Combustion 101

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Disclaimer: The information provided should never replace common sense or the recommendations of the OEM.  I do not assume responsibility for the use or misuse of this information.  The information provided is based on my experience working as a full time mechanic, on hundreds of motors over time, reading a lot of manuals, education, and consulting other experienced mechanics along with a number of retired service reps I am friends with.
If I can offer any advice from experience, it would be NOT to try and fix your own motor if you don't have a good understanding of what you're doing.  You need to have the right special tools, reference materials, and most importantly, UNDERSTANDING of what is wrong and how to properly fix this issue.  Most people do more harm then good if just messing around blindly.  The reason why I can do these repairs is I've put in thousands of hours reading, fixing, and practicing.  I learn something new everyday.  I have also gone out and acquired the necessary, CORRECT tools and reference manuals to work on the motors.  These are very important to promote correct operation of the motor.  The idea is to have a reliable motor, not just one that 'kinda runs.'

Index - Click below to Jump to That Section

Internal Combustion Essentials
The Basics, What You Need To Know About Motors

Cooling System
Gearcase Components
Ignition System
Fuel System
Mechanical Components
Trailer 101

Explanation of the basic function of a 2-stroke shot by yours truly.

A brief comparison to carbureted motors vs. direct fuel injection.  Old and new technology.  Great video from the History channel.

Excerpt from the Johnson 10th edition service manual (a great read).  This illustrates the power stroke cycle of a 2-stroke internal combustion engine.  Fuel enters via the intake port, is compressed by the piston, ignited by the spark plug, the expelled/burned gasses via the exhaust port (out the bottom of your motor, underwater).

combustion   2

If still images aren't your learnings style, here is an impressive video of internal combustion with a SEE THROUGH motor.  Note this is a 4-stroke motor, so you'll see the fuel charge come in through the lower intake, a cylinder stroke with no combustion where the exhaust exits the upper orifice, then the cyle starts over; hence the terms 2 vs 4-stroke. 

The reason why 2-strokes emit an odor is you are smelling unburned fuel mix being ejected because both the intake and exhaust ports open simultaniously.  With 4 strokes, there are a lot more parts working to eliminate wasted fuel charge; i.e. better fuel economy, but more weight and a lot more parts to break.  I'd rather pay at the pump than out of pockets for more repairs.

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