Reply
 
Thread Tools Search this Thread
 
Old 25 September 2004, 16:57   #1
Member
 
Country: Norway
Town: lillestrøm
Make: bombard 550
Length: 5m +
Engine: yamaha O.B. 75
Join Date: Sep 2004
Posts: 22
oktane???

I have a yamaha 75 hp OB. 92mod this is a enduro, a lowcost mod. (probably sold in Sweden) without el. starter.
My question for the crowd is: have you eny experience with low vs. high octane on this engine.
My choice is to go for 98 oct but since i can´t find eny info in the manual i wonder if others have had problems regarding this issue.

This is what i have dicovered during the last 3 years (octane related)

with 95 oct:
-kicback in start line at warm engine(arm= )
-at high water temp and after a while with high power, the engine misfires
and it seams like the ignition is to far advanced , no power at all over
1500rpm
-lower power in general
-more expencive to feed

with 98oct
-starts easier
-runs smoother
-more power (rpm+ 300 5knots )
-runs cheaper
-more expensive fuel (+5-7%)

In Norway we can still get 98 oct, but they are talking about skiping the 98,
and have the 95 as the highest

What i have heard is that they have stopped selling 98 in Denmark, how is it in
UK (and the rest of the world)????

Let me know please!
__________________

__________________
pellesmil is offline   Reply With Quote
Old 25 September 2004, 18:20   #2
Member
 
Country: Sweden
Town: Stockholm
Boat name: Osprey & Ring
Make: Osprey & Ring
Length: 9m +
Engine: Plenty
Join Date: Mar 2003
Posts: 860
Tjenare pellesmil;

Sweden still have 98
__________________

__________________
www.grandrib.se
Petrov is offline   Reply With Quote
Old 25 September 2004, 19:21   #3
Member
 
Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,962
I'd be surprised if you require more that 92octane (RON) for such an engine. It sounds as though you possibly have a fault or a mis-setting. From what you say, it may well be over advanced.
__________________
JW.
jwalker is offline   Reply With Quote
Old 25 September 2004, 19:37   #4
RIBnet supporter
 
bogib's Avatar
 
Country: Iceland
Town: Reykjavik
Boat name: Cheesee
Make: Seaquel 600 XS
Length: 6m +
Engine: Mercury 275 Verado
Join Date: Aug 2003
Posts: 1,959
Send a message via Skype™ to bogib
We have choice of the following
92
95
99+

Bogi
__________________
RIBs and ribbing is my life
www.sjosport.is
bogib is offline   Reply With Quote
Old 26 September 2004, 06:17   #5
TIM
Member
 
Country: Ireland
Town: Dublin
Boat name: WIZARD
Make: REDBAY 7.4
Length: 7m +
Engine: OPTI 225
Join Date: Aug 2002
Posts: 417
It sounds like a misfire with the engine to me.... and the high grade fuel is just 'covering up ' the problem....

From memory , it thing that engine is CDI ignition. so , proably no fault there, Have you changed the plugs ???? Can you change the plug leads....

If the plug leads are expencive , you can wrap insulation tape around them to see if this solves the problem... if it does , then change them
__________________
NOT THE SHARPEST KNIFE IN THE DRAWER
TIM is offline   Reply With Quote
Old 26 September 2004, 07:39   #6
Member
 
Country: Norway
Town: lillestrøm
Make: bombard 550
Length: 5m +
Engine: yamaha O.B. 75
Join Date: Sep 2004
Posts: 22
When i bought the boat 3 years ago it was just serviced, and some of the problems (misfire) accured 1/2 year afted that when the water temp was as high as 22 d. C (not often in Norway), the other "problems" (low power) are present at all temperatures.
I´m gonna do a full tuning soon, i guess any wrong timing will show up then.
I have a problem accepting that there are other serious problem with the motor, for eg. last winter i had my boat under a plastic wrapping and it was left outside with only new gear oil and some alcohol on the tank, then in april revealed after loads of snow and temperatures below -25 d. C.
At the third pull it started and ran like a dream.

Thank you for all answers

Pellesmil
__________________
pellesmil is offline   Reply With Quote
Old 26 September 2004, 13:46   #7
Member
 
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Make: BLANK
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
In the UK the most common fuel is unleaded 95 octane. 97 octane lead replacement is still around and super unleaded is 98 octane but stupidly expensive - then again ALL our petrol is stupidly expensive - 1.21 EU per litre for normal unleaded - 98 octane is about 15 eu more!!!

Although not many people realise it 97 octane proper leaded petrol is not banned but it is a very restricted supply.

The higher the octane rating the better usually but an engine has to be set up for it.

During the war Spitfires used 150 octane!!!
__________________
codprawn is offline   Reply With Quote
Old 29 September 2004, 15:02   #8
Member
 
Country: Norway
Town: lillestrøm
Make: bombard 550
Length: 5m +
Engine: yamaha O.B. 75
Join Date: Sep 2004
Posts: 22
Back again after a tune up on my sweet 75 hp, ignition is suposed to be 2 deg. ATDC on idle and 22 deg. BTDC on full advanced.
The engine was quite ok at idle, around TDC adjusted it back to 2 deg. ATDC, at full advanced it was correct.
This could be the reason for the cickback, but maby i have to live with some of that, i guess it is not normal to have a 75hp as manual start.
Soon i´m gonna replace the sparkplug leads, just in case, and thru the fall i will be doing some tests on eqonomy vs. efficiency in the octane field.
Be prepared for some stunning resultes from Pellesmil´s nautcal test laoratories.
Have fun and ride the wave.

Pellesmil
__________________

__________________
pellesmil is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 23:37.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.