[Just to lay credit where it's due: My own tip was to use the specifically-bought Sure Start (aka Easy Start) spray ... the bit about using gas (and therefore virtually without cost) came from another chap in this group (was it The Natural Philosopher?). Thomas P also told us that you can squirt the "rocket assistance", whatever it might be, on to the air filter without taking it off, which will save me some faffing about in future :-D ]
Also Al: you never said to start with that:
... eee well! So you actually LIKE taking engines apart! Have fun -- I'm more of a arty-type myself :-)
In my original 'vanity/proof reading' scan, I *had* used the correct "maximum" word in the above statement. However, even I managed to get sufficiently confused as to change it to the word "minimum". Apologies everyone (I do see other posters' justification for criticising my often overly long (and flowery) postings. :-(
====snip====
understand,
I suspect this must a modern hybrid version of the magneto system where the functions of a self contained magneto were split into a seperate generator (permanent magnet rotor keyed directly onto the engine crankshaft) feeding ac current to what would otherwise be a conventional ignition coil and CB arrangement normally powered from a battery. The keying of the rotor of the PM alternator guaranteeing that the current would always be interrupted at the peak of the generator's waveform.
The generator would also be used to provide electrical power to headlights and instrumentation (speedo and main beam warning) lamps, usually from seperate generator coil pairs (it was common practice to split the generator output into two sources (using either 50:50 or 34:66 ratios) and combine them according to load demands using auxiliary switch contacts on the side/head light selector switch as a crude charging control in a battery set up or else to avoid burning out sidlelights when the extra power wasn't required in a batteryless system (typical of mopeds and some models of motorbikes, usually models designed for scrambling events or bush trail riding where the battery would be an unnecessary luxury and a liability).
In this case, the flywheel generator is most likely powering a contactless "transistor assisted" ignition module circuit and coil hidden under that plastic cover. The ignition timing will most likely be triggered by a magnet and pickup coil sensor (avoids mechanical wear and tear, hence the 'benefit' of the additional 'electronics' which might literally be emulating the original magneto idea, replacing the CB points with a high voltage switching transistor interrupting the appropriate polarity peak current of the ac output taken directly from the generator winding or, a little more sophisticated, triggering a capacitor into discharging some 400v into the low voltage winding of the ignition coil to generate the necessary 30 odd KV spark pulse almost regardless of any leakage (damp or fouled plug insulation).
In this case (Capacitor Discharge Ignition) the ignition coil is only being used as a step up transformer, not as in the original case, for its inductive properties to generate the necessary 400v pulse *and* its step up transformer action which relied on there not being any leakage in the HT side to compromise its ability to rapidly turn off the 3 or 4 amps of current flowing in the inductance of the coil's primary winding fast enough to produce the required 400v pulse of back EMF.
Whilst a CDI has a bit more complexity than a naive "Transistor Assisted" ignition circuit, it does offer the benefit of less erosion on the spark plug points, much greater immunity to HT leakage current issues and a more powerful spark to allow improved fuel economy and engine performance. If you're going to start adding additional electronic parts (points of failure) to the basic ignition circuit, you may as well "Be hung for a sheep as for a lamb". :-)
I'd guess what is actually hidden away under that plastic cover rather depends on the vintage of that B&S engine. If it's using 21st century technology, there's every chance there's a transistor or 3 involved. Earlier than that and it's likely to just consist of nothing more sophisticated than a set of CB points and a 500v 100nF capacitor.
If it's using 21st century technology, the two most common ways, aside from a mechanical CB points set, were either magnetic or optical triggering. Since optical triggering was popular on aftermarket transistorised ignition upgrade kits for 20th century motorcars, the most likely choice for 'by design' ignition systems built into the later electronically ignited petrol engines was 'magnetic' triggering which may be nothing more than a sensing coil embedded into that plastic cover with a tiny triggering magnet embedded into the flywheel (although the generator magnets *could* be used for this function, a seperate tiny magnet offers more precise timing - this may even simply be an extra bit of iron to divert a fraction of the magnetic flux from one of the generator magnets rather than an actual seperate tiny magnet).
Careful probing with a small steel rod might reveal the presence of such a triggering magnetic field 'hot spot' on the inside of the outer rim of the flywheel. If such a 'hot spot' is detected, you have your answer as to why there's no sign of a contact breaker.
With regard to testing the sparking efficacy of the ignition system, you really need to use an air gap of at least quarter of an inch, preferably a 10mm spark gap at standard atmospheric pressure. The breakdown voltage per millimetre is roughly proportional to pressure.
The voltage required to jump the the typical 0.8 to 1.00 mm spark plug gap is only a tenth or less than that needed in actual service. BTW, if the handbook specifies somewhere close to a 1.5mm gap, you can be reasonably be sure of the use of a CDI module.
A simple high voltage power transistor switch substitute for the less elegant electronic version of the Kettering CB points arrangement as used by the Suzuki GSF600 digital ignitor module - a microprocessor controlled ignition module let down by the weird choice of electronic CB points over the technologically correct CDI system - I was *so very not impressed!*, is just as prone to HT leakage current issues as the traditional CB/ condensor/ignition coil system of yester-millenium.
If you have a spare sacrificial spark plug to hand, you can bend the earth electrode away from the tip to regap it out to 7 or 8 mm purely for use as a spark gap tester for ignition systems in general (attach the HT lead and rest the plug body on any handy metalwork electrically bonded to the engine if not the engine itself).
Also, a handy insulator such as a piece of thin paxolin or perspex sheet which can be gently wedged in the spark plug gap to force the spark to bend around the obstruction for a total spark path length of circa 8 to
10 mm is a non destructive way to check the actual spark plug's insulation performance after removing it from the engine and letting it rest in contact with the engine as previously suggested for the test spark gap plug.
The point is that even a failing ignition system can easily produce sparks in open air over a 1mm gap leaving you to try and judge the quality by intensity of the spark alone. Testing with a circa 8 to 10 mm gap removes such uncertainty from out of the equation.
Woodruff Key that holds the fly-wheel in place. They're made of a soft(ish) alloy and can become partially sheared through rotor blade impact. This throws out the timing with regards to peak voltage generation.
You'll need to make up a DIY flywheel puller with some steel plate with holes drilled to align withthe holes on the flywheel which may require a thread tapping into them if it's never been removed before.
Think I still have the puller I knocked up in my apprenticeship years. If you need to see a picture I'll try and find it.
You can't get the flywheel off without one if the key is damaged and typically the vast majority I ever had dealings with were.
It's a common fault and the B&S service kit had a replacement with the points and condenser.
Mind you, it's 30 years ago since I was doing that stuff so I forgive any errors in my advice. :)
Yes. Probably something as simple as this (you may have better info in the manual you mentioned):
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;-)
No, it may not (unless your motorcycle uses the same system). ;-)
The thing most people consider a coil is a cylindrical object with an HT lead (or connector) poking out the end and a couple of screw or spade terminals (one to ignition or ballast resistor and the other to points or electronic equiv).
My MZ had what I think you would recognise as 'a coil' but the BMW one(s) was something between that and what you may be seeing on the B&S engine.
If you imagine a magnet built into the outside of the flywheel, these coils are normally wound on a 'square U' shaped iron lamination where the ends of the laminations face the flywheel and are shaped (concave) to match the circumference of the flywheel. As the flywheel rotates the magnet passes across the ends of the ignition coil core, magnetic flux passes though the iron and generates a current in the coil windings. I'm guessing it may do the same as the flux collapses and if so I'm not sure which end of the process generates the spark that's used (it doesn't matter as the flywheel is keyed to the shaft and the coil only adjustable re it's distance from the flywheel). ;-)
FWIW, for setting that gap I've seen suggestion of passing a couple of sheets of paper between the coil and the flywheel and with the two screws loosened, gently hold the coil against the paper / flywheel and nip up the screws. Rotate the flywheel with the paper and then check there is clearance throughout a complete revolution. If the flywheel isn't completely circular, do this at the highest point or if you do it where the magnet is, you won't have to apply any effort to hold it in place. ;-)
It is possible the could could be set with too large a gap (see the manual for the spec on that) and it will make a big difference (especially if the system is marginal).
replying to wasaol, Roj wrote: Hi where can I get the manual from? When I search the Briggs and Stratton website for my model number it just draws a blank. Cheers
My experience when looking for information on the B&S web site was that you have to be quite 'inventive' with the model number to find the relevant information. If I remember right for my B&S engine one had to prefix the model number (as shown on the engine) with a zero.
However the B&S engine 'manuals' are fairly minimal and are really only tell you how to do fairly trivial things like change oil, lay up for winter, etc.
There is a gasket that seems to fail regularly in the carb and the magneto thingy also fails too often. Check for a spark first, before wasting any time.
It?s so obvious that if I need to explain how I suspect you wouldn?t understand. Not that it matters what I say because as usual, rather than start a new thread you?ve tagged on to an old one and unless you search old messages, you won?t see this.
Drain petrol into a glass jar, let it settle for half and hour. If you see it separate into two parts then likely you are trying to start it with water! Also check any petrol you have in a can. Shake it up first and pour off a glass jars worth.
Also don't use any old (6 to 12months) petrol unless perhaps you have added a fuel stabiliser additive
My B&S powered tractor is like that. I can just about heave it on my own, onto its side to work underneath it. Tip it the wrong way and sump oil floods into the carb. and the air filter. It has to be tipped carb. side uppermost, but I have never seen an instruction to do that.
Perhaps I run better/better maintained engines, but I have never had a problem with old fuel. My tractor sits with fuel in it all winter and always starts first turn of the key.
I believe the problem may be with fuel (petrol) with a higher ethanol content which can "pull" water out of the atmosphere. I have previously had problems with the water content in a plastic can of fuel kept outside for a year
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