tntrials Posted March 22, 2012 Report Share Posted March 22, 2012 I am the proud new owner of a 2001 Sherco 125. The previous owner kept the bike in great shape and informed me of a few things to do to keep it that way. I understand and agree with all except for the suggestion to run premium 93 octane or better. This isn't a money thing rather it conflicts with my experience over the many years I've had with internal combustion things. For starters, the spark plug. Sherco recommends an NGK with a "5" heat range. This is a pretty hot plug, NGK plugs are hotter the lower the number. Compared to the fleet of modern 4 stroke hyper sportbikes with agressive everything, compression, ignition timing, cam timing etc. which run a "9" or "10". Most 2 stroke motorcross bikes use a "7", "8" or "9". Lawn equipment use a "4" or "5".....my point being you can tell alot by what plug the manufacturer specifies. A "5" heat range plug and "high octane" sorta contradict each other. Has anyone tried regular American pump gas, the 87 octane variety? I have experienced wonderful results in my more mildly tuned engines like easier starting, higher idle and crisper throttle response. I have not experienced knock/ping/detonation and would imagine the engine would be cleaner running lower octane as it burns more easily and completely. Quote Link to comment Share on other sites More sharing options...
copemech Posted March 23, 2012 Report Share Posted March 23, 2012 I am the proud new owner of a 2001 Sherco 125. The previous owner kept the bike in great shape and informed me of a few things to do to keep it that way. I understand and agree with all except for the suggestion to run premium 93 octane or better. This isn't a money thing rather it conflicts with my experience over the many years I've had with internal combustion things. For starters, the spark plug. Sherco recommends an NGK with a "5" heat range. This is a pretty hot plug, NGK plugs are hotter the lower the number. Compared to the fleet of modern 4 stroke hyper sportbikes with agressive everything, compression, ignition timing, cam timing etc. which run a "9" or "10". Most 2 stroke motorcross bikes use a "7", "8" or "9". Lawn equipment use a "4" or "5".....my point being you can tell alot by what plug the manufacturer specifies. A "5" heat range plug and "high octane" sorta contradict each other. Has anyone tried regular American pump gas, the 87 octane variety? I have experienced wonderful results in my more mildly tuned engines like easier starting, higher idle and crisper throttle response. I have not experienced knock/ping/detonation and would imagine the engine would be cleaner running lower octane as it burns more easily and completely. I see where you are coming from, yet one may need to use a bit of inverse logic on a trials bike. Firstly, the Mfg. recco is 98 RON for most all models I recall. This roughly is equal to our (US) R+M/2 rating of 93 octane, and the bikes seem to run fine on that with little exception. The bikes are basically tuned for torque and rapid response, you may lug and chug it around a trials course at moderate rpms and never really get a lot of heat in the motor enough to warm the gear oil on a cold day. And they will cool down quickly. Fairly hot plug keeps excess oil burnt off as well. Compressions are still yet fairly high, for decent power and response, and the larger 250 and 2.9 need the juice to prevent pinging, as well as a fairly hot plug to prevent fouling when putting about. A 125 is not much different, yet one must carry more revs at most times, I had an '03 125 for several years, and it seemed less finiky in the fuel and jetting than my big bike. There was also some brief dyno testing done back i n that time period that supported the theory that a bit more power was to be found in the lower octane fuel when using a 125 for testing, Yet keeping out of the preignition and detonatation range is still important. Your mileage may vary! Quote Link to comment Share on other sites More sharing options...
tntrials Posted March 23, 2012 Author Report Share Posted March 23, 2012 Ok, that makes sense. Compression ratio pretty much dictates octane regardless of how much you keep the engine wound up, it can ping even at low rpm with too low octane. A hot plug would/could cause issues if the bike was ridden wide open for extended periods of time like an MX bike. I've run hotter plugs in MX bikes when luggin' thru the woods so they were less likely to foul and leave me stranded. Had to be careful about holding it wide open for long periods though. Since Trials bikes aren't held wide open rippin' thru the gears very often the high octane/hot plug combo makes sense. Quote Link to comment Share on other sites More sharing options...
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