Gas Oil Mix Ratio

Discussion in 'Trials' started by aerone, Jul 1, 2010.

  1. neilking

    neilking Been here awhile

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    The oil does not really become a component of the fuel, it is diluted by the fuel. The oil molecules are separated but still retain their original properties and structure, this is by definition a mixture. If it were to become a component of the fuel the fuel and oil would be forming a new compound with a totaly different molecular structure. This would indicate a chemical reaction when the two are put togather or that it has become an azeotropic mixture. In either case it would not have the same properties of either gas or oil but something else, and wouldn't work as intended.
    #21
  2. neilking

    neilking Been here awhile

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    Now, there is heat in the oil molecules, but not as much per volume as gasoline. Since the fuel is a mixture, the oil is displacing some of the volume of gas. Carb jets pass a volume of fuel, a mixture of gas and oil. The stoiosemetric ratio of the fuel is dependent mostly on the gasoline in the mixture since it has a lower flash point, and vaporizes easier, and is the major portion of the fuel. More oil in the mixture means less gasoline molecules in the cylinder at the time of combustion. That doesn't even take into consideration that on the way to the combustion chamber some of the oil molecules adhear to the surfaces that they are supposed to for lubrication(the reason the oil is in there). This takes volume from the fuel. The volume is fixed by jetting.
    #22
  3. darmst6829

    darmst6829 Been here awhile

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    I like this Super Hunky fuel oil article.

    http://jeep.off-road.com/dirtbike/tech/two-stroke-gasoil-ratios-20502.html
    #23
  4. hilslamer

    hilslamer 2XRedheadedstepchild

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    Interesting reading. I thought I would chime into this thread not to argue longevity, fouling or power - but that a 2T trials bike is a pretty unique case of a two-stroke: it gets used largely at low RPM, under very little load, and at small average throttle openings. Not to appeal as the end-all authority, but I;ve been riding trials for 15+ years and the general consensus for oil mix in the AZ clubs has always been 80:1 or higher - not for longevity, not because it was synthetic or castor oil, and certainly not because torque or horsepower advantages mean anything in the unique world of observed trials...

    The oil mix ration becomes similar to what SuperHunky discusses above - enviromental. No, I don't mean to relate that trials bike are evil off-road trenching machines, polluting as they go - I mean the enviroment INSIDE the combustion chamber. IME, if you run a trials bike at 50:1 or richer(oil-rich), the cylinder head, piston crown and exhaust pipe will get very full of carbon very fast. They just aren't designed to scavenge that well, and because they have no expansion chamber etc they don;t run at all that high of an effective compression ration and suffice to say, combustion isn't really all that complete. Carboned-up engine parts are the result, and I can dig up some pictures if you don't believe me.

    Run what you will, but I typicall run good synthetic 2T oil at ~100:1 and have never ever seen a bearing fail or piston seize on any of my many trials bikes.

    :ear
    #24
  5. aerone

    aerone Been here awhile

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    Here is what I have taken away from this so far. It seems the trials bike can use a 50:1 and upwards and a hot rod like the CZ needs a little more lube. I'm going to use one of the better oils and mix up two different one gallon batches and give it a go.

    Should we take a vote?

    For the MAR 100:1
    75:1
    50:1



    For the CZ 60:1
    50:1
    32:1
    #25
  6. Sting32

    Sting32 Trials Evangelist

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    I like what you say, be conservative, Aerone...

    I'd be starting in the bottom of each list, knowing I can tune gas/oil mixtures to the bike & riding... WHen 32:1 smokes too much, as it most likely will even in the CZ, it is wasting the oil and packing your exhaust but it really isnt hurting the bike. The next batch could be 50:1.

    The trials bike should be fine with 50 or so, IMHO scary at 100:1 or above, because there is no extra oil there, or safety factor being built in. if you go trail riding with high gear and high rpms, you could get trouble? I ride with 80-to-90:1 in my bike, hardly smokes at riding temps. But when I go racing down the trail between sections, it smokes the excess oil from WFO operations, but at least I feel it is getting good lube. Nothing makes you feel sicker than the feeling when the oil isnt enough (had the injector line fall off an 80's model yamaha DT once) the engine didnt seize fully because I shut it off as soon as I felt it bog down, but it never did run right after that one.

    I still believe that Air Cooled bikes need more oil in the gas, but that is probably just me. I personally can clean exhaust pipes, and carbon deposites under the heads, & repack mufflers, but I really HATE splitting cases pressing bearings, and sending cylinders to repair shops...

    Your Mileage May Vary...
    #26
  7. buls4evr

    buls4evr No Marks....

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    You already reached the proper conclusion at post #4 aerone.... 50:1 in all your old air cooleds. Set your carb up to use that mix.
    #27
  8. aerone

    aerone Been here awhile

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    I appreciate it y'all. Dumb question: Who (y'all are great) do I properly talk to about my CZ ? I have not found the "vintage motocross" thread yet.
    #28
  9. mung

    mung Been here awhile

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    Have had a 1995 Gas Gas jt 350 since new.It has always run the recommended 128-1 mix since new. The motor has never been apart and it still has enough compression that it takes a manly man to kick it over. What happens is that during slow speed running oil collects in the crankcase then with a burst of high rpm the extra oil gets sucked into the motor providing plenty of lube when you need it.Use 100-1 in my Raga with no problems.
    #29
  10. xtop20A

    xtop20A Banned

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    i always run 32 to 1 ..even when i was competition trials riding my sherpa t 350.i never had an engine failure,kawasaki,bultaco,can-am...another reason to like 32 to 1 is the 4oz. to the gallon.it is an easy measure to remember and estimate::rofl 1/3 of a beer can :1drink
    #30
  11. ragtoplvr

    ragtoplvr Long timer

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    There have been a lot of other changes in newer bikes to help them run at the lower oil content. You should not run an older engine at these lean ratios.

    An old 16 to one or 24 to one engine with sleeve bearings (i know they exist, I have seen one do not know brand) will do best at 24 to one,. If they are roller you can go to 32 to one or maybe 40 to one. I would not ever run an air cooled 2 stroke at more then 40 to one, on hot summer days I would go back to 32 to one. Water cooled can go less oil. The penalty for too much oil is less than the penalty for too little.

    My $.02

    Rod
    #31
  12. Gordo83

    Gordo83 Been here awhile

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    I have seen on this post a couple times about 'jetting the carb to the ratio'. Or 'changing the jetting' for a different ratio.
    How do you figure your jet size for a leaner or richer mixture? And how does the temperature of the day come in to play as far as jetting or mixing?
    I'm running 64:1 and have been doing so for a couple years on my MAR, TY 350 and now a Penton Trials bike. 50/50 Cam2 and 93 Sunoco with Golden Spectro.
    The Penton is a 125 Sachs Iron Barrel. 2nd gear is too high for any trials sections I do, so I tend to wind the piss out of it in 1st. Problem is, the bike loads up a lot. To the point where unburned hideous muddy fuel blows out the exhaust and the connection between the header pipe and spark arrester.
    I can't imagine putting more oil in this thing.
    #32
  13. Gordo83

    Gordo83 Been here awhile

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    aerone, here is some great advice and instruction for sealing a fiberglass tank: This is from Mike Winter. POG member.

    <TABLE height="100%" cellSpacing=0 cellPadding=0 width="100%" border=0><TBODY><TR><TD vAlign=top>[​IMG][FONT=Verdana, Arial, Helvetica]Posted - 12/24/2009 : 8:17:20 PM[/FONT] [​IMG] [​IMG] [​IMG] <HR noShade SIZE=1></TD></TR><TR><TD vAlign=top height="100%">[FONT=Verdana, Arial, Helvetica]I usually pick up my POR-15 CLEAR at automotive swap meets, but there are sources on-line that sell it as well. It seems that the amount of Alchohol in the gas which is ever increasing is the reason for the problems with the tanks. I have had a tank that never had any problems start to exhibit bubbling of the original gel-coat, but I don't drain my tanks usually.
    Here are the directions that I have provided some other people inquiring on the application for coating the inside of a fiberglass tank.

    I first wash out the tanks 2-3 times with Lacquer thinner to remove as much traces of oil as possible, rinsing them for about 2-3 minutes each time and after the last rinse, I wash it again with MEK, (Methel Ethel Keytone), or Acetone should also work, to remove any remaining traces of moisture. MEK is very toxic, so avoid breathing the fumes or allowing skin to come in contact with it. Acetone can be use in place of MEK, but doesn't have quite the drying capability as MEK. Once the final rinse is complete, the tank will be stickly on the inside due to the thinner starting to break down the fiberglass resin. Care should be taken not to over do it and collapse the tank.
    The POR-15 product I use is POR-15 CLEAR and requires no metal prep. I do use the POR-15 brand thinner and thin the mixture about 15-20% to aid in ease of swishing it around in the tank. The POR-15 websites states that is should only be thinned 5%, but thinning it a little more only slows down the time it takes to initially set up. POR-15 should not be used with any other brand thinner according to them.
    I remove the petcocks and insert temporary plugs or rolled up white duct tape in the holes which can be easily removed and reinstalled before the POR-15 CLEAR sets up. To do one tank I used 1/2 of one pint plus the thinner and once poured into the tank, I tape over the filler neck and rotate the tank several times and then drain it back into a separate container through one of the petcocks, which requires rotating the tank several more times to get the majority of it out. Once sufficiently drained, I remove the other petcock plug and the tape from the filler neck and position the tank so that any remaining POR-15 CLEAR will pool in the lower rear area of the tank, which is prone to wearing on the frame cushions and often leaking.
    Periodically check for drips coming out of the petcocks and wipe away any drips to avoid plugging of the petcock holes and requiring inserting a drill bit and cleaning them out before the POR-15 fully sets up. After about an hour check the tape removed from the filler neck and once it becomes tacky, repeat the whole process again 2-3 more times, and when finished let the tank set open for a couple of days and it will be ready for use.
    BTW, The fiberglass that I coated in POR-15 CLEAR and soaked in Lacquer thinner never did become soft or sticky.
    A pint of POR-15 CLEAR thinned 15-20% should be enough to coat 3-4 tanks if done at the same time. Once removed from the original can, do not pour it back in with the unused POR-15 CLEAR or it will cause it the unused POR-15 CLEAR to prematurely set up. Seal the lid of the unused POR-15 CLEAR with some wax paper between the lid and the can immediately after removal of the amount to wish to use, and store it in a cool place for later use, but if any gets in the groove of the can lid, you will probably have to puncture the can to get the lid off.
    Preparation for coating the exterior of a tank only requires sanding into the Gel Coat and cleaning the prepared surface with Lacquer thinner. The POR-15 clear is best applied with a brush, as thinning it enough to use a spray gun will usually cause tiny bubbles in the coating, and will require finishing with a brush anyway. Once the POR-15 Clear becomes tacky, repeat the coating process at least 2 more times. POR-15 instructions state that while still tacky your favorite primer/prep coating should be applied to bond with the POR-15 Clear to allow you to later sand the primer and apply paint. POR-15 is a very hard coating, but it can be sanded and painted later if you like hard work hand sanding for a smooth finish.
    [/FONT]</TD></TR></TBODY></TABLE>
    #33
  14. Sting32

    Sting32 Trials Evangelist

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    spooge eminating from different bikes, once the "perfect jetting for Designed Optimum RPM is found, REALLY is more than just oil in gas mixtures...

    I hope to find the article I read a long time ago, that discussed the combustion events of a 2 stroke, (heck it could be the article posted in this very thread that I havent opened yet...)

    But jist of it was, that the air/fuel mixture (in 2strokes this includes the oil of course) is explained like a PERFECT "train" of measured sizes of air & Fuel that is no matter how you looked at it, exactly as long as the piston of any engine were thinking about in this example, is in diameter, that moves at varying rates into, through, and out of any cylinder, depending on many things, but for simplicity, just RPMS.

    And when perfect designed operation and power, combustion begins when the inlet door and exhaust door are closed while that perfect train is at the perfect position on the combustion chamber, IE when the WHOLE perfect train is squished and then ignited, giving the maximum power or torque that can be attained from the design.

    the article pointed out that Combinations of porting designs, Intakes, and carbs cant do anything perfectly for more than a "range" or window of RPMS of operating, the rest is at best a happy medium attained through years of research and development...

    Basically, in theory and practice, The trick to "tunning" the power from a 2 stroke had to do with the timing the location of the perfect train in the combustion part of the cycle Since nothing is perfect bare with me as I discuss "perfect" train combustion. when combustion happens before the whole train entered the combustion chamber or cylinder, all the way through to the condition of the train was more or less already mostly leaving the combustion chamber, the power is mapable in a big curve, from 0hp to spec HP and back down to something like half of spec. most of you have seen dyno slips, right? Not withstanding all the newer tricks employed with recent technology, that can help re map velocity changes of the train, powervalves, exhaust technology. We're still stuck with our perfect theory, that the fact that physics dictates that the changes in RPM would adjust the "time" that the train arrives in cylider, to be combusted.

    Any time the whole train (the perfect air fuel mixture for any combustion cycle) is not in cylinder, the engine is basically starving, from a little bit to a LOT. A lot causes damages like detonation to simple lack of cooling from fuels that wouldnt burn at "perfect" train position, etc.

    So as I definitely oversimplefied this, above from memory (sorry): just follow me through this, that a high revving (especially older engines) a given racing type engine would typically be biting small bites of the head off the train when idling. then as you increased the revs, until the "designed" rpm was met then more and more of the train was perfectly in place, to where the optimum revs design is met, then any increased revs, the train was passing the station as it got squished, so as revs went up, less and less of the trains tail section was being bit and combusted. So also note, since it is a problem no matter how you sliced it, each case other than perfect they improvise with carbeurators operating ranges, you know them as the idle circuit, mid range, and full throttle (main jet) cuircuits...

    So on this raceing type higher revving engine, maybe past 80% of WFO, where a race engine is operated at optimum, then these woud typically bite the tails off the train as it went by, (meaning fuel/air {dont forget the oil now}) is getting past the combustion chamber ===> unburned. This means in exhaust.

    what is worse is I dealt with potential, same with idle, toss fatter trains at the cylinder, a lot at idle attempting to makeup for the trains not making it perfectly into the station each cycle of the piston, this usually caused a non perfect but rich trains to hit at idle which then seemed to "load up" a raceing engine.

    This is what is giving you the "powerband" feeling as the air fuel charge is getting to where it is "close enough" to perfect but has NOT gone past perfect, the potential seemd to increase.

    And so then since the air/gas/oil mix is movin through everything much faster in high reving duty engines, usually less oils are deposited in areas as a reserve as compared to a low reving duty cycle of a trials bike.

    So most high rev bikes mix more oil in the gas.

    It is basically because the perfect little train is way off from idle up thru closer to designed RPM ranges (the engine is biting off the head of the train less and less as the rpms increas) But the engine probably gets decent amount of good trains past design, thrul WFO where it is biting the tails off the trains, since it is a high rev design the train past cylinder is less than 20% of possible engine capasity, the top 20% of the RPMS which few actually probably bother to use... there is less air/gas/oil blowing out the exhaust, plus the higher temps, it gets burned in the exhaust more effectively.

    Trials bikes on the other hand are tuned differently, actually about polar opposite of a race engine. Ports and carbs work differently to make the "Efficient" use of that whole "perfect train" described above when at the lower to mid ranges, in this perfect world Im saying at highest is at 30-40% of full throttle. where things in general are "slower" etc. In theory the train is closer to perfect at lower RPM and the tolerance is wider from idle to designed rpm, but goes past that so quickly as revs increas (opposite of the high rpm engines) that they bite off less and less of the tails of trains as the RPMS increase past design rpm capasity. This means spooge in your exhaust, if Everything I said above was with the exact same amounts of AIR/GAS/Oil in those trains.

    So as I read in that article, that spooge from the penton could just be that the train gets past the cylinder before combustion due to the design of its time, where optimum trains are at at best, 40% of wide open, meaning unburned gas oil and air gets past the cylinder before the squish happens, leaving deposites of oil and gas in your exhaust, more of the time if you are riding down trails hard and fast on the RPM ranges. you are 60% more likely to be using that 60% of that condition tossing unburned oils and fuel into the tiny little exhausts on a trials bike, instead of it sitting in the crankcase and ending up on the piston areas.

    IMHO, the BIG thing is about all the hot air I expressed above is, the oil has to have enough molecules in the right places to protect or provide "lubrication"... So since Trials bikes usually breath in the gas and oil, which gets deposited in crank cases and pistons etc, (due to the lower velocity of the air charges) which does accumulate in those areas, more oil is there in reserve.

    Since we're really not reving the engine much, you know at most of the use of the trials engine, in a given amount of time of operation (over a typical day). This tends to aid in lubing things even when mixed with less oil. so we typically mix trials bikes with less oil, to lessen the effect of a crankcase full of oil when we suddenly need RPM's that bring with them, a "lot" of that oil, or loading up, which also lessens the spooge in the exhaust.

    MANY people get foooled by this, but the trials bike wont take prolonged operation at HIGH RPM, unlike race engines, especially when we mix our gas typically at lower oil concentrations. We only do this because the little bit of "oil" deposited and channeled to the bearings let alone piston/cylinder surfaces, goes flying out the tailpipes PLUS it gets washed away with the more prevalent GAS in the mixture being pushed through the cylinder at higher pressures those few times we are at WIDE OPEN...

    If I find that article, if it was on the web, Ill try to post the link, I thought it was very well written, and I am sure I didnt explain a couple parts. like velocity vs port and spark timing, which hoepfully wont really change the thoughts that do pertain to oil/gas mixes depending on the "Duty Cycle" of the given engine in question.

    I hope this makes sense, anyone else read that article? :wink:
    #34
  15. buls4evr

    buls4evr No Marks....

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    Gordo 83....Your jets are likely way too big. You have discovered that RICHNESS means gas/air NOT gas /oil is what you are actually burning. I have a KT255 with a 26 Mikuni. Running 50:1 my engine builder does a spl needle,a 100 main jet and a 30 pilot, 2.5 slide. You are actually running RICHER than I am at 64:1. That's all done by trial by changing down through a lot of needles and pilot jets. It is totally counter-intuitive, but the bike will keep running better and cooler as you go DOWN in jet size and leaner on your needle. They will run clean and crisp when you get them close. On different days you just alter your PAJ a touch after the bike is warmed up. Your plug is probably blk and should be medium brown. Hope this helps.
    #35
  16. Gordo83

    Gordo83 Been here awhile

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    Thanks sting32, Great information.

    buls4ever, Just checked the pilot. Main is 150 and the pilot is 25. Not sure about the needle. The plug is white with a little yellow on it. It is usually black, but this weekends trial had a long loop and I was able to wind it up on the loop.
    I would like to know the numbers on your needle and slide, if possible.
    Thanks
    #36
  17. buls4evr

    buls4evr No Marks....

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    Gordo83.......Needle is a 5C23 machined by B&J. Slide a 2.5. Your pilot may be a little small and your needle is the part that you run on all the time in trials(most racing actually) and you really need to know what that is and what groove it is set on. Raise needle to richen,lower to lean. Your main is likely way big. Note that this refers to my Mikuni 26MM roundslide so if you run a Bing in that Penton none of this is the same as they have different jets and number system. Also you are talking about a 125 vs a 255. Give Bob Ginder a call at B&J Racing. This is a set-up to run 50:1 BTW.
    #37
  18. Gordo83

    Gordo83 Been here awhile

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    I have talked to Bob several times and he has helped me out with suspension. He was unable to help out with a carb for my Penton, as he hasn't built one for a Penton Trials bike. I am running a Mikuni VM26. That's what caught my eye on your post. I have the Bing built for trials also, but it is far from perfect. I am doing everything myself, as far as carburetion goes, so it's all trial and error. I may end up with a VM24 before I'm through.
    #38
  19. aerone

    aerone Been here awhile

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    Thanks Gordo83. Great link. I'm going to give it a try. It looks like just about any of them affect the gel.
    #39
  20. b50bsa

    b50bsa Adventurer

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    I worked at a small saw mill that relied on a chain saw to cut the logs to length for the head saw. That chain saw worked, full throttle, all day long. It used a 100:1 mix.

    I would use that oil, and mix ratio, if I had a street 2 stroke. I won't use that ratio in my off road bikes.

    The saw worked at WOT all day long. It always had oil on the important surfaces.

    Every time you decrease, or close the throttle on your "2 stroke dirt bike" you do not lube the important bits. Thats why you blip the throttle on long down hills.

    Run it a bit rich on oil, I dought you will feel the difference.
    H



    #40