elusivemite Posted September 30, 2008 Report Share Posted September 30, 2008 hi just brought my 1st trials bike and have come across info on montesa,a site sugesting i use 93 octane pump gas and 105-octane race fuel at a 50 50 mix. is this critical or can i use fuel straight from the pump ? Robin ps Bike 315R Quote Link to comment Share on other sites More sharing options...
the addict Posted September 30, 2008 Report Share Posted September 30, 2008 (edited) Use the best fuel you can get, high octane etc and make sure you use good 2 stroke oil specific for trials bikes not MX or junk from the local garage for chainsaws. Avgas is good but mix it 50/50 with 97 Octane or just use 98/99 like Shell V Force, Castrol TTS is a good oil Ive always used in 2 strokes Edited September 30, 2008 by The Addict Quote Link to comment Share on other sites More sharing options...
motovintage Posted September 30, 2008 Report Share Posted September 30, 2008 hi just brought my 1st trials bike and have come across info on montesa,a site sugesting i use 93 octane pump gas and 105-octane race fuel at a 50 50 mix. is this critical or can i use fuel straight from the pump ?Robin ps Bike 315R I also ride a 315R and I found it runs best on race gas, VP C12 or VP red, when I lost my job I started to use pump gas and had to jet it up a bit to keep it from detonating, I have since found a fuel additive made by maxima (high test) that I have been pleased with, went back to my race fuel jetting and a whole lot cheaper than race fuel Quote Link to comment Share on other sites More sharing options...
elusivemite Posted September 30, 2008 Author Report Share Posted September 30, 2008 sound il hav ta look in to it. c what i can get over here one of hte downsides of living on a island Quote Link to comment Share on other sites More sharing options...
greg Posted September 30, 2008 Report Share Posted September 30, 2008 how is anyone supposed to know you live on an island ????? Quote Link to comment Share on other sites More sharing options...
elusivemite Posted October 1, 2008 Author Report Share Posted October 1, 2008 ummm coz i just said so. funny that Quote Link to comment Share on other sites More sharing options...
njtrials Posted December 29, 2008 Report Share Posted December 29, 2008 (edited) I have a new (to me) 2002 Cota and don't have a reliable source of race gas near me. I can get Av gas nearby. I think it is called Low lead 100. Pump gas here is about 92 octane. Any opinions or solutions anyone can offer? I hope to ride new years day and need fuel. Thanks. Edited December 29, 2008 by NJTrials Quote Link to comment Share on other sites More sharing options...
motovintage Posted January 2, 2009 Report Share Posted January 2, 2009 experiment and see what works for you, the 50/50 pump and av gas sounds like a good place to start Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted January 2, 2009 Report Share Posted January 2, 2009 how is anyone supposed to know you live on an island ????? read his profile? Quote Link to comment Share on other sites More sharing options...
copemech Posted January 3, 2009 Report Share Posted January 3, 2009 I have a new (to me) 2002 Cota and don't have a reliable source of race gas near me. I can get Av gas nearby. I think it is called Low lead 100. Pump gas here is about 92 octane. Any opinions or solutions anyone can offer? I hope to ride new years day and need fuel. Thanks. I have run the AVGAS for years with no problem, EXCEPT it does not seem to like hot weather and seemes to vaporlock, as it is blended to atomize well at cooler temps(altitude). Biggest problem is on hot restarts, like after a quick getoff to walk a section! Other than that, fine, and has good long shelf life! Quote Link to comment Share on other sites More sharing options...
nicks_tr34 Posted January 3, 2009 Report Share Posted January 3, 2009 (edited) Ok, just in case people are not 100%sure, first lets make it clear what Octane is in there for! The octane is in there to stop pre-ignition, or 'detonation' as it is commonly called. This is where we set the bikes spark timing before the piston reaches the top of its stroke. The idea being that by the time the mixture has actually ignited (short time delay between spark and things actually going bang!), the piston is now just starting its downstoke. Bearing in mind the speed the piston is traveling, If you only sparked after the piston was at the top, then it'd be a fair ways down the next stroke before the mixture had ignited and you won't get the max benefit (power)!! Set the timing too early and the explosion happens before the piston is at the top and it essentially tries to push the piston back the way it came again ... this puts massive stress on the components and ... well looses you power ... detonation can also happen if the compression is so high that the pressure alone is enough to ignite the fuel mix (prematurely). Ok, so that is why we set the ignition before piston is at the top of its stroke (BTDC) and how you need to set it just right, also that high compression (skimming heads etc) increases the risk of detonation. So ..... We have 2 choices .... 1: Buy the fuel that is appropriate for the ignition and/or compression settings of your bike. 2: Set the ignition and/or compression appropriately for the fuel .. Obviously choice 1 will potentially give you more 'power' .. but choice two is perfectly good. Also to be honest, in trials it is all about finding grip. Having an engine that is too lively is actually a negative thing. Therefore one could argue that using the lower octane fuel and retarding the ignition is actually the better option for trials (especially if like me you are new to trials). Here in the UK we can get 95 (standard pump) 97/98 (most super unleadeds), some of the pump super unleadeds are now 102. Then you could obviously go AV-Gas. If the bike is set up to run perfectly on say 95 octane and you have not modified your ignition or compression from that, then there is no point putting say 105 octane in as the engine won't 'do' anything with the extra octane ... its just a waste of cash ... Some modern cars have 'knock detectors' and are clever enough to adjust the timing appropriately 'on the fly' to get the max out of the fuel they run ... as far as I am aware, our trials bikes are too dumb and therefore won't reep the benefits unless we modify the timing/compression ourselves. Personally I use the 95 ron. But then I am a cheapskate!! Hope that is of some use and not just waffle!! Edited January 3, 2009 by Nicks_TR34 Quote Link to comment Share on other sites More sharing options...
grahamjayzee Posted January 3, 2009 Report Share Posted January 3, 2009 Nick, you are mostly correct, but the extra octane also provides safe headroom from knock that other things can cause. Coking is a big issue in 2 strokes and the presence of carbon causes hotspots these can pre-ignite the mixture, Higher octane ratng can delay this. There are also situations where the engine has been worked hard (such as revving out of a mudswamp!) here the head and piston crown will be very hot, again promoting a situation wher pre-ignition can occur. Higher octane fuel is a good insurance in a trials 2-stroke... Quote Link to comment Share on other sites More sharing options...
nicks_tr34 Posted January 3, 2009 Report Share Posted January 3, 2009 (edited) Nick, you are mostly correct, but the extra octane also provides safe headroom from knock that other things can cause. Coking is a big issue in 2 strokes and the presence of carbon causes hotspots these can pre-ignite the mixture, Higher octane ratng can delay this. There are also situations where the engine has been worked hard (such as revving out of a mudswamp!) here the head and piston crown will be very hot, again promoting a situation wher pre-ignition can occur.Higher octane fuel is a good insurance in a trials 2-stroke... That is a fair point, but with the advent of modern synthetic 2-stroke oils, especially at 70:1 or even 80:1 mix, and modern detergents in the fuel itself, do we still suffer from engines coking up? This isn't the 70s .... I know my minimotos rev a fair bit higher, but when I took my last one apart, there was very little carbon build up. That I ran on 95ron and Rock-oil Fully synth at 45:1. Also what is the manufactures octane rating for the bike out of the box? ... bearing in mind it is for a 'world' market, if it is say set nominally for use on 89ron (surely the manufactures are going to play it safe?), running 95ron already has wiggle room. Anyway all, as you can see, its open to debate ... apart from needlessly hurting your wallet, I am not sure there are many downsides to using higher octane PUMP fuel? Play it super safe? or just wasting money for no benefit? p.s. I know it is often done, but I think using av-gas will mean you have to know what you are doing, mix too much of that in and you will cause other problems ... remember, its not JUST octane that is in fuel ... .. so in summery, it probably isn't necessary, but if you want lots of wiggle room 97-102 octane pump gas (petrol) ... unless you have diddled with the bike, going to av-gas is probably not necessary and potentially opening up another can of worms ... and bearing in mind you already have lots of wiggle room with ~100ron ... to what gain?!!? I'm gonna stick with 95ron myself ... If for no other reason than I don't trust getting fresh batches of 'super unleaded'. As it has a much lower turnover at the pumps than standard unleaded, it can sit in the forecourt tanks for long periods .. that is a whole other story, but I destroyed a 4-stroke race engine once by unwittingly buying a stale/contaminated batch of super unleaded ... as normal 95ron unleaded has a high turnover, to my mind, I am much less likely to get a stale batch ... which again bearing in mind the timing and compression of my bike and 95ron is already on the safe side, to my mind, getting 'fresh' batch of fuel is more important than the (to my mind overkill) wiggle room of super ... Anyway, that is my 2p (cents) wroth!! Edited January 3, 2009 by Nicks_TR34 Quote Link to comment Share on other sites More sharing options...
grahamjayzee Posted January 3, 2009 Report Share Posted January 3, 2009 Anyway, that is my 2p (cents) wroth!! Given your preference for using standard as opposed to super to save money (which must be all of, ooh, 40p per trial!), are you sure you can afford 2p-worth? Quote Link to comment Share on other sites More sharing options...
nicks_tr34 Posted January 3, 2009 Report Share Posted January 3, 2009 Given your preference for using standard as opposed to super to save money (which must be all of, ooh, 40p per trial!), are you sure you can afford 2p-worth? Over 5 trials that is pint of beer!! As you can see, my rationale is more than saving a coupla pence ... its more not wasting a couple of pence for no gain and more importantly the fact I don't trust batches of super any more ... there was nothing more annoying than paying through the teeth for shell optimax (v-power now) high octane fuel and have it destroy my engine coz it evidently came out of the pump stale/contaminated!!! ... I'd probably have been better off with fresh 95 and running close to the wire tuning/detonation wise ... (my race engine had raised compression - hence running it on super) ... screw your 40p's that mistake cost me ~ Quote Link to comment Share on other sites More sharing options...
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