Setting “Pulserless” Ignition Timing on 2-Stroke Engines Many of our ignition kits are designed specifically for an individual model so there is no timing to adjust, however a few do require the owner to set them up (and give the option to experiment). Adjustment of 2-stroke ignition timing has always been seen as a bit of a dark art, however if you understand the principles involved, setting the timing is not difficult once you’ve done it a couple of times, even when there are no timing marks. If you work methodically you can achieve a much higher level of accuracy than timing marks on mass produced parts. Two-stroke engines operate in a very dynamic fashion; 3 things need to come together to produce real power: porting, expansion chamber design and ignition timing. 4-stroke engines are far more straight forward in their requirements, two-strokes are not. For example you cannot keep the ignition fully advanced as the RPMs climb on a 2-stroke. When the porting and expansion chamber are coming together give maximum power, the timing must start retarding off.
How to proceed with no timing marks when installing a variable timing ignition. Initially you are going to have to use a DTI, strobe lamp and and a little ingenuity. A protractor may be useful if you want to convert mm BTDC to degrees. The object of the exercise is to create a series of timing marks on the flywheel that relate to a fixed mark on the engine case. Firstly decide what you want to use as a fixed marker, a piece of wire or a machined down bolt are ideal. Next we create a mark on the flywheel to show TDC. Then we add our timing marks a set number of degrees or mm before top dead centre (BTDC). The reason for marking TDC is to make life simpler in future. Once the initial marking of the flywheel is done all you’ll need to is set the piston to TDC, align the pointer to the TDC mark on the flywheel, then you are ready to check the timing with a strobe lamp. Thats’s really all there is to it, so now lets break the process down in to stages. 1. The initial marking of the flywheel is the most laborious job and requires a DTI, engineer’s set square, the factory ignition timing figure, a fixed index and possibly a degree wheel. First accurately set the piston to TDC, mark the flywheel to correspond to the fixed index marker you are using (see picture below). You can buy special DTI adaptors to fit the spark plug threads but often you are prevented from using this adaptor with the engine in the frame due to a lack of clearance with frame or exhaust. Often it proves just as quick to remove the head and use a normal DTI as we did.
Here you can see the basic set up, we firmly clamped a piece of steel to the top of the engine to give the magnetic base an anchor. We wanted to convert the mm figure in the manual to degrees so we used a standard plastic 360 degree protractor that we drilled to closely fit the end of the crankshaft.
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Setting “Pulserless” Ignition Timing on 2-Stroke Engines The pointer is fixed to the engine. Ideally the pointer should be as close to the protractor as possible to avoid viewing errors. In this example the protractor stands away from the pointer as this flywheel is fitted with extra weight for trials riding. The road version did not have the extra weights. Ensure the flywheel is properly keyed to the crank shaft and the engine is set at TDC by observing the DTI. Make a small precise mark at the pointer’s tip. Next we are going to remove the fly wheel and extend the mark. You can also use a dead stop to determine TDC, although highly accurate, due to the high likelihood of piston damage if there is any attempt to start the engine with the stop fitted we don’t explain this method. There are plenty of on-line videos if you are interested.
Using your set square extend the mark that you made in to a nice clear, straight and square line on the flywheel. I used a permanent marker first so that when I scribed the metal the line showed up clearly in the picture.
In future you can use a basic TDC indicator in the spark plug hole to set the piston to TDC, then align what ever pointer you are using to the TDC mark on the flywheel. Doing this ensures your pointer in correctly set ready to check the ignition timing.
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Setting “Pulserless” Ignition Timing on 2-Stroke Engines 2. With TDC marked we can refit the flywheel and continue this process, this time adding marks before the top dead centre (BTDC). Check which way the engine rotates! If you don’t have the factory timing figure already you will need to do some detective work to find it, this is not something we can help with, you should consult the shop manual for your machine or a specialist mechanic. Some flywheels may already have marks on but be cautious of these, they may be static, partial or full advance marks. Its best to find out what the actual factory figure was. Because you are changing the type of ignition for one with variable timing the original setting becomes a guide rather than a fixed value that you absolutely must adhere to. 3. If your engine had points the timing figure is a static figure however if your bike had CDi ignition it may be an advanced figure. If the book says “2.8mm BTDC at 2,500 RPM” you know this is an advance figure and therefore the timing at idle will be different. 4. Accurately set the piston to TDC, the pointer should be perfectly aligned with your TDC scribe mark. If it is not, re-align the pointer so that it is. Now set the protractor so the pointer lines up with “0” degrees, tape this in place, this will allow you to convert mm BTDC to degrees of crankshaft rotation and vice versa. This information can be very useful to have written down, usually 0.1mm increments is more than sufficient. Alternately just mark the advance positions on the flywheel. I prefer to mark the factory figure plus a range of marks either side in uniform increments. Doing this will give you an accurate idea where the ignition is (how many degrees advanced or retarded). You can use 2 or even 5 degree increments, its unlikely you will need to add marks every degree. It is very important to get your lines straight and square using the method shown. A second mark is made, use the factory ignition timing figure so you can reference the factory timing, then add a range of marks either side. These will show you where the timing is. Your marks should be in equal increments, these have been marked in red for clarity in the picture.
Original advance figure
Note we show a piece of wire as an index, if you lose the original pointer you can make a new one and adjust it to align with the TDC mark on the fly wheel when the piston set at TDC.
5. With the flywheel marked it’s now a simple case of fitting an inductive clamp type strobe to the HT lead, starting the engine and setting the timing to the timing mark with the engine idling. You can rev the engine and look at what the timing is doing but be aware that most strobe lamps are designed for cars and do not like the high speeds that motorcycle ignitions operate at, many may fluctuate or stop working as the RPMs climb, this is not an ignition fault, its simply that the capacitor that fires the strobe tube cannot recharge quickly enough. To adjust the timing on some of our kits you have to rotate the stator plate in relation to the crank case, some feature ©Powder Mill Electronics Ltd 2017. All rights reserved
Setting “Pulserless” Ignition Timing on 2-Stroke Engines electronically adjustable CDi units, others are fixed IE the stator locates positively to the engine and the timing is fully controlled inside the CDi unit.
Now lets understand the basics of performance 2-stroke ignition timing. With a 2-stroke, you can use ignition advance to boost the low and mid range power dramatically as well as help the expansion chamber make more power from the engine in the higher ranges. Backing off the ignition advance is essential as it protects the piston from excessive heat by moving it in to the expansion chamber, which if correctly designed for that engine will help purge the cylinder and pull in more fuel, making more power on the next ignition event. If you do not retard the ignition, the engine will seize or burn a hole in the piston. This is why 1970’s 2-strokes with points ignition had a reputation for being difficult to set and for seizures; the factory timing was set so close to the danger area at high RPMs it didn’t take much of an error adjusting the timing to cause problems. So already you can see that a fixed timing system such as points or the first generation of CDi units which also gave no timing variation will always be a compromise, one that translates in to an engine with a very narrow band. The second generation of Japanese ignitions (DT400 1978, RD250 LC etc) did make the engines more tractable with wider power bands as these gave a limited amount of advance as RPMs climb (but no retard, hence the small advance). These were non adjustable and maintenance free which made people feel confident about buying a powerful 2stroke, hence they grew in popularity. Things really got interesting with the TZ125G and TZ250K, although not road machines, these featured ignitions that initially advanced but then retarded back as the porting chimes in. The result is history; two strokes with wide power bands and reliably producing large amounts of power without seizures or holed pistons earlier machines suffered Liquid cooling and forced oil lubrication also ensured more reliability. Because our ignition kits do retard at higher RPMs they are less likely to be dangerous to the piston, certainly they are much safer than improperly set points or early CDi ignitions. Because we design and manufacture our own electronics rather than using an ‘off the peg’ CDi unit across a whole range of models (as many of our competitors do), we can build in different timing curves and have selected ones proven to work well with a certain engine. Finally tuning engines is an art, if you get it wrong it becomes an expensive one. When you modify your engine, the onus is on the person doing the work to ensure it is set up correctly and is running safely. Even something as simple as variation in chemical composition of modern fuels can affect the way the engine runs. If you allow an unhealthy combination of factors to combine you will run in to problems that can lead to engine damage. Also its not uncommon to find on older engines that a previous owner has altered the porting, compression ratio or made any number of un-noticed changes, so don’t assume, investigate first. The surest way to improve your engine’s performance is to have it professionally set up by an expert familiar with both the engine and the discipline you are riding in. Our technicians are not engine tuners, we are electronics engineers who work with engine tuners to provide systems they ask for.
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