Yamaha 90/65 jet 4 stroke / Octane

K

Kanadakid

Petty Officer 2nd Class
Joined
Dec 21, 2004
Messages
141
Ok found and learned somthing new this week. Have been running 89 gas in my 90/65 Yamha 4 stroke since last season. The boat runs 4900 RPMs at 34 MPH.<br /><br />This week I have been filling up with 87 and noticed a decline in RPMs @ WOT 4500 RPMs and 31 MPH.<br /><br />Yamaha reccomends 87 but this engine seems to get better performance with higher octane gas. I wonder what would happen if I moved up to 93 octane.<br /><br />Will it hurt the engine ? Based on this experience the performance 93 should get me to 5300 RPMs and 35 -36.<br /><br />Who else has a 4 stroke jet .....what has do you use ?<br /><br /><br />Thanks,<br /><br /><br />Kid
 
B

bigbrownbuku

Master Chief Petty Officer
Joined
Sep 17, 2004
Messages
885
Re: Yamaha 90/65 jet 4 stroke / Octane

4900 is low for that engine. check the impellor to housing clearance. could be the wrong impellor?<br />i will familiarize myself with jet wot rpm tomorrow.
 
K

Kanadakid

Petty Officer 2nd Class
Joined
Dec 21, 2004
Messages
141
Re: Yamaha 90/65 jet 4 stroke / Octane

Ben,<br /><br />Many thanks. I have a new impellor coming from the dealer. They just started making a new one with a different pitch. But yes the engine does seem a little slow RPM wise.<br /><br />It gets 33 mph on a 176 triton sport jet. The engine seems to run fine, it sounds OK.<br /><br />One thing is for sure, it runs better with 89 than with 67 octane.<br /><br />I really appreciate your help. <br /><br /><br />Kid
 
JB

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Yamaha 90/65 jet 4 stroke / Octane

Check your owner's manual, Kid.<br /><br />I suspect that it will tell you to run 87 octane minimum, and higher when available.<br /><br />Good luck. :)
 
K

Kanadakid

Petty Officer 2nd Class
Joined
Dec 21, 2004
Messages
141
Re: Yamaha 90/65 jet 4 stroke / Octane

I did. It recomends 87 and if the engine pings move higher the next highest octane.<br /><br />Kid
 
S

scout99

Cadet
Joined
Apr 25, 2005
Messages
6
Re: Yamaha 90/65 jet 4 stroke / Octane

K-kid I have a suzuki 90/65 jet I get 5500 RPM's but i do not know the speed. I would guess it would be just barely over 30. My dealer told me to use only 87 on my motor and that is what my owners manual recommends. Just trying to help you give you a reference
 
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