liviob Posted October 10, 2011 Report Share Posted October 10, 2011 My 09 290 EVO uses the BR7ES plug. Maybe four months ago i changed the plug for the first time since new due to a rough runing low rpm range. After inspection of the plug i noticed that it was begining to foul due to oil contamination. The engine ran like new with the new plug. It is begining to run rough again at low rpm. I used to run the standard plug gap which i think is .024-.026? Im not sure at the moment unless i go look at the owners manual. A freind recomended that i set the plug gap to .020 for better bottom torque. Im thinking that this smaller gap setting is causing the plug to foul. It's the only thing that i have changed in the combustion process. What do you think? Do any of you have exeriance experimenting with plug gap. I plan on installing a new pug set to the standard plug gap. Quote Link to comment Share on other sites More sharing options...
famousamos Posted October 10, 2011 Report Share Posted October 10, 2011 Was the carb rejetted after purchase? What oil mixture are you using? Fred Quote Link to comment Share on other sites More sharing options...
liviob Posted October 10, 2011 Author Report Share Posted October 10, 2011 No carb changes other than lowering the needle one clip and the occsional air screw adjustment and the same opti-2 oil and ratio of 70/1 since new. I changed the plug gap four to six month prior to the last plug change. Quote Link to comment Share on other sites More sharing options...
chewy Posted October 10, 2011 Report Share Posted October 10, 2011 Take it for an occasional blast ( a few miles of road?) Is your exaust full of oil also?.. when you give it a blast you'll find out. Quote Link to comment Share on other sites More sharing options...
liviob Posted October 10, 2011 Author Report Share Posted October 10, 2011 I took a moment to look in the owners manual to see what the plug gap specs are and it says .5mm-.6mm which is equivelant to .020-.024. I guess since my plug gap is .020 the plug may not be the issue here. Quote Link to comment Share on other sites More sharing options...
copemech Posted October 11, 2011 Report Share Posted October 11, 2011 I took a moment to look in the owners manual to see what the plug gap specs are and it says .5mm-.6mm which is equivelant to .020-.024. I guess since my plug gap is .020 the plug may not be the issue here. Livio, there is a lot of science, and a lot of simple logic it seems behind all this. Far too much to get into here, as I am not a good typist! I have nothing Beta specific for you, yet systems are all similar in the fact they are all still limited to what is a limited system as used on trials bikes. Basically a magneto system, less points! To light off fuel/ air mix, you need spark, and the better exposure you can give to the mixture yields the best results(flamefront propagation), thus, run your gap as wide as reliably possible for the ignition to support. At your altitude, I think you could run 0.7mm or .028 or even more, with no problems due to decreased air density(resistance the spark has to reliably jump). This is what provides better power at lower speeds. Plug fouling, in a 2T, oil is an obvious enemy. You gotta keep it burnt off, and trials conditions are not allways conducive to that, takes some heat in the motor and a good run and load to blow out excess oil and heat the thing up!. I try to do at least one good run every startup just to keep things clean, less they load up and fail! Daily ride maintenance! Rev it out till it clears under load! Good thing here is standard plugs are disposable, chunk them at the first indication of poor running or hard starting. I think the platinum and irridium plugs may offer some advantage as well, in resistance to fouling and better flamefront exposure due to the smaller and more open electrodes, yet if not maintained, you have just fouled an expensive plug. Best I recall, my current platinum plug came out of my '05 bike, went into my '07 bike, and is still there, at least for today! And at .028 on the Sherco. Quote Link to comment Share on other sites More sharing options...
liviob Posted October 11, 2011 Author Report Share Posted October 11, 2011 Thanks for the replies. All good thoughts. Thats what i was thinking Copemech since the gap is the only thing i have changed and i have fouled two plugs since the change in gap setting. I will go back to a larger plug gap setting. Quote Link to comment Share on other sites More sharing options...
jse Posted October 11, 2011 Report Share Posted October 11, 2011 Plug fouling, in a 2T, oil is an obvious enemy. You gotta keep it burnt off, and trials conditions are not allways conducive to that, takes some heat in the motor and a good run and load to blow out excess oil and heat the thing up!. I try to do at least one good run every startup just to keep things clean, less they load up and fail! Daily ride maintenance! Rev it out till it clears under load! I would think (and based on my experience) that a well-maintained and properly jetted 2T does not need to be cleaned out at every startup. I'm also quite surprized that the EVO runs a non-projected tip plug, two steps colder than the normal heat range in a liquid-cooled Trials bike. They must have made some radical changes to the combustion chamber. Jon Quote Link to comment Share on other sites More sharing options...
liviob Posted October 11, 2011 Author Report Share Posted October 11, 2011 (edited) You brought up a good point Jon. I had been thinking of trying a br5es like i use in my 250 rev3. Only because if changing the plug gap a few thousandths cools the plug enough to cause it to foul then maybe a hotter plug would be better. I used to weld for a living and a technique i usd to control the heat of the puddle while welding was to vary the length of the arc. A short arc would cool the puddle and a long arc would produce more heat. I think changing the gap of the plug would produce the same results. When i used the larger plug gap i did not foul plugs. What is a progected tip plug? Edited October 11, 2011 by Liviob Quote Link to comment Share on other sites More sharing options...
copemech Posted October 11, 2011 Report Share Posted October 11, 2011 (edited) I would think (and based on my experience) that a well-maintained and properly jetted 2T does not need to be cleaned out at every startup. I'm also quite surprized that the EVO runs a non-projected tip plug, two steps colder than the normal heat range in a liquid-cooled Trials bike. They must have made some radical changes to the combustion chamber. Jon Jon, I should have said "every outing" as I do allways try to give things a good run at some point. It does seem to me that short runs between sections, shutting off the bike to walk sections and such, then more cold starts are kinda hard on things. They really doo cool off quickly in the winter months. As an afterthought, some of this may also depend upon your last name. Raga, Cabestany, and a few others come to mind! Edited October 12, 2011 by copemech Quote Link to comment Share on other sites More sharing options...
billyt Posted October 12, 2011 Report Share Posted October 12, 2011 (edited) JSE, Livlob, Cope Can I inject on this topic if I play nicely? LOL I do not want to turn it in to another suspension article were I got off on the wrong foot by getting all pished off at you know who! I want to try and clear the air on common misconceptions around spark plugs! I am sure you three know this stuff but rather I want to share it with those who do not! Pretty please! Edited October 12, 2011 by BillyT Quote Link to comment Share on other sites More sharing options...
copemech Posted October 12, 2011 Report Share Posted October 12, 2011 JSE, Livlob, Cope Can I inject on this topic if I play nicely? LOL I do not want to turn it in to another suspension article were I got off on the wrong foot by getting all pished off at you know who! I want to try and clear the air on common misconceptions around spark plugs! I am sure you three know this stuff but rather I want to share it with those who do not! Pretty please! Spill your bleeding liver, Billy! Quote Link to comment Share on other sites More sharing options...
liviob Posted October 12, 2011 Author Report Share Posted October 12, 2011 (edited) Ok BillyT, I would like to hear your thoughts about spark plugs . Edited October 12, 2011 by Liviob Quote Link to comment Share on other sites More sharing options...
dan williams Posted October 12, 2011 Report Share Posted October 12, 2011 (edited) If you're running pump gas it's about the time of the shift over to "winter" gas. If you're getting four months on a plug it's not that severe. Oh just noticed location, perhaps a little rich due to altitude? Edited October 12, 2011 by Dan Williams Quote Link to comment Share on other sites More sharing options...
billyt Posted October 12, 2011 Report Share Posted October 12, 2011 (edited) Okay since you insist! LOL Warning it will be long and confusing due to my long winded writing skills! The thoughts below are mine, may be controversial but mostly based upon scientific fact, and some basic fundamentals and common sense, really! Feel free to tell me I am full of crap, if you do then help me see your point of view! Firstly the fuel air mixture is ignited by the UV portion of the spark wavelength, approx 360 nano meters! In my opinion the setting of the gap in the plug is somewhat of a misnomer, and the hot plug, cold plug is mostly misunderstood. Let me try to elaborate! Plug Gap: Every ignition system out there on a motor bike has the ability to produce electrons that will jump across the gap to complete the circuit. This gap has a very small range that it will be effectively functional to producing a strong spark or circuit completion. Common theory states that "Too big a gap and the signal will be weak, too small a gap and the signal will be weak", "make the gap large for better low speed running"! I beg to say that the gap has absolutely nothing to do with low speed running etc. All these statements are in my mind, education and experience nothing more than urban myth (sorry Cope). Here is why I make this statement. The gap in a plug is a mechanical and electric function of the mag that it is connected too. The gap range/adjustment is there to match the ability and strength of the mags ability to pump out enough current to jump a gap. Thus the range adjustment in every plug is there to find this efficiency, once set, unless one changes to a different type of mag there should be no need to do little tweeks to the gap! It is basically matching the gap to get the best out of the mags ability. Simple so far? BUT here is where the crazy part comes in to play. The bigger the gap (within the effective range of the mags output) in other words widening the gap at the widest part of its effective range will afford a spark that is longer in duration, NOT necessarily HOTTER. The pre determined gap by the bike manufacturer is there to match the plug to the current output of the mag that they are using in the bike. They have experimented and found the best gap to give the best spark (best spark means good current flow and also letting the flow of current stop). I will come back to that momentarily! On a modern gas stove or fireplace there is a piezo for starting the gas to burn. Turn on the gas and press the ignition switch (activating the piezo causing a spark) this in turn ignites the gas and the gas keeps burning even though the piezo igniter is turned off. The fireplace or stove does not burn any better if you keep the piezo activated does it? If you had a pressurized can of ethanol (like a paint spray can) held it up and pressed the nozzle and then held up a BIC lighter, struck it, the spray would ignite as long as the ethanol fuel was flowing even though the lighter was turned off after the initial ignition of the fuel, As long as there was fuel that was ignited by the initial spark any subsequent fuel would burn whilst one held the nozzle down. The fuel spraying out the can would not burn any better, hotter if one kept the flame of the lighter lit! So, we only need to ignite the in coming fuel and then the flame will propagate and burn any subsequent fuel that is still coming in regardless if the initial spark is gone! So back to why I said contradict myself? If the wider gap does not make the burning gas any hotter then why make gap as big as the mag can a handle? In my opinion it is a timing thing! There is only one pulse per revolution and the in coming fuel air mixture only needs to be ignited flame propagation will do the rest. Having a wider or smaller spark plug gap from the optimum gap will not make the spark hotter or colder. The synchronization of spark to the fuel and air being at the correct part of the cylinder head (at full compression hence why we fire the plug before top dead centre to afford full spark and in length and current) at the right time is the key to why the gap setting. Having a spark that is at its most efficient due to the gap for the longest period to match the incoming vacuum cycle imperative. The correct gap not only affords the best current transfer equating in a good spark but also taking full efficiency of the electrical pulse thru its pulse cycle reaching full potential quicker and longer. The length of the spark is critical to burn propagation from a timing aspect. The on and off cycle of the spark plug critical to efficient RPM's. The proof of this is that you can have the best spark, but if it comes at the end of the vacuum cycle (and after full compression at the head) when most of the gas is pouring out the exhaust transfer port then it does you no good. If the spark starts at just the right time it will start the burn and then propagate until all the fuel is burned even though the spark has subsided. Having the spark reach its strongest signal a the correct time is not just a function of the ignition timing alone, gap and ignition timing both play a part in this equation. The gap in a plug is set to find the perfect balance between of the energy from the high tension coil. The low voltage, relatively higher current energy coming from the mag to the input to the coil is then stepped up to a higher voltage and somewhat lower current at the coils output (high tension lead to the top of the spark plug). That resident energy has to consume or share some to jump the gap, once the gap is bridged it then has to flow across the gap and go to ground, the current or UV portion of the current ignites the fuel. Too small a gap and not enough current is drawn but is easily bridged, a larger gap takes more energy to bridge the gap and then draws more current to keep the energy flowing, but runs out quicker due to the mag pulse being past its firing point! This effect can be seen in the contacts of a regular switching relay. The other function of the gap is as follows: If you look at most relays that are passing high current repeatedly thru the point they are burnt black by the current or EMF phoneme. The current wants to keep flowing when the contacts open and tries to arc across the opening contacts and does so by supplying or drawing more current hence why the contacts go black as the metal melts and carbons eventually. This high current erosion will eventually eat away at the contacts making them all jagged and uneven causing them not to make good contact when they do close. They will get to the point when they need to be burnished and then eventually replaced. The point is that it takes current to jump the gap in the plug, too big a gap and it takes a lot of energy leaving very little to flow once the current bridge is made. This bridging takes time as well as energy! This relay example is mentioned as the flowing current across the gap has to stop as some point. This is not purely left to the firing time alone (mag past ignition time) as the signal gets weak or cut off from the mag it the plug will still try to draw current. Having the gap wrong can keep this spark going at the wrong time. If a trials bike is turning over at 3000 RPM that equates to 50 pulses per second. That is very quick, basically it has to fire and stop firing in a VERY short time period yet still have long enough and strong enough spark to ignite the fuel. If this stopping and starting of spark at the gap was not desired then high current could be supplied continuously from the mag thru the coil to the plug resulting in the fuel being ignited even before or at top dead centre and that would be a bad thing! As the bike increase in RPM its firing pulses get quicker, but the rate the fuel burns at is constant. I am going to guess that the firing pulse from the mag is much shorter than the burn rate at higher RPM's? If one could see a graph of the spark plug current across the gap it would be an arc as it climbs and descends all this within a VERY short time frame yet only ignites the fuel at near the top of the curve. The gap plays two roles helping the current flow creating spark and helping the spark stop drawing current due to back EMF. The gap distance acts like a mechanical brake helping to break down back EMF as the current flows down the back side of the curve it does not have the energy to keep firing or rather draw more current. That concludes my theory about the plug gap being more about a timing thing than just a hotter or colder spark at low revs compared to high revs being set by the gap. In conclusion set the plug at the recommended gap and leave it alone. If the plug is fouling it has nothing to do with the gap. If you think you are making the bike run better at low RPM by changing the gap please tell me how that works? : As for hot plugs and cold plugs that is nothing more than the ceramic shroud that affords the plug to retain heat or dissipate heat. A hot or cold plug does not make a hotter or colder spark.. period! A protruding plug tip extends more into the incoming mixture of fuel and air combustion area, some say it gives you a cleaner burn and also increase compression by consuming space? The spark generation or circuit completion of a plug is also subject to being blown of course or out by the incoming fuel air mixture. If the gap is too wide the spark can be blown off course and not make contact with the other side of the plug tip. That is why drag racers etc used to index their spark plugs, they tried to turn the spark away from the in rushing fuel and air mixture. I agree with Jon that a modern trials bike should not need to be cleaned out all the time. The excess smoke out the exhaust is mostly the function of the oil and gas separating in the crank cases and stinger. Why? The oil and gas mixture is swirling by many rough surfaces (kept rough deliberately to keep the oil and gas mixed and swirling) when the mixture is down in the crank area before it is transferred up the ports in the cylinder at low RPM/s there is not enough head on the vacuum subsequently the heaver oil tends to separate from the gas sticking to the rough surfaces. A bye product of this effect is also engineered in to help lube the lower end. When you rev out the bike there is more vacuum pulses per minute thus a more constant vacuum (not stronger) pulling up the excess oil from the prior separation at lower rpm/s. This effect is not as obvious with todays oils, but in the past it was an issue. Keeping mind that the oil in your gas mixture does not burn on each stroke but rather is used for lubrication and most of it gets blown out the exhaust pipe with some of it staying in the end stinger. The higher pulse rate or exhaust scavenging at higher RPM's help blow it out. Livlob. You said you changed nothing yet your plugs are fouling! Are they cold fouling or hot fouling? Two different scenarios of what to check! As for Dan's comment I agree that the problem may not be the plug but rather your fuel type or weather related. Knowing if you are popping a plug (hot lean foul) or cold (rich) fouling a plug is important in figuring out what is going on! It is VERY hard and unreliable to pull a plug out and look at its colour and change jetting based upon the colour. I know, I know people tell you to do this all the time. Urban myth! When you read a plug what are you reading. Pilot jet, Needle, Slide, main jet? They all contribute to how the plug gets carbon and or fuel deposits on it. Or in fact how hot the plug gets due to the fuel/air mixture being to hot i.e. lean. If we agree with this statement then think of the following: A normally run trials bike has the throttle opened all thru the carb ranges i.e. pilot jet, needle, slide, main jet. All of these jets, slides and needles contribute to various amounts of fuel to air ratios to the cylinder/plug. The main jet supplying the largest amount or contributor. I am totally confused when a guy pulls a plug looks at it and states "the pilot jet is too lean" how the hell can he say that when he has just exposed the plug to fuel from the pilot jet, needle, slide and main jet. The pilot jet could be just fine or even rich, but due to him opening up the throttle and the maim jet taking over maybe it is very lean causing a lean condition on the plug????? The best way I have witnessed is to get all the jets in the bike, (after of course you have warmed up the bike with what ever jest you had in it) new plug and only open the throttle up to the pilot jet. Pull the plug, if all is okay, put the plug back in, ride and open the throttle to the needle, pull the plug if all is okay move on, keep doing this all the way until you get to the main jet. If you are now at the main jet you ride and pull the plug and it is lean or popped then you know it is primarily the main jet you are reading! All the jets play a part in a wide open throttle but this way helps you break down what part of the carb is causing plugs to go out on you. Plugs can go bad from way too lean a condition and/or way to rich a condition. WHEW... sorry for being so long winded............ Edited October 12, 2011 by BillyT 1 Quote Link to comment Share on other sites More sharing options...
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