Burning Twins

[Dean P]

Is it common for one engine to burn more fuel than the other? There is always a 0.3-0.4 difference in fuel consumption. If one (Rotax) engine is burning 4.6 gph the other is burning 5.0 gph. I replaced the spark plugs thinking this might help but made no difference. I burn 93 octane (most of the time). TIA

 

[swatski]

It would be normal in a Yamaha twin, as both impellers rotate in the same direction the load on the two pumps differs (from side to side). In a Yamaha, the STRBD pump works harder (and consequently maxes out at lower RPM at WOT) approximately 200-300 RPM difference (Yamaha used to pitch the two impellers different, PORT side with more aggressive pitch; albeit they don;t do that anymore).

Are your engines runnign at perfectly synched RPMs (across the range and WOT)? Just wondering.

--

 

[Dean P]

Are your engines runnign at perfectly synched RPMs (across the range and WOT)? Just wondering.

I should have noted that. Yes, they are in sync.

 

[Dean P]

@ScarabMike can you answer this? Is this normal?

 

[255IDTwin300s]

I noticed my 2 engines ( 300's) at anything below 5000 rpm ( which incidentally is when the S/C's start to come on) seem to be at times 6-700 rpms different. Then as soon as I go above 5k they are perfectly synched at the same rpms..

 

[Dean P]

I noticed my 2 engines ( 300's)

Stop bragging . I am concerned about fuel consumption. My RPMs are synced but one burns more than the other.

 

[255IDTwin300s]

Stop bragging . I am concerned about fuel consumption. My RPMs are synced but one burns more than the other.

Lol. I'm just wondering if at lower rpms your engines are at same rpms.. my engines are "synched" on the display button you can push to supposedly "synch" them to, but they are NOT at same rpms below 5000. "If" yours is doing the same, that could def make up or be a cause of diff fuel economy

 

[Beachbummer]

Have you considered swapping the engines from side to side to see if the problem follows?

(Sorry, j/k, could not resist)

Could be a load thing as suggested, but it would show for other boats too. Hopefully someone offers their experience to help.