? I cant stand it when my engines are out of sync. You shouldnt need an instrument to tell you.
 
OHB- FWIW, I can very easily audibly detect sync of the I/B's from my marlin tower but for some reason , possibly audio overload with my tinnitus, not from the lower station. That's why one of the reasons I love my active Accusync system. Sometimes syncing by ear just doesn't work for some of us.
 
The tach for my starboard engine is often way off. I go by the synch and the sound instead. I've played with the 4/6/8 switch in the back a few times and it clears it up for a while, but it eventually comes back. I'll probably just get a new set of tachs eventually, but I've sort of learned to live with it for now.
 
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