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Fuel:Oil ratio in an RM80

  • 25-08-2009 12:07am
    #1
    Interceptor
    Registered Users, Registered Users 2 Posts: 3,180 ✭✭✭


    I have an old 1988 Suzuki RM80 scrambler out in the shed - it came needing some work and I have finished most of it. I want to start it but the tank is dry, it runs on premix and I'm not sure of the right oil mix. All the Googling in the world hasn't helped - anyone have one and have the right answer (or a manual in .pdf)?

    No guesses thanks - I don't care enough about it to be fitting new pistons so I'll just start with 25:1 and see if it fouls the plug at that...

    Thx,

    'cptr


Comments

  • #2
    KamiKazi
    Banned (with Prison Access) Posts: 6,201 ✭✭✭KamiKazi


    Sorry mate, don't know.

    'kkzi


  • #3
    zzr
    Closed Accounts Posts: 88 ✭✭zzr


    ya could go with the outboard motor mix which is 50:1 oh and do you think an rm would look to gay:cool:


  • #4
    KTRIC
    Closed Accounts Posts: 9,463 ✭✭✭KTRIC


    Is this you 'cptr ?? Looks a bit gay to me.

    1989_RM80K_Rob1_560.jpg


  • #5
    Pique
    Registered Users, Registered Users 2 Posts: 3,052 ✭✭✭Pique


    Bruce Grobbelaar's really let himself go....


  • #6
    Interceptor
    Registered Users, Registered Users 2 Posts: 3,180 ✭✭✭Interceptor


    LOLZ... You must have been trawling www.homobikerpicz.com for ages looking for that! His RM is much cleaner than mine but his purple shorts and Mickey t-shirt clash really badly with it...

    'c


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  • #7
    Steffano2002
    Registered Users, Registered Users 2 Posts: 5,918 ✭✭✭Steffano2002


    Browsed a few french forums and it seems the RM85 of 2002 takes 2.5% or 3%... Don't know if it's any help...

    Yeah I think you should start at 25:1 (4%) and see how the spark plug looks after a few hours...


  • #8
    CJhaughey
    Registered Users, Registered Users 2 Posts: 14,907 ✭✭✭✭CJhaughey


    25:1 is too much oil in the mix, you will constant;y foul plugs at that ratio.
    Use high quality full synthetic oil and mix it at 40:1 and you will be fine.
    Racers used to use 32:1 in the old days with poorer quality oils but thats race use which I doubt you will be subjecting the RM too:)
    I have been riding premix 2 strokes for years and this has never failed me in my RMX 250 which I run at 40:1 premix.
    Castrol TTS is full synthetic as is the Rock oil in the gold bottle.

    Running too much oil actually gives you a lean condition combustion.


  • #9
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,790 ✭✭✭✭galwaytt


    Interceptor wrote: »
    ......No guesses thanks - I don't care enough about it to be fitting new pistons so I'll just start with 25:1 and see if it fouls the plug at that...

    Thx,

    'cptr

    ...25:1 is exactly that: guessing. Contrary to popular opinion, over-oiling increases the chance of running lean, and seizing............2% is perfectly safe. You're using 4%. Way, way too much.

    The reason over-oiling causes problems is simple. On an intake stroke, the cylinder will take in, lets say, 100cc. Ordinarily, this is made of an air:fuel mixture ratio in or around 14.8:1. These volumes are fixed by the size of the cylinder, and the design of the ports/engine. The fuel mixture itself, is what you're looking at, and is made up of 98% petrol and 2% oil. Now, if you change the amount of oil in the fuel mixture on the intake stroke to the cylinder, by increasing the amount of oil in the mixture itself, and the total amount taken in is constant (which it is, your 100cc, say...), then something has to be less. In which case, it's your petrol. Less petrol in a given volume of air to the cylinder, is.............yep LEAN !!. Want to guess what happens to two-strokes that run lean...........I think you know already !!

    Probably one of the few cases where too much oil is a bad thing.

    50:1, 2%, 20ml in a litre, 50ml in 2.5litre, 100ml in 5 litres.........whichever is the easiest for you.

    So endeth the lesson. :)

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • #10
    Interceptor
    Registered Users, Registered Users 2 Posts: 3,180 ✭✭✭Interceptor


    galwaytt wrote: »
    So endeth the lesson. :)

    Muchos gracias! (Take my RM on a trade-in for your DT???...:p)

    'c


  • #11
    Steffano2002
    Registered Users, Registered Users 2 Posts: 5,918 ✭✭✭Steffano2002


    galwaytt wrote: »
    50:1, 2%, 20ml in a litre, 50ml in 2.5litre, 100ml in 5 litres.........whichever is the easiest for you.
    I disagree (and I know I'm being an@l here...) but:

    2% = 20ml in 980ml, 50ml in 2,450ml, 100ml in 4,900ml

    20ml in a litre, 50ml in 2.5 litres and 100ml in 5 litres = 1.96%

    I told you I was being an@l! :D :P


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  • #12
    CJhaughey
    Registered Users, Registered Users 2 Posts: 14,907 ✭✭✭✭CJhaughey


    I have done a little digging and from what I understand 50:1 is too lean in an 80cc motocrosser, and personally I would not run that lean a mix.
    All available information suggests that 32:1 in an 80cc and 40:1 in a 125-250 is the best ratio as long as high quality synthetic oil is used.
    It will be different for a street tune engine but MX engines are fairly highly tuned as stock and need a slightly higher oil mix.


  • #13
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,790 ✭✭✭✭galwaytt


    My Gas-Gas competition bikes says 1.5% on the tank.........fwiw........so, tbh, in that region and you'll be o.k.

    Oh, and +1 on the quality of oil - that's more important.

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • #14
    CJhaughey
    Registered Users, Registered Users 2 Posts: 14,907 ✭✭✭✭CJhaughey


    What displacement is your Gas-Gas?, I am betting it isn't an 80cc.
    AsI said small displacement engines need more oil, I had a look at the 65cc Gas-gas manual and it recommends 40:1 all the others are 50:1 with full synthetic, probably due to EPA regulations in the US
    Enduro-MX or Trials? Nice bikes BTW.


  • #15
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,790 ✭✭✭✭galwaytt


    CJhaughey wrote: »
    What displacement is your Gas-Gas?, I am betting it isn't an 80cc.
    AsI said small displacement engines need more oil, I had a look at the 65cc Gas-gas manual and it recommends 40:1 all the others are 50:1 with full synthetic, probably due to EPA regulations in the US
    Enduro-MX or Trials? Nice bikes BTW.

    ...250's (a trials, and a Pampera).

    Can't see how engine size affects it. My Partner strimmer runs on the same mix......

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • #16
    CJhaughey
    Registered Users, Registered Users 2 Posts: 14,907 ✭✭✭✭CJhaughey


    Engine size has a lot to do with it, along with the type of use they get.
    Those small displacement engines are revving high to make the kind of power 80cc mx engines make. Remember also that these are watercooled unlike your partners strimmer and as such the tolerances are a lot tighter and less forgiving of mix ratio.
    MX/enduro engines are also different to trials engines because they do so much revving, trials motors (2T) are recommended to be run at ratio up to 100:1, most mix at around 60:1-80:1 this would result in a siezed engine in a MX/Enduro bike in short order.
    I run 40:1 in my strimmer and chainsaws and have never had one sieze on me, in fact I am currently rebuilding a Husky 262xp saw (Crank bearings/seals) with a lot of hours on it and the Piston/rings/bore are in real good shape with the machining lines still visible.
    Trials bike spend a lot of time Idling between stages, granted they get the snot wrung out of them when they go up steep and snotty sections but by and large the throttle isn't pinned to the stop like in a MX heat.

    I hope this explains it a bit better, I run full synthetic 40:1 in all my stuff that need 2T oil and it lasts a long time, you may get more power out of 50:1 and leaner but for me it's just one step closer to the abyss and I have rebuilt too many 2T engines that have been cooked by lean mixes (or no mix) to start changing now.
    That said I have seen almost as many engines damaged by too much oil and the resulting carbon buildup scoring the barrel as it flakes away.
    [URL="http://www.geistware.com/rcmodeling/articles/oil_test
    /index.htm"]This[/URL] page is interesting.


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