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What octane to use

Discussion in 'Mechanic and Repair' started by emtfire148186, May 26, 2010.

  1. emtfire148186

    emtfire148186 LawnSite Member
    Messages: 62

    I have 2 scag walk behinds that i use 89 in. Is this ok or should i use 91?

    I use 91 in all my 2 stroke engines
  2. punt66

    punt66 LawnSite Fanatic
    Messages: 8,536

    i use 87 in everything. No issues. If its not detonating then your just wasting your money.
  3. emtfire148186

    emtfire148186 LawnSite Member
    Messages: 62

    OK thanks....I'll stick with what i use now
  4. clean_cut

    clean_cut LawnSite Bronze Member
    Messages: 1,327

    To my knowledge, you only need the 89 or higher in 4 mix equipment, such as some stihl blowers and trimmers.
  5. emtfire148186

    emtfire148186 LawnSite Member
    Messages: 62

    Ok great...Thanks for the info
  6. johnwon

    johnwon LawnSite Senior Member
    Messages: 299

    From what I've read, if your engine is factory set or tuned to, lets say 87 octane, then using higher octane will have the same effect as slightly retarding the timing. The higher the octane the more resistant it is to pre ignition. So in theory the position of the crank maybe just a little past the optimum position when the explosion takes place in the combustion chamber.
  7. emtfire148186

    emtfire148186 LawnSite Member
    Messages: 62

    ok thanks for the info. I was told to use 91 before, but i wasn't sure about it. I been having problems with my walk behind backfiring. I was told that it would sometimes fire on only 1 cylinder. I did everything possible to try and fix it. tune up, coils, new gas, adjusted valves, cleaned carb about 5 times really good, compression is like 130-135 on both sides. the small engine mechanics cant find anything wrong. My buddy said switch to 91 or 93 to help clean it out. Just wanted everyone's opinion

    STIHL GUY LawnSite Fanatic
    from CT
    Messages: 5,226

    i use 87 in the truck and mower and 91 in the 2 stroke stuff and the br600
  9. ajslands

    ajslands LawnSite Silver Member
    Messages: 2,238

    I use diesel! But in my mowers I use 87
    Posted via Mobile Device
  10. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    How many grades y'all got out that way?

    Around here it's 87, 89 and 93...

    These are carbureted engines, no computer.

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