• Welcome to Jetboaters.net!

    We are delighted you have found your way to the best Jet Boaters Forum on the internet! Please consider Signing Up so that you can enjoy all the features and offers on the forum. We have members with boats from all the major manufacturers including Yamaha, Seadoo, Scarab and Chaparral. We don't email you SPAM, and the site is totally non-commercial. So what's to lose? IT IS FREE!

    Membership allows you to ask questions (no matter how mundane), meet up with other jet boaters, see full images (not just thumbnails), browse the member map and qualifies you for members only discounts offered by vendors who run specials for our members only! (It also gets rid of this banner!)

    free hit counter

Burning Twins

Dean P

Dean P

Jetboaters Admiral
Messages
3,471
Reaction score
4,915
Points
357
Location
Florida
Boat Make
Chaparral
Year
2017
Boat Model
VRX
Boat Length
22
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

swatski

Jetboaters Fleet Admiral 1*
Messages
12,806
Reaction score
18,566
Points
822
Location
North Caldwell, NJ
Boat Make
Yamaha
Year
2016
Boat Model
AR
Boat Length
24
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

Dean P

Jetboaters Admiral
Messages
3,471
Reaction score
4,915
Points
357
Location
Florida
Boat Make
Chaparral
Year
2017
Boat Model
VRX
Boat Length
22
swatski said:
Are your engines runnign at perfectly synched RPMs (across the range and WOT)? Just wondering.
Click to expand...
I should have noted that. Yes, they are in sync.
 
Dean P

Dean P

Jetboaters Admiral
Messages
3,471
Reaction score
4,915
Points
357
Location
Florida
Boat Make
Chaparral
Year
2017
Boat Model
VRX
Boat Length
22
2

255IDTwin300s

Jet Boat Lover
Messages
40
Reaction score
51
Points
77
Location
Orlando Area
Boat Make
Scarab
Year
2019
Boat Model
Wake
Boat Length
25
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

Dean P

Jetboaters Admiral
Messages
3,471
Reaction score
4,915
Points
357
Location
Florida
Boat Make
Chaparral
Year
2017
Boat Model
VRX
Boat Length
22
2

255IDTwin300s

Jet Boat Lover
Messages
40
Reaction score
51
Points
77
Location
Orlando Area
Boat Make
Scarab
Year
2019
Boat Model
Wake
Boat Length
25
Dean P said:
Stop bragging :p. I am concerned about fuel consumption. My RPMs are synced but one burns more than the other.
Click to expand...
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

Beachbummer

Jetboaters Admiral
Messages
3,963
Reaction score
2,882
Points
332
Location
Houston TX
Boat Make
Yamaha
Year
2008
Boat Model
SX
Boat Length
23
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.
 
You must log in or register to reply here.
Top