The Facts on Today's Pro Saws
Today’s pro saws, and all new hand held power equipment sold in the US, must meet emission specifications set by the Environmental Protection Agency (EPA). We are often asked about these regulations and how they affect pro saw performance. The following are some questions and answers we've compiled on the subject.
Q: What does the EPA regulation do to pro saws?
A: The EPA regulation is complex, but basically it requires manuafacturers to design saws that produce less harmful emissions - less carbon monoxide (CO), less hydrocarbons (HC), and less nitrogen oxide (NOx). The amount each saw model is allowed to emit varies and is based on its power output. Large and powerful pro saws are allowed to produce more emissions than smaller less powerful saws.
This is a Husqvarna 575XP. It is designed using stratified charge technology. New versions of this saw also have a "self-adjusting" electronic carburetor. This is a step closer to what we believe will eventually become electronic fuel injection and more sophisticated "electronic engine management systems."
Q: How do saw manufactures make saws that emit less pollution?
A: One way is for engines to run leaner and for less fuel to be in the air/fuel mixture. This creates some challenges for chain saw manufacturers. Lean running engines tend to be over-revved and operate at higher temperatures. Some manufacturers also fit their saws with catalytic converters. These devices are part of the muffler. They reduce HC emissions by burning fuel that didn't get burned in the combustion chamber in the saw's muffler.
Some of today's pro saws employ engines designed using "stratified charge" technology. In this design, a saw's transfer ports are filled with air or exhaust, while and an air/fuel mixture fills the crankcase. During transfer, the first portion that enters the combustion chamber has no fuel in it. This is the portion that usually leaks out the exhaust port, causing HC output. This is an effective design that reduces HC emissions with minimal impact on the performance of the saw. You will see more saws that employ this porting as new saw models are introduced.
Q: How can lean running saws perform well and last?
A: First, special oil and additives have been incorporated into both Stihl and Husqvarna brand mix oils. These changes provide good lubrication to engines operated at a higher temperatures. They have also made some physical changes to the engines, such as an improved cooling system. This is accomplished by adding larger cooling fins on the cylinder and increasing the number and shape of the fins on the flywheel. As for the problem of over-revving, new ignition systems have been developed to control engine speed.
Q: Do Today's saws still deliver good performance?
A: Yes, engineers at Stihl and Husqvarna have both done a great job of minimizing the impact of emission regulations. In many cases, they have done such a good job that most pro users don’t even notice the difference between older non-compliant models and those we sell today.
Q: Does a user have to do anything different with one of today's saw?
A: For pro users, the biggest consequence of emission regulation is more saw maintenance. Things like dirty air filters, worn carburetor diaphragms, and small air leaks now affect the saw’s performance more than in the past. In many cases, a user will no longer be able to adjust the carburetor to compensate for a slight mechanical problem. Worse, if that problem is not attended to, it may quickly escalate into an expensive repair.
Q: What about operational changes?
A: Pro users have to learn to run today's saws without over-spinning the engine. Carb adjustment no longer limits engine speed as in the past. New rev-limiting ignitions systems help, but even with them, RPMs can go past safe levels. If you limb with a heavy trigger finger, you may be spinning your saw high enough to damage the rod bearing. The end result will be a saw with a shorter working life.
Pro users also need to be more conscious of the engine temperature. Running a slightly dull chain has never been a good idea, but it is even a worse one today. A saw under excess load creates extra heat. Since lean running conditions raises the saw’s initial operating temperature, using a dull chain may cause the temperature to rise to the point that the engine is damaged.
Q: What about running oxygenated fuel?
A: Almost all of today's fuel is oxygenated. It will work fine in your pro saw, however, you need to avoid fuels like E85. This is oxygenated fuel, but has a very high proportion of alcohol. This will not work well in a pro saw. Perhaps future pro saws will be able to run this fuel, but for now, stick with standard oxygenated fuel.
Q: Is it best to use regular or supreme grade fuel?
A: Use only fresh fuel with an octane rating over 90, which is usually "Supreme" grade. This allows a saw engine to produce maximum power, while decreasing the chance of detonation.
Q What kind of mix oil works best?
A: We recommend either Stihl or Husqvarna brand two-cycle engine oil. Oil you may have used in the past may not adequately lubricate saws with the added stress of high RPM and elevated engine temperature brought on by the EPA changes. While other mix oil may be less expensive and perform adequately in some two-cycle engines, chances are it will not do the job in a pro saw.
Our favorite oil is Stihl's "Ultra" mix oil. It is a synthetic oil and has the best lubricating properties we've seen. The internals of saws we have inspected that run a steady diet of this oil along with high-octane fuel look good.
Q: What about the procedure for mixing fuel and oil?
A: We recommend that you mix five gallons or less gas at a time. Also, do not mix more fuel than you can use in six weeks. Some of today’s gasoline does not blend as well with mix oil as it used to and this blending ability usually gets worse as it ages. If you have fuel that has been mixed and stored for a long time, don’t use it.
Q: What about air filters?
A: On today's saws, the air filter needs frequent care. We recommend changing or cleaning the air filter at least once per day. It should be replaced after 100 to 150 hours of use or 30 to 35 days of running time. This is more frequent than nearly every pro user does. We also recommend rotating air filters. Rotated filters are more easily cleaned because they usually don’t become as saturated with debris.
One of our customers who runs a large crew has adopted the filter routine suggested above. The results are clear. After almost a year of practicing better filter hygiene, engine down time is significantly reduced and the working life of his saws have been extended.
Q: What about fuel filters?
A: The fuel filter also needs extra care. Replace it after 30 to 35 days of running time and do it more often if working in rain or heavy moisture. Today's fuel filters do an excellent job of filtering fine particles. This is good in that they keep debris out of the carburetor, but bad because they can quickly plug. When this occurs, it can cause the saw to run lean and seize up.
Q: Why can't pro users remove the plastic limiter caps from the carburetor and run it that way?
A: The carburetor will not stay adjusted without the caps in place. Adjustment needles on today's carburetors no longer have springs to hold them in place. Before you get the idea to remove the caps and run it this way, beware.
Q: Will saw manufacturers be able to meet increasingly lower emission requirements?
A: The EPA is going to require even cleaner running saws in the future. Both Stihl and Husqvarna are making heavy investments in the development of EPA compliant products. Rumor has it a single exhaust analyzer used in Stihl’s U.S. manufacturing operation costs close to a million dollars. They currently have three of them.
Q: Will there ever be a four-cycle pro saw engine?
A: It is doubtful. So far, it is not possible to build a four-cycle engine with the power-to-weight performance of a two-cycle.
Q: Is it possible to make cleaner running two-cycle engines?
A: There are a number of technologies that should make it possible to further clean up emissions on two-cycles. One that is most promising is electronic fuel injection. This has revolutionized the auto and truck industry. When smaller, more durable, and less expensive components are developed, pro saws will have their day. This technology allows for both great performance and super-clean running engines. There are other technologies, too.
The one thing you can count on is us to help you with whatever changes occur. Pro saws are our business. As in the past, we will do our best to give you straight talk on tools that do the job... That’s why we’re the Pro’s Choice.