Favorite Premix Oil and Ratio

Discussion in '2 smokers' started by craydds, Mar 26, 2013.

  1. dancy

    dancy Undescended Testicle

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    Yes it is made for the injection system but many vintage racers I know premix it. I don't think it says not to anywhere, just flows better and more consistently through the pump.
    #41
  2. Twin-shocker

    Twin-shocker Long timer

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    Gordon Jennings testing on 2T oils is nearly 40 years out of date and bears little relevance to 2013. Contrary to popular belief most modern 2T "fully synthetic" oils are anything but, and have low smoke additives, which are generally thinned down with up to 20% kerosene. This leads to a very thin oil also suitable for use in 2T injection systems, but far from ideal for use in off road bikes, which may be used infrequently as the very thin oil provides little long term corrosion protection.

    Using more oil than is required in low heat motors (trials, enduro, fun bikes) will quickly result in badly clogged exhaust systems, and excessive carbon build up in exhaust ports. All 2T motors tend to put about 25% of the intake charge straight out through the exhaust port, if you running 50% more oil than it required the end result of this is pretty obvious!

    Too much oil tends to weaken the air-fuel mixture, and to compensate less than optimum carburetion settings are required, which will reduce power and make motors feel dead and unresponsive. Modern fully synthetic oils work very well indeed, and there are even specially developed oils which will greatly help with getting accurate plug colour readings if you chose to use modern E fuels, rather than specific race types.

    10 years or more ago the idea of castor/synthetic hybrid oils was state of the art, but today pushing this is little more than a marketing scam, as advances in full synthetic technology mean modern full synthetic oils are superior to the hybrids, and far more suitable for serious competition use as varnish build up on internal parts is eliminated entirely, and if something like Castrol XR77 is used, its also far easier to get accurate plug readings if you are using pump fuel.
    #42
  3. CharlieT

    CharlieT old school

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    Well, goes to point out what I had said, before you can give an answer, you need to know how the motor is going to be run, etc. I beleive this gentleman was referring to an air-cooled mid-70's YZ400, an off-road racing bike that doesn't have oil injection. No if he is going to put around on it, no he doesn't need the 20:1 most likely. In fact any pre-mix ratio is going to be wrong for a given engine as it goes thru the rpm range. In a common case scenario, it will be too rich on oil at idle, low rpm, maybe about right at mid-rpm, and lean at high rpm. Its why a very common place for racers to stick their motors is near the end of the tracks longest straight, after they have been at sustained high rpm. Its not so much their jetting is off, but that their pre-mix ratio is off.

    THe point about not providing any corrosion resistance with the new thin oils, to me reinforces my comments about using the castor blend for the purpose of providing better lasting lubrication to the lower end.....*under race conditions*. See my comments on contact time and look at the Maxima link on oil deposition. THe modern synthetics simply to not provide a a lasting film of lubrication in the lower end that is spending most of its time around 10K rpm and above.

    As for 25% of the intake charge going out the exhaust, you are indeed correct. However if you are doing nothing to recover that lost fuel charge, then you are wasting tons of potential power and you have a piss-poor designed exhaust, one that is designed for safety, not performance. One of the primary purposes of tuned expansion chambers is to recover that lost intake charge. The timing of the return wave coming back from the convergent cone is intended to reduce the amount of unburned fuel going out the pipe and to force it back into the cylinder, kind of a crude, but effective supercharging effect. It is possible to recover most of that 25% with the right pipe or to even go to far. Besides the shape of the pipes cones, header length also plays a part. Too short of a header length and you not only recover the unburned fuel, but you can also force burned gases back into the cylinder, reuslting in over heating and subsequent loss of lubrication on the exhaust side of the piston resulting a a stick.

    COuld you explain a little bit more about your comment "Too much oil tends to weaken the air-fuel mixture". A little more detail on that would be appreciated.
    #43
  4. Twin-shocker

    Twin-shocker Long timer

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    If you choose to use injector type "fully synthetic" 2T oils, rather than proper pre-mix only race oils, in competition machinery then the very thin oil injector oil, may well lead to corrosion damage in some cases. However genuine full synthetic PRE MIX ONLY oils, all provide excellent corrosion protection, and some such as Castrol XR77 have been specifically developed to help with providing accurate plug colour readings when alcohol bearing fuels are being used.


    In terms of fuel/oil ratio, serious road racers riding 2T bikes, very often vary the ratio for different tracks, using more oil on tracks with extended periods of WO running, to help with heat dissipation, and less oil on tracks with more twists and turns, as this tends to improve throttle response. Most play bike riders make the mistake of using far too much oil, and if a rider chooses to use more oil than is really required, its best to use a good quality semi synthetic or mineral type oil, for the simple reason these burn much more easily than full synthetics, and less will find its way into the exhaust port and exhaust system.

    Not many people are in a position to be able to design and manufacture an expansion chamber that works properly for their particular bike, and many 2t bikes dont have expansion type systems anyway, so 25% of the intake charge making its way out of the exhaust port on every revolution of the crank is an unfortunate fact of life on almost every production bike. This means that there is certainly a need to either use the correct type and amount of 2T oil, or to get used to servicing exhaust system parts much more regularly than really required, or to simply put up with a bike that may not run all that well.

    Overly oily fuel mixtures are higher in viscosity than those using less oil, which means carbs need to be set up with this in mind, as the higher viscosity fuel requires bigger jets to achieve the same fuel flow which would be the case if the correct amount of oil was being used. Less fuel flow tends to weaken the air/fuel mixture, and in combination with more oily mixtures not burning as easily as those with less oil, leads to reduced levels of power, and dead, flat feeling motors.
    #44
  5. Tim McKittrick

    Tim McKittrick Long timer

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    [/QUOTE] Overly oily fuel mixtures are higher in viscosity than those using less oil, which means carbs need to be set up with this in mind, as the higher viscosity fuel requires bigger jets to achieve the same fuel flow which would be the case if the correct amount of oil was being used. Less fuel flow tends to weaken the air/fuel mixture, and in combination with more oily mixtures not burning as easily as those with less oil, leads to reduced levels of power, and dead, flat feeling motors.[/QUOTE]



    It's probably been mentioned before but it bears repeating: more oil in your mix means there is less fuel per volume of measure and this means your carburation trends lean. Thus a 20:1 mix is going to be leaner than a 50:1 ratio. As to the degree of the leaning effect of viscosity I can't say, but both result in the same tuning considerations needing to be made.
    #45
  6. Scootern29

    Scootern29 Long timer

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    This thread is starting to deliver. :1drink
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  7. Valleyrider

    Valleyrider I Survived The '60s

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    I run Blendzall (castor) at 32:1 mixed with non-Ethanol premium.
    Never use it in the bike after 24 hours.
    Gasoline destroys the lubricating qualities of bean oil.
    Old gas goes in the lawnmower.
    It makes mowing the lawn a sort of non-racing pleasure
    #47
  8. anotherguy

    anotherguy Long timer

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    So then. What do you run and at what ratio?
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  9. CharlieT

    CharlieT old school

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    Looking back on this thread,I guess I need to take some of my own advice....what engine, what rpm, how is it being used. I tend to think in terms of of full tilt, built to the ragged edge race motors. One's that may be getting their jetting adjusted from early morning practice to late morning practice and again to afternoon race time. Engines that get a fresh set of rings after each race weekend, a complete top end after every two-three weekends and a lower end rebuild about every 4-6 weekends. Engines that if they drop only a couple of hp it can mean the difference in a podium or not.

    I would be interested in reading more on this claimed effect of viscosity on fuel flow. Got any links to any articles. Familiar with the %oil:air/fuel affecting jetting, but have never heard of this viscosity having any kind of significant effect on jetting.

    As for fule flow thru the jets, IIMHO, other factors play a much more important role in the efficiency of flow and atomization of the fuel charge. The most signifcant being the old volume versus velocity debate. Most carbs operate off of Bernoulli's principle and are designed to offer maximum flow and optimal atomization at a certain velocity of air flow over the jet orifice. Folks tend to think that going to a larger carb will mean more fuel and more power. Quite often its the opposite that is true. The larger venturi carb may make more power at near max rpm where the velocity is sufficient, however at low-mid-range rpm the velocity is not sufficient for the carb to flow fuel and properly atomize the mixture. Most riders spend much more time in the mid-range, where a smaller diameter carb will likely improve perfomance as the smaller carb increase the velocity, improves the fuel flow thru the jet and improves the atomization of the fuel. WIth the larger carb, they think they are burning more fuel and making more power beacuse they had to go to a larger size main, where in reality, they had to go to a large size main because the lower velocity results in a less efficient flow of fuel and the larger main was needed to compensate for that decreased efficiency.

    Pipes, you are right, like i said most are built for safety. Companies don't want the average Joe rider to go out and repeatedly stick his motor. They are at best compromises between safety and performance. Kinda of off subject, but wasn't there an aftermarket pipe builder that sold a kit with varying length spacers to place between the pipe and the cylinder to offer more tuning.

    Like pipes, carbs are typically jetted for safety and are on the rich side. Beside too much fuel, there can also be too much oil. Too much fuel cools the temperature, which then results in a less efficent burn. Then the oil, which there is too much of do to the rich condition, burns much slower than the air/fuel mix and gets deposited as a black damp crust on the piston, gums up a ring, and becomes the dreaded spooge throughout the exhaust system. So the average rider decides there is way to much oil in the premix and dramatically rduces his ratio to cut down on the spooge. THen he goes out and pins it on a long straight and sticks it. He applied the wwrong solution to the problem. The proper solution would have been to correct the jetting.


    Got to get back to work here, but interesting thread and it goes to show that there is no simple answer to the age old question of what oil and ratio do you run!
    #49
  10. Twin-shocker

    Twin-shocker Long timer

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    Most people dont ride bikes with highly strung race motors, so its a big mistake posting up things that apply to a very few riders, who if they are serious racers will know exactly what oil ratio to use and why anyway.

    In the main more problems are caused by using too much oil, than too little, and the spurious stuff related to testing carried out nearly 40 years ago, is still being brought up to support using excessive amounts of oil.

    Main things to remember when it comes to 2T oils, is to use an oil to suit your application (full synthetic pre-mix only is perhaps the best for any sort of competition bike), and a mix ratio to suit the use you will be putting your bike to.

    Motors which run at high rpm for extended periods of time, and generate plenty of heat, obviously need more oil than low rpm low heat motors.

    I suggest anyone reading this thread who is running a low heat 2T motor on 50:1 or greater mix ratio, should get some fully synthetic PRE MIX ONLY 2T oil, and see how much better their bike will run on 70:1 mix. It really does make a big difference, especially so if exhaust duct is properly cleaned out before starting to use less oil.
    #50
  11. CharlieT

    CharlieT old school

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    Just as most do not run hi-strung motors, most also do not run low heat trials bikes either. SO perhaps it is a big mistake to post up thigns that only apply to trials bikes.

    Lets see what the average rider will experience.

    Too much oil:
    1. fouled plugs
    2. gummed up, stuck rings causing low compression
    3. gummed up, malfunctioning power valves, if so equiped
    4. the dreaded exhaust spooge
    5. splattered oil stains on the back of their $100 riding jersey.

    Too little oil:
    1. Piston seizure
    2. Cylinder wall damage sufficient to require possible boring or replating of nikasil, etc
    3. Lower rod bearing seizure

    Boy, I think I'll stop there as it is obvious you are correct, spooge and fouled plugs are much more serious problems

    Jennings writings are from the late '70s, but their is plenty of supporting documentation out there that is from within the last 5-10 years, or newer. But hey, at least these folks are looking for and providing supporting documentation, unlike others. Oh, that reminds me, where is the supporting documentation that I politely asked for regarding mix ratio affecting fuel flow thru the jets.

    Seems we have heard that before. Few folks reading this thread run the hi-strung road race engines or the low rpm trials bikes. So most will likely end up with a premix ratio somewhere between my road race 16/20:1 and your trials 70/100:1.

    Hopefully they will take into consideration a number of factors discussed in this thread and make an informed decision on what they feel comfortable with.
    #51
  12. Twin-shocker

    Twin-shocker Long timer

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    Other than reduced performance, and dull dead feeling motors, there is nothing negative about using excessive amounts of 2T oil, at the same mix ratios popular 40 years ago.

    However using the correct oil at the right mix ratio is a win win situation, as this will improve performance as well as drastically reducing maintenance requirements.
    #52
  13. CharlieT

    CharlieT old school

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    SO, if we get back into road racing, I should run your 70+:1 oil mix?
    DO you have stock in Wiseco or sell Amsoil, btw??
    #53
  14. Twin-shocker

    Twin-shocker Long timer

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    The oil used is very important (notwithstanding ridiculous advertising blurb), and mix ratios need to be adjusted to exactly suit specific use.

    For serious road racers who need to adjust carburetion for specific tracks and atmospheric conditions, using the correct oil is even more important, as modern fuels make taking plug readings very difficult, unless oils developed to help provide accurate readings are being used.

    However I would imagine as most serious 2T road racers will already have a pretty accurate understanding of lubrication matters, they wont need to ask questions on forums like this one.
    #54
  15. CharlieT

    CharlieT old school

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    So we have discovered one thing here, our Mr. Know-it-all expert doesn't know the definition of sarcasm.
    #55
  16. joexr

    joexr Banned

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    I cant document it either , but 30+ years ago I was removing the oil injection from an RD and was told by a few different mechanics about increasing jet sizes to compensate for the oil increasing the fuel viscosity. Believe they were telling me about 5% increase.
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  17. dancy

    dancy Undescended Testicle

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    :lol3

    Fookin' n00bs
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  18. CharlieT

    CharlieT old school

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    Now that I could believe, as you are going from an oil injection system in which there is only straight fuel going thru the jets to a premix in which there is a fuel oil mix. But changing from say 32:1 to 40:1 altering the fuel flow thru the jet...well I would like to see some supporting documentation.
    #58
  19. joexr

    joexr Banned

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    Well , thats a 20 or 25% difference , depending on which way you look at it.
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  20. CharlieT

    CharlieT old school

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    SOrry, but you are talking apples and oranges here. You are referring to the change in oil added to the premix as a %. What we were talking about is the change in ratio affecting the fuel flow through a jet.

    That and while it may be a 20-25% change in the volume of oil using your comment, in terms of oil to gas mix in terms of percent, it's less than 1% change. 32:1 premix contains 3.13% oil. A 40:1 premix contains 2.50% oil. So in terms of the amount of oil present in the volume of fuel, it is only a change of 0.63%

    Hope that make sense.
    #60