modern unleaded fuel v. old petrol engine designs.

Discussion in 'Help Wanted' started by pp-admin, May 29, 2016.

  1. pp-admin

    pp-admin Member

    this an old debate and i remember not really coming to a solution years ago when unleaded petrol became available and the
    2,3,4,5 and 6 star fuel (!!!) disappeared from the forecourts along with all the lead in it. add to this dilema that modern petrol contains bio fuels and is not 100% mineral content.

    my tech question to you clever chaps is what is the real harm done to old sidevale engines (30+ years old) in using modern fuel as the choice at the petrol pump is either standard unleaded or super unleaded, plus possibly the opportunity to dose into the fuel tank some kind of ad-mixture aimed at replacing the lead.

    I remember reading all kinds of horror stories about the dangers of using modern petrol in old technology engines but really, does it matter. I have a almost brand new 40 year old honda generator with the famous G300 side valve engine which is a late 1960's design, If i simply buy standard unleaded and start using this generator for long running periods, what will the modern petrol do to the old engine ???

    i recall the subject of having hardened steel valve seat inserts fitted as a solution (at great cost !!) as well as manufacturers selling all kinds of snake oil ad mixtures to substitute the missing lead.....absent lead may not be the only problem in using modern petrol in old engines ??

    would be nice to have some expert guidance from you gents and lay this problem to bed finally. i guess the same dilemma also faces any of us engine men who have very very old petol stationary engines in our collections. My oldest is from 1911 !!!

  2. campingstoveman

    campingstoveman Active Member

    Petrol originally didnt have lead in it so our engines are safe, lead came into use in the 60s/70s and the chemicals are unlikly to harm our engines unless they have brass parts or other alloys or rubber materials and we dont keep petrol in them permanently.

    Martin P
  3. robtheplumb

    robtheplumb Member

    I find most of my engines run rough on this newfangled unleaded fuel, they all tend to misfire now and then so to cure this I run a 25:1 mix with kero. Any more than that then they are a pig to start.
  4. campingstoveman

    campingstoveman Active Member

    I don't have trouble with the fuel in my engines but if I do have rough erratic running the problem seems to go away when I have its magneto serviced or rebuilt.

    My Lister Hamworthy set ran last Sunday without missing a beat, the best its done since I bought it, the reason a rewound rebuilt magneto.

    Martin P
  5. petternut

    petternut Administrator

    When our engines were designed the general petrol was 78-80 octane so a calculated dilution to about that level is probably a good idea.


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