Fuel Mixture What would happen if you constantly ran your engine rich like at break in ratio?

Discussion in '2-Stroke Engines' started by DeathProof, Apr 28, 2012.

  1. DeathProof

    DeathProof Member

    if you constantly ran it rich at break in ratio 24:1 instead of lean after 2 tanks 40-50:1 what would happen? if it runs awesome at break in stage whats the difference just leaving it?

  2. Fabian

    Fabian Well-Known Member

    Nothing would happen, if the carburettor is jetted correctly.

    Because of the loads i tow and virtually 100% duty cycle placed on the engine, i run a 20:1 oil fuel ratio and have been doing so since the word go, about 2 years ago.

    """ALL""" my engines have had a consistent problem with bottom end bearing failure, but this was largely attributed to the standard CDI giving an ever increasing spark advance with rpm.
    Since fitting the Jaguar CDI, i have not had any more big end bearing failures; in my case, the only reason why all 7 engines failed.

    From what i understand the newer engines use a crowded roller bearing setup for the big end which is significantly more reliable than the previous caged needle roller bearing.
    professor likes this.
  3. ddesens

    ddesens Member

    I don't think you would have a problem. You might have to go through spark plugs a little quicker. You might have more smoke out the exhaust than most. You will definitely have more oil dripping/spraying out your exhaust.
  4. Fabian

    Fabian Well-Known Member

    Oh yes, there "will", make that """WILL""" be more oil dripping/spraying out the exhaust and more oil on the operator and more oil on the mechanicals.
    As the cooling system on these engines is fixed i.e. pegged to the surface area available for heat transfer, the only other method of heat extraction is through thermal transfer to unburnt excess oil, hence when riding in shorts, your legs will get attacked by scalding droplets of hot oil and socks, shoes and jeans will essentially become a dirty rag.

    20:1 isn't necessary if the engine is lightly loaded; rarely seeing high duty cycle i.e. putt, putting around.
    In such a scenario, you could easily get away with 40:1, even 50:1 if gently cruising about, using cheap 2-stroke mineral oil.

    My situation though is perfectly suited to cheap 2-stroke oil because i'm using it for heat extraction, not for any extra lubrication.
    Last edited: Apr 29, 2012
  5. DeathProof

    DeathProof Member

    thanks guys i appreciate the feed back! :smile:
  6. tooljunkie

    tooljunkie Member

    the only thing i would add is the soot from the rich mixture may clog the screen in the exhaust,it does it on chainsaws and trimmers,so i would expect to clean or replace the muffler from time to time.
    this is especially true if synthetics intended for leaner ratios (optimol) are mixed rich.
  7. Fabian

    Fabian Well-Known Member

    @ tooljunkie

    I would have thought the same thing about the muffler clogging up at 20:1 but in two and a bit years, i've never had the need to clean it out, though my engine mostly runs at 100% duty cycle.
  8. Cavi Mike

    Cavi Mike Member

    Fouls the plug constantly and leaves a puddle of oil under your exhaust. I keep mine rich because I'm more concerned with longevity than performance.
  9. andrew5826

    andrew5826 New Member

    On my goped motors I mix 91 octane with redline at 32:1, heat cycle it for 10 mins not letting it idle too much and just let it rip wot most of the time. All my motors look brand new inside and are hitting 14.5k+. The reason you run the motor hard is so that more pressure gets behind the piston ring and seats it better thus more power.
  10. LaLongueCarabine

    LaLongueCarabine New Member

    Wow, that's what I remember we used to do with our 125-175cc back in the day.
    We never had a problem with these engines and we ran them hard.
    Does it even make sense to go with the super lean mixes that some say are OK?
  11. Fabian

    Fabian Well-Known Member

    From all the research i've done on this subject it comes down to three simple aspects of oil.

    1) Lubrication
    2) Heat extraction, broken down into two components for a 2-stroke engine.
    3) Blow-by prevention

    Of the first two aspects, the engine only needs as much oil as is required for adequate lubrication to prevent engine damage, and only as much oil as is required to transfer heat from internal (moving) parts to the main body of the engine.

    The other less considered aspect of oil ratio in a 2-stroke air cooled engine is secondary heat extraction.
    The greater the oil ratio, the greater the removal of engine heat over and above the cooling surface area of the engine.
    If under a high duty cycle, the engine can be kept within safe operating limits by adjusting oil ratio (whilst keeping air/fuel ratio within safe levels), should cooling air flow become insufficient.

    The third as often misunderstood effect of oil ratio is the barrier effect, whereby cylinder distortion due to uneven cooling creates (localised) low piston ring to cylinder wall integrity, allowing blow-by.
    A higher oil ratio in such circumstances becomes a gas barrier between piston ring and cylinder wall; reducing pressurized gas from passing by the piston rings.
    Suzuki did a bunch of research on this problem back in the early 1970's and found contrary to popular belief that higher oil ratios gave more power, even though increased oil reduced fuel octane numbers.
    The extra power was coming from reduced blow-by.

    This information was so reviled by the 100:1 spooks on a particular forum that i was subsequently banned after continually backing up the concept with irrefutable data.
    Naturally, in a water cooled engine with excellent metallurgy, oil ratios can be drastically reduced as bore distortion is kept within very tight tolerances.
    Unfortunately excellent metallurgy and a low cost bicycle engine don't exist in the same space.
    That doesn't mean to say you can't use 100:1 oil/fuel ratio in a lightly loaded situation with overly rich jetting.
    It just means you can't use 100:1 oil/fuel ratio in China Girl engines with optimal jetting at high duty cycle and next to non existent air flow over the engine, such as full throttle hill climbing at 5 miles an hour at 5,000 rpm on a 100 degree day for an extended period of time.
    Last edited: May 3, 2012
  12. andrew5826

    andrew5826 New Member

    i would never go leaner than 32:1. oil ratio doesnt really make too much of a difference. tuning the low and high speed jets do
  13. 2stroker

    2stroker Banned

    Just dont let gas sit in the carb. It will gunk up quicker and you will be cleaning it sooner. Besides that your good. It will have plenty of lubrication!! Keep your plugs clean!
  14. DeathProof

    DeathProof Member

    2 stroker was brief and straight to the point lol he makes sense no technical :poop: