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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:
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.
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!
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 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 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.
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.
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.
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
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.
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.
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
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.
Copyright 2002 - David Coker / D.C. Web Enterprises - All Rights Reserved