I have been using Amaco high octane, i see that some users are switching to the lowere octane. What is the reasoning for this? I'm currently running a 95 pro 150 Yamaha. Any sugesstions?
Finadict, stick with the recommended fuel for your engine,regardless. Some do reccommend the highest octane, but most do not.<br />87 octane is the normal reccommendation, but I don't know what yours is. Anything over that is a waste, and can actually cause cylinders to run too cool or hot,or foul plugs or...You get the picture, Im sure. I would ask your local Yammy dealer,or if you have the opeator's manual,check there.
Ditto 12 Footer. Use what the manual says. High octane can run too cool and turn your engine into an octane junkie.<br /><br />Too cool combustion temps.=carbon buildup.<br /><br />Same rules apply for ANY four stroke.
I'm with 12Footer.<br /><br />I never ran onto a 2 stroke, other than racing engines, that needed premium fuel (and the racing engines usually wanted methanol with lots of nitro and castor oil).<br /><br />For many years outboard manufacturers recommended "white" gas, specially formulated for marine/aviation uses. It was lead and additive free and about 80 octane. You can buy it today at about a bazillion bux a gallon for Coleman lanterns and stoves.<br /><br />I don't know of a manufacturer that currently recommends octane higher than 87.<br /><br />If I am wrong, of course, go with what your MFG says.<br /><br />Red sky at night. . .<br />JB
WHITE GAS DO'S NOT HAVE LEAD IN IT IF<br />IT DID THE ORFACE WOULD NOT LAST LONG.<br />REMEMBER WHEN THEY SAID IT WAS OK TO<br />USE UNLEAD IN THE LANTERNS.<br />THAT WAS THE REASON.<br />REX A.
Some of you guys just threw me for a loop! I agree to use the Min. Octane fuel required. I want to know how HIGHER octane can cause engines to run "cooler,hotter, or foul the plugs"?????<br /><br />You use to low a octane you will get preignition and/or detonation. <br /><br /> So are you saying?? If you cannot get; lets say (mid-grade fuel) to go to the lower octane because you dont want to run your engine "cooler,hotter, or foul the plugs"????
Octane rating is the fuels ability to resist pre-ignition. In a sense, the higher the octane rating the less likely the fuel is to explode in the combustion chamber rather than poof! You want a CONTROLLED explosion in the combustion chamber.<br /><br />Higher octane fuels reduce combustion temperatures. In doing this, they are more likely to leave deposits. These deposits become super heated (glow) and set off the new fuel charge before the plug fires-thus pre ignition or spark knock. That phenomonon causes the pistons to pit leading eventually to engine failure.<br /><br />Keep your engine decarbonized and use the grade of fuel recommended by the manufacturer.
Hi, Trent. If you get knocking or detonation when using the recommended octane, the problem is not the fuel. It is ignition timing or excess deposits (carbon) in the combustion chamber.<br /><br />A Thermodynamicist explained it all to me once. It was all Greek to me except the bottom line: The manufacturer calibrates the fuel system and specifies ignition timing for a given octane and compression ratio. Going below that risks preignition, going above produces different combustion dynamics than they intended which may cause other problems.<br /><br />Use what they designed the engine for.<br /><br />Red sky at night. . .<br />JB
Hello,<br />If it makes anyone feel better, the owners manual for my 96' Evinrude 15 Hp states the minimum octane to be used is 67! Where in the world would you get anything below 80 in the US? <br />Good Luck,<br />Little Bear
I just looked at my engine manual, "Use any regular unleaded,regular leaded, or premium unleaded automotive gasoline" Do not exceed 10%ethanol by vol.Min. octane 87. In addition you must use NMMA certified TC-W3 oil.<br />I have always used Texaco Premium,because that's all the marina's sell in this area, and never had a problem. My$5 worth.
Thanks for all the replys, I'm not sure which octane to use. I don't have the manual. I have no problem buying premium, That all I've ever used. But I have noticed that my plugs have always been wet. My compression is good, my carbs have been overhauled and adjusted , engine decarbed and tuned, but they still come out black and wet. The dealer advised to stay w/ the recommened plug and NOT go to a hotter one. I was wondering if the high octane is what is causing my plug problem. I'm currently running a 95 Yamaha Pro 150. Any sugesstions?
Thanks for the replys.. <br /><br />Im pretty familiar with octane and ratings. Djohns you have it backwards..Octane is fuels resistance to "Knock" not pre-ignition. <br /><br />Anyway here is a pretty good article.web page
Boy you're right it's a dry read. Sect. 6.2 describes a knock as "ignition arriving before the flame front." Thus pre ignition, whatever set it off. Just a difference in terms for same phenomonon. Anyway, it's NOT good.
Yeah. djohns, I guess I never understood what the big deal was about the difference between detonation and pre-ignition....the way I look at it, they are twin sisters that travel together....when one shows up, the other isn't far behind.........and the carnage looks the same!
you should get a owners manual but if plugs are wet reduce to middle grade is that a v max I dont think you need the highest octane thats off the top of my head I run a yammy 115 v 4 its gonna start getting 87 Ive been running the middle but my plugs are wet too the right octane ,mix should increase power a tad also
fin addict,<br />Great question. This one has been asked in the past. EVERYONE PLEASE NOTICE: We have several search links above. We have had many incredible discussions about almost every conceivable engine and motor topic now on these boards. PLEASE, give our keyword search a try before posting and you'll be surprised what information you just might find is already posted.<br /><br />I did a search with the term octane. Please read some of the threads I link to below because they go even further in-depth than this one does.<br /><br />Topic: Correct Octane<br />Topic: What octane<br />Topic: To all wondering about what type of gas <br /><br />Thanks to JB, 12Footer, ODDD1, Dhadley and the rest of all of you for answering so many of the same questions multiple times. Please also encourage people to use the search feature when you remember good posts from the past that apply. fin addict, thanks for giving me the opportunity to spout.
