HOW A FOUR STROKE ENGINE WORKS
Tuning Section
Reading a Sparkplug
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Remember when reading plugs...
- The "Ground-Strap" = Heat Range
- The "Plug's Base-Ring" = Jetting
- The "Porcelain" = signs of preignition/detonation
Sparkplug Heat Ranges Explained
Electrical Section
How Coils and Points operate
As electricity flows through the coil it creates a magnetic field. When the coil TURNS OFF the magnetic field collapses, causing the energy to flow towards the spark plug and causes the "SPARK" needed to run your engine.
Many people think your sparkplug fires when the coil turns on, and this is not true.
If you have problems with lack of spark, begin by testing battery voltage. You generally need at least 10 volts to operate a 3 ohm coil. Test for voltage at the coil. If you do not have proper voltage, trace back toward the engine using a volt meter to find the problem.
If you have proper voltage at the coil, the check for voltage at the points. Think of your contact points (or electronic trigger) as a light switch that operates the coil.
Not shown in the picture is a condenser. The function is to absorb the shock caused when the points open (and turn off the coil). A condenser acts as an electrical sponge. If everything tests good and you still cannot get spark at the coil, you should test or replace the condenser.
Many people think your sparkplug fires when the coil turns on, and this is not true.
If you have problems with lack of spark, begin by testing battery voltage. You generally need at least 10 volts to operate a 3 ohm coil. Test for voltage at the coil. If you do not have proper voltage, trace back toward the engine using a volt meter to find the problem.
If you have proper voltage at the coil, the check for voltage at the points. Think of your contact points (or electronic trigger) as a light switch that operates the coil.
Not shown in the picture is a condenser. The function is to absorb the shock caused when the points open (and turn off the coil). A condenser acts as an electrical sponge. If everything tests good and you still cannot get spark at the coil, you should test or replace the condenser.
Basic negative ground (earth) head and tail light drawing.
| neg_ground_lighting.pdf |
Using a rotary switch to select timing maps
Basic Wiring for Lights
Carburetor Section
Jetting 101
This photo explains the basic principle of carburetor jets. At idle, your pilot jet meters the correct fuel to keep your engine running correctly. As you open the throttle (twist it more on a cycle) you begin to lift the needle. This allows more fuel to be drawn into the engine. When the needle is completely lifted, the size of the main jet then determines how much fuel flows into your engine.
So making adjustments for a rich or lean running carb at low rpm would involve changing a pilot jet. Correcting mid rpm issues would involve changing the needle (or the height of the needle which usually has adjustable slots), and fixing a high rpm running problem would require main jet changes.
Understanding which jets are used for different rpm ranges will help you over come problems due to a high performance exhaust, aftermarket high flow air filters, or other changes in engine fuel needs (big bore kits, high compression, and even a change in ignition systems). Mikuni and Kehin both have more information on their websites.
So making adjustments for a rich or lean running carb at low rpm would involve changing a pilot jet. Correcting mid rpm issues would involve changing the needle (or the height of the needle which usually has adjustable slots), and fixing a high rpm running problem would require main jet changes.
Understanding which jets are used for different rpm ranges will help you over come problems due to a high performance exhaust, aftermarket high flow air filters, or other changes in engine fuel needs (big bore kits, high compression, and even a change in ignition systems). Mikuni and Kehin both have more information on their websites.
Amal Carburetor Tuning
| amal_guide.pdf |
Mikuni Carburetor Tuning
| mikuni_guide.pdf |
Keihin Carburetor Tuning
| keihin_tuning_guide.pdf |
| keihin_pe_carb.gif |
| keihin_pj_carb.gif |
What is Octane?
The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.
The compression ratio of your engine determines the octane rating of the gas you must use unless you can match the timing. Higher octane fuel burns slower, which can help detonation due to incorrect timing. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel (Unless you can control the ignition timing which is why the C5 ignition works so well). The advantage of a high compression ratio is that it gives your engine a higher horsepower rating and usually is a lesser expensive option than running a turbo, supercharger, or nitrous. This is especially true for a street driven vehicle.
The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, methane, propane and butane are all hydrocarbons. Methane has a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.
Heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot with little effect. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent Heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.
The compression ratio of your engine determines the octane rating of the gas you must use unless you can match the timing. Higher octane fuel burns slower, which can help detonation due to incorrect timing. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel (Unless you can control the ignition timing which is why the C5 ignition works so well). The advantage of a high compression ratio is that it gives your engine a higher horsepower rating and usually is a lesser expensive option than running a turbo, supercharger, or nitrous. This is especially true for a street driven vehicle.
The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, methane, propane and butane are all hydrocarbons. Methane has a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.
Heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot with little effect. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent Heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.
Miscellaneous Items
Tired of spending $5 a can for penetrating oil that doesn't work?
Check out this report...
Penetrating oils ........... Average torque load to loosen
No Oil used ................... 516 pounds
WD-40 ..................... ... 238 pounds
PB Blaster .................... 214 pounds
Liquid Wrench ...............127 pounds
Kano Kroil .................... 106 pounds
ATF*-Acetone mix............53 pounds
The ATF-Acetone mix is a "home brew" mix of 50 - 50 automatic transmission fluid and acetone. Note this "home brew" released bolts better than any commercial product in this one particular test.
ATF-Acetone mix is best, but you can also use ATF and lacquer thinner in a 50-50 mix.
*ATF=Automatic Transmission Fluid.
Check out this report...
Penetrating oils ........... Average torque load to loosen
No Oil used ................... 516 pounds
WD-40 ..................... ... 238 pounds
PB Blaster .................... 214 pounds
Liquid Wrench ...............127 pounds
Kano Kroil .................... 106 pounds
ATF*-Acetone mix............53 pounds
The ATF-Acetone mix is a "home brew" mix of 50 - 50 automatic transmission fluid and acetone. Note this "home brew" released bolts better than any commercial product in this one particular test.
ATF-Acetone mix is best, but you can also use ATF and lacquer thinner in a 50-50 mix.
*ATF=Automatic Transmission Fluid.
English to Metric Conversion
Metric Bolt Torque Values
Gearing Chart
This chart explains how changing a front or rear sprocket will change the gearing (and over all performance) of your vehicle.
The simplest way we remember, is the closer your sprockets are to being the same size, the slower it accelerates but the higher the top speed.
Making the sprockets farther from being the same size (smaller front or larger rear sprocket) will generally give you quicker acceleration but decreases the top speed.
The simplest way we remember, is the closer your sprockets are to being the same size, the slower it accelerates but the higher the top speed.
Making the sprockets farther from being the same size (smaller front or larger rear sprocket) will generally give you quicker acceleration but decreases the top speed.
This is a great illustration of a Type B connector...
Type B Crimper Jaws
