timing IS every little thing - an easy Kart Ignition Explained
Printer-friendly style component 2 By john Copeland
Last month we began looking at the basic principles that make the ignition system on her engine work. You"ll recall the we listed that as soon as the magnets in the rotor or flywheel ~ above the crankshaft rotate previous the windings of cable in the coil, they induce a voltage in those windings. However that "potential" doesn"t have sufficient voltage to run the void on the sparkplug. We have to "muscle the up" to about 5000 volts or therefore to have the ability to consistently ignite the compressed fuel/air mixture in the cylinder. That"s where the second winding, v a lot an ext "turns" of wire comes in. Like a transformer, it increases up the voltage to wherein we require it to gain the task done. We also looked at the magneto ignition systems offered in the Yamaha KT l00S engine, and took a rather general look at the Capacitive Discharge Ignition systems used on many of the Reed Valve 2 cycles today. The biggest share the the 80cc and also 125cc engines additionally use part variant that this CDI ignition. Now let"s look in ~ the venerable Briggs & Stratton and its "Magnetron" ignitions system. That seemed difficult to believe when Briggs told united state we could yank out
the points and condenser that had served us to well because that years and also plug that small box in your place. Well, not just does the work, but likewise it works much better than the old points ever before did. Here"s how: The magnetron coil actually has 3 different coils of windings. In addition to the main and second windings, over there is a third winding, referred to as the "trigger" coil." once the leading edge of the magnets in the flywheel method the coil, the magnetic ar surrounding those magnets generates a tiny voltage (about 1 volt) the powers a solid-state switching machine called a Darlington Transistor, turning the transistor "on." that "on" mode completes the circuit on the main winding and a current of around 3 amps operation to soil on the crankcase (Figure 2). Together the flywheel continues to revolve that current builds the magnetic field in the secondary winding.
When the trailing edge the the magnets in the spark plug gap. The flywheel will the trigger coil, a second small current is induced in the cause coil and that current tells the transistor to "turn off", successfully breaking the circuit that the main winding come ground (Figure 3). Together we discussed last month, the sudden break causes the magnetic ar to collapse. Since current (amperage) and voltage space inversely proportional, suddenly stopping the current flow reasons the voltage come "spike" as it compensates. It"s that spike that builds the voltage forced in the an additional winding to jump the sparkplug gap and ignite the mixture. Through the way, in the Magnetron coil, the major winding has actually 74 transforms of wire and the secondary has 4400. That"s a 59.5:1 ratio and also that helps insure the there"s sufficient voltage to acquire the project done. All this, the initial existing in the trigger coil, the buildup of potential, the second trigger coil pulse, and the collapsing ar with the resulting voltage spike and spark, in on around 10 degrees of crank rotation. That method that in ~ 6000 RPM the entirety thing, begin to finish, only takes around 0.00027 seconds. Quite amazing. This simple, but very effective, spark control system even advancements the ignition timing, resulting in the plug come fire previously (in degrees of crank rotation) as RPMs go up. You might recall indigenous the part on the this collection (NKN January,2000) that "the rate at i m sorry (the) potential develops determines that magnitude." In other words, the faster you turn the magnet on the flywheel past the windings in the coil, the greater the potential voltage that is developed. Because it only takes around 1.0 volts from the trigger coil to turn the Darlington transistor ~ above (and off), the quicker (in regards to crank rotation degrees) the potential build to the required 1.0 volts, the earlier the induced current in the primary side of the coil will begin to build. And likewise, the previously the 2nd trigger coil potential reaches 1.0 volts, the earlier it will turn the transistor off and trigger the spark process. Take a watch at figure 3 to see just how this developments the timing. I understand this sounds favor a lot of engineering gobbledygook. However what it method to you as a racer is, the faster you turn the engine, the previously the spark occurs in the rotation the the crank. "Advancing" the spark is something the engine tuners native karts to NASCAR have actually played v for years. Many big-car ignition systems have actually had integrated ignition advancement for decades. In more recent years, old mechanical systems to
readjust the time in the distributor have actually been changed with advanced electronic engine regulate systems. The Briggs "Magnetron" mechanism does exactly that, cleanly, efficiently, and also reliably. over there are just a few factors in the ignition device that the racer can adjust. Part are relatively simple and also tuning with them is common practice. Others require innovative machining and fabrication work. Still others are just a issue of swapping components. In any kind of case, you deserve to make some transforms that will have actually a dramatic effect on exactly how your engine performs through working with the ignition system. Let"s begin by see what happens once we start fiddling through the Briggs. probably the most typically used ignition-tuning device on the Briggs & Stratton 4stroke is the offset flywheel key. Every kart shop carries them and also the savvy Briggs racer tote a selection to adjust the engine come the track. Basically, these little machined pieces replace the stock Briggs 1/8" X 1/8" flywheel key. Although they room sometimes marked in thousandths of an inch offset, much more commonly lock are figured out by degrees of offset. In other words, how numerous degrees that crank rotation perform they move the flywheel indigenous the share position. Many engine home builders building methanol-burning Stock-class engines usually send their engines out the door v 5 degrees or for this reason of offset. That amount of breakthrough provides a sensibly safe performance increase without too numerous headaches because that the less experienced or adventurous tuner. Component of that improved performance come from starting the combustion process itself earlier and also thus optimizing the allude at i m sorry the burning chamber push reaches that is peak. Another part comes native the reality that the methanol/air mixture burns somewhat much more slowly 보다 a gasoline/air mixture for which the engine was designed. So friend gas-classers the end there take note; 2 or 3 levels is a better place for you to start.
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One point to be careful of, silly as it seems, is that you counter the crucial the exactly direction. You want the sparkplug come fire earlier in the crank rotation, as soon as the piston is farther under in the cylinder on its way up. That means that, as soon as viewed indigenous the flywheel side, through the starter or starter seed removed, together with the washer, the keyway slot in the flywheel should be closer to top-dead-center than the keyway slot in the crankshaft, as the keyway rotates up toward the coil (Figure 4).
Ok out there, l watch you rolling your eyes. But 1 have actually seen engines come in v the flywheels counter the dorn way. And believe me, retarding the spark 5 levels or for this reason won"t perform anything to help your performance.
Anyway, what happens as soon as you move up or under from the 5 degree beginning point? Offsetting the flywheel even an ext helps the engine achieve much more complete burning at greater RPMs. Starting the fire earlier, friend know. But an ext combustion time in the cylinder method more heat soaked up in the block and head too. You"ll gain top end but you"ll most likely need a larger jet to keep the heat listed below the 380?390 level upper limit. If you"ve clogged off part of the air intake ~ above the fan shroud you might want to open up that back up a bit. Most tuners aren"t afraid to go approximately 7 or 8 degrees, but couple of venture past there. Unfortunately, the top-end rise comes at the price of short end. And on monitor where obtaining off the sluggish corners is the difference in between winning and losing, that"s a poor trade. In cases like
that, an competent tuner minimize the flywheel counter to 4 or also 3 degrees to boost low RPM performance. Because the fuel/air mixture constantly burns, more or less, in ~ the very same speed, if you require the engine come be at its ideal at reduced RPMs also much advancement can relocate the peak burning pressure earlier so early on in the crank rotation the it actually resists the momentum of the crank and flywheel and hurts performance. That course, to get the optimal fuel mixture at these reduced RPMs, and also to aid get the heat up into the wanted range, you might need a smaller sized jet if yon alleviate the balance out in the ignition. Closing off few of those air join in the shroud may help get the heat up too.
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There"s only one trouble with offsetting the flywheel crucial to get the timing where you desire it. The folks at the Briggs factory took an excellent pains to balance the flywheel/crankshaft/piston/rod combination for smoother to run and much better performance. Offsetting that vital upsets all that carefully engineered balance, and that damages performance. So are you shack having actually to select one element over another? no necessarily.
Next month we"ll look at at how you can obtain the time you want without offering up too much in the balance area. Climate we"ll conclude this look in ~ ignition equipment by analyzing what various other adjustments and also tuning features each device offers and also what impact those adjustments can make. See you then.