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The Fuel System

Problems related to the fuel system are extremely common and can easily rank as the #1 cause for jobs seen in the shop simply because of the high number of potential failures that can occur. More parts, more pieces, more problems!

Even if you don't feel comfortable with the thought of servicing that tiny carburetor (clean or rebuild), there are still many simple things that you can do that may in fact correct a given problem! Below we will explore those options:


Air Filter
The air filter is absolutely critical when it comes to the performance of 2-stroke engines. They can be compared to the lungs on the human body and are just as important to the health and well being of your engine. Simply put, in order to run and stay running well, your engine (and body) must "breathe".

A dirty air filter will not allow the engine to breathe, resulting in poor performance, hard starting, and fuel fouled spark plugs.

Service options include cleaning or replacement.
 
Fuel Mix
Many problems can be caused by the use of stale fuel and since gasoline has a relatively short storage life (approximately 30 days) you should always make this a consideration when troubleshooting.

*Note - Unless you use your equipment on a daily basis, it's a good idea to mix only smaller quantities of fuel at a time, using the manufacturer's recommended mixing ratio!
 
Fuel Tank
Trash, water and stale fuel all have an adverse impact on your engine, so the fuel tank should be flushed and/or cleaned occasionally. It's also a good idea to check your fuel can on a regular basis as well.
 
Fuel Filter
Fuel filters (located inside the fuel tank) can and eventually do become clogged up with whatever happens to enter the tank besides fuel mix. Stopped up fuel filters won't allow enough fuel (if any) to reach the carb, causing a "too lean" running condition at best.

The only recommended service option is replacement.

*Note- Fishing the filter out of the tank can be accomplished using a simple tool constructed out of a stiff wire or coat hanger.
 
Fuel Hoses
Fuel hoses are obviously important. They can become hard and brittle with the potential to develop either fuel or air leaks. Sometimes the hose that attaches to the fuel filter inside the tank will become soft and collapse, not allowing fuel to travel to the carb.

Service to fuel hoses should include inspection and/or replacement as required.
 
Impulse Hose
Low end compression is also often routed either through a "port" or by means of a small hose, into a passage located in the carburetor. This is the "impulse" that drives the diaphragm pump in the carb.

If your engine is equipped with an impulse hose, service should include inspection and/or replacement as required.
 
Carburetor Service
Service to the carburetor usually involves a thorough cleaning and/or a complete rebuild using new parts, along with final adjustments as required.

Unfortunately, offering instruction in this area is well beyond the scope of this guide.
 
Adjustments
If your engine has an adjustable carb, periodic adjustments may be required. Older versions will usually have 3 adjustment screws, while the newer E.P.A. approved versions may have only two or less! Below I've displayed an older style carb so that we will have a point of reference for all three styles.

 
A - Main idle adjustment screw
B - Low side adjustment screw (usually stamped 'L")
C - High side adjustment screw (usually stamped 'H")
 
 
 
 

Although the general style of the carb shown is the most common type in use (adjustable or not), don't be too alarmed if you find that your carb looks nothing like the one pictured...
 
Basic adjustments should start with the mixture screws (B and/or C) turned out between 1 -1 1/4 turns from a lightly seated position, which will usually allow the engine to start and run. Additional adjustments should be made in increments of no greater than 1/16th of a full turn. For both low and high side screws, turning the screw in (clockwise) will "lean" the mixture and opening the screw (counter-clockwise) will "fatten" or enrich the mixture.
 
Low Side
Adjustments to the low side should made until the engine is capable of running at idle and the lower RPM ranges, yet not so lean that it has an adverse affect on throttle responsiveness. Poor throttle response is usually a sure sign of a "too lean" fuel mixture.
 
High Side
Adjustments to the high side will affect the top RPM speed of the engine. Caution should be taken to make sure that the carb isn't adjusted "too lean", since that can cause a loss of useable power, engine over speeding and possibly severe damage.

Proper adjustment requires the use of a digital tachometer capable of reading 10,000+ RPM's along with the manufacturer's specifications. Adjustments made
without a tachometer should always be made on the "fat" or "rich" side to help avoid potential damage to the engine.
 
Main Idle Screw
The main adjustment screw controls the final idle speed for the engine and should be made after the other adjustments.
 

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