School of Agriculture


Natural Resources


Air Cooled Gas Engine Trouble Shooting

Contest Description and Objectives:

This contest will be similar to the small engine contest at the State Fair. The contest will consist of the following parts.

1. A written test on the principles of trouble-shooting gasoline engines.

2. Diagnosing the trouble in an air cooled gas engine that prevents it from starting, smooth operation and maximum power output and then making proper adjustment for its operation.

3. Starting the engine and adjusting it for maximum power in a minimum time using approved skills and orderly procedure.

4. The observance of good workmanship and safety practices through out the contest.

5. Scoring the contestants will be based on systematic approach to trouble shooting, proper use of tools, orderliness and care in handling parts, observance of safety practices, properly adjusted engine at the end of the contest, time used in completing the diagnosis and remedy, quiz on gas engine principles and trouble shooting procedures.

Pre-Contest Preparation:

This Contest will be composed of a written exam section and an engine troubleshooting section. Questions for the written exam portion will stress the theory of engine operation. Suggested preparation for this section would be to study Section 14 of the Briggs and Stratton " Service and Repair Instructions for Single Cylinder 4-Cycle Engines". Questions on the test will include true/false, multiple choice, and short answer. The engine troubleshooting section of the contest will possibly include disassembly, adjustment, and reassembly of the carburetion, ignition, and/or valve assemblies for a Model 80302 Briggs and Stratton engine. Ideal preparation would include familiarity with the service procedures outlined in sections 2, 3, and 6 of the "Single Cylinder Head Repair Manual" BTS Part No. 270962. Proper troubleshooting sequence as outlined in the instructions should be very familiar to the student.
Team Composition:
2 students per team. 3 teams maximum per school.
Contest Rules

1. Contestants must have been enrolled in a course which included instruction on air cooled gas engine operation and servicing.

2. All gas engines are to be inspected by contest officials to assure standard condition and tested for proper performance prior to the installation of malfunctions in the contests.

3. Identical malfunctions will be installed in each engine and they will be checked by the contest committee to assure uniformity.

4. Parts that are needed by the contestants to correct malfunctions will be secured from the judges. Parts should be specifically requested by name by a team member and an adequate reason is to be given for requesting the replacement.

5. Parts damaged through carelessness may, if available, be secured by a team member from the Part Supply designated at the contest. The time taken to install damaged parts will be considered as part of the elapsed time. Damage to an engine which cannot be repaired during the time allowed will result in disqualification from the contest.

6. The judges will observe progress or repairs but will not interfere with teams unless such repairs are damaging to engine or to the safety of the contestants.

7. When the team contestants feel they have finished they will signal the judge and the time will be recorded and the scoring of contestants will be completed by the judge.

8. Each contestant will complete a quiz on their knowledge of gas engine principles and gas engine trouble shooting procedures which will count as 50% of the points in scoring the contest.

9. Contestants are to wear safety glasses in the contest. Each contestant will supply their own glasses.

10. Contestants may assume that the engine is equipped with a functional electronic ignition. There will be no malfunctions requiring the removal of the engine side crankcase cover.

11. A trouble diagnosis guide will be useful in preparing contestants but cannot be referred to during the contest. One sample of such a guide is enclosed but it will not be used as a basis for scoring in the contest.

12. A parts basket will be provided for each team in the contest.

13. Teams will work on a single cylinder 2-4 horse power Briggs & Stratton engine mounted on a bench. Engines will be equipped with either suction feed or float-type carburetors. Engines will be either breaker point or electronic ignition.

14. Teams will be limited to 30 minutes for properly diagnosing and correcting the engine malfunctions.

15. Teams will be given time before the start of the contest to arrange tools on the bench for the contest. The time will not be counted in the contest, but tool arrangements and preparation for the work at hand will be scored.

16. Each team is to provide its own tools for the contest. These should consist of the usual tools which might include sockets, sizes 1/4", 5/16", 7/16" and 1/2" with rachet and 4 - 6" extension; deep wall socket, spark plug wrenches 3/4" and 3/16", a selection of various sized screw drivers and a small hammer or mallet, aluminum, rawhide or plastic faced, plus those tools the teams desire and special tools for Briggs & Stratton servicing such as a feeler gauge (.002" - .025").

Contest Location and Starting Time(s)
10:15 a.m. in Marshal Hall, Room 115


High Team - Certificate
High Individual - Certificate and Scholarship
Second High Individual - Certificate


Air Cooled Gas Engines - Trouble Chart

A. Engine difficult to start

1. No fuel in tank

2. Fuel flow obstructed

3. Loose or defective wiring

4. Spark plug cracked

5. Spark plug fouled

6. Improper choking

7. Improper fuel mixture

8. Throttle valve stuck or out of adjustment

9. Throttle rod loose

10. Defective ignition system

a. Breaker points worn or pitted

b. Breaker points out of adjustment

c. High tension wire shorted

d. Incorrect armature air gap

e. Sheared flywheel key

f. Coil failure

g. Condenser failure

11. Poor compression

B. Engine missing

1. Spark plug fouled

2. Spark plug cracked

3. Defective wiring

4. Ignition or breaker points sticking

5. Spark plug gap wrong

6. Valves warped, broken or sticking

C. Engine losing power

1. Carburetor choke valve partly closed

2. Improper fuel mixture

3. Piston rings sticking

4. Muffler clogged

5. Improper timing

6. Overloaded

7. Cooling air stream obstructed

D. Faulty Carburetion

1. Carburetor improperly adjusted

2. Sediment or water in fuel tank

3. Fuel inlet valve stuck

4. Improper fuel level in carburetor bowl

E. Excessive smoke form exhaust

1. Carburetor needle valve open to far

2. Worn piston or piston rings

F. Explosion in Carburetor

1. Gas mixture to lean

2. Intake valve sticking

3. Intake tappet sticking

4. Intake valve warped or broken

5. Intake tappets set too close

G. Poor Compression

1. Valves not seating

2. Valves sticking

3. Piston rings worn or weak

4. Piston rings broken

5. Piston rings sticking

6. Loose spark plug

7. Cylinder head loose

8. Scored cylinder

9. Worn piston and cylinder

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