I remember the first time I tried to tune up my old Stihl MS310. The manual was… well, it was a manual. Lots of diagrams, lots of warnings, and a confusing section on carb adjustment. I kept thinking, ‘Are the adjustment screws on Stihl MS310 pre set?’ because I didn’t want to mess up a good thing. I’d heard horror stories about people ruining their chainsaws by fiddling with the wrong screws. This article is my no-nonsense take on what you need to know.
Frankly, most guys I know just grab their saw, yank the cord, and hope for the best. But if you’ve ever dealt with a sputtering, bogging-down saw that just won’t run right, you know that’s not a plan. You’ve got to understand the carb adjustments, even if you’re just trying to figure out if they’re supposed to be left alone from the factory.
The Truth About Factory Settings: Are They Really ‘pre Set’?
Let’s cut to the chase: when a Stihl MS310 rolls off the assembly line, its carburetor adjustment screws are indeed set to a factory baseline. That’s the ‘pre set’ part. They’re not just randomly screwed in; they’re calibrated to a specific air-fuel mixture that should, in theory, allow the saw to run properly under standard conditions.
Think of it as a starting point. Stihl, like most manufacturers, aims for a general-purpose setting that works reasonably well across a range of altitudes and temperatures, without requiring immediate user intervention.
These settings are typically found on the carburetor itself, usually marked with an ‘L’ for low-speed and an ‘H’ for high-speed circuit. There might also be a throttle stop or idle speed screw (often just called ‘T’ or ‘S’ on older carbs, or a separate idle screw on newer ones). The idea is that the saw should start, idle, and accelerate without stalling right out of the box.
However, and this is where the ‘pre set’ concept gets fuzzy, this factory setting is a compromise. It has to account for variations in fuel quality, atmospheric pressure, and temperature. What runs perfectly at sea level in cool, humid air might run lean and hot at 5,000 feet on a dry, summer afternoon. This is why you see so many discussions about tuning.
It’s not that the screws are wrong, it’s that they’re general. A saw that’s been sitting on a shelf for a year, or one that’s seen heavy use and accumulated some carbon, might need a slight tweak to bring it back into optimal running condition. I learned this the hard way. I bought a used MS310 once, and it ran okay, but it always felt a little gutless and would bog down if I gave it too much throttle too quickly.
I assumed it was just an older saw, but a quick carb adjustment transformed it. That initial ‘pre set’ was likely for a different environment or had drifted over time.
The common advice you’ll find online often tells you to just leave them alone unless the saw is misbehaving. That’s not bad advice, but it’s incomplete. If you’re experiencing issues like poor acceleration, stalling, overheating, or excessive smoking, then yes, the ‘pre set’ might be the problem. The key is understanding what those screws do and how to adjust them safely. You’re not just randomly turning screws; you’re fine-tuning the fuel delivery based on how the saw is actually running. So, while they are pre-set, don’t treat that setting as gospel. It’s a starting point for a machine that, ideally, needs to be adapted to its working environment and its current condition.
Decoding the Carburetor: What Those Screws Actually Control
Alright, let’s get down to the nitty-gritty of those little screws on the carburetor of your Stihl MS310. Understanding what they do is half the battle, and honestly, it’s not rocket science. You’ve got your Low-speed (L) and High-speed (H) adjustment screws.
The ‘L’ screw primarily controls the fuel mixture at idle and up to about quarter throttle. It dictates how much fuel gets mixed with air when the engine is just ticking over or when you’re gently applying throttle. If this screw is set too lean (too little fuel), the engine might hesitate, sputter, or even die when you try to accelerate. Too rich (too much fuel), and it might run rough, smoke excessively, or have a sluggish response.
The ‘H’ screw, on the other hand, takes over from about half throttle to wide-open throttle (WOT). This is where the saw is doing its real work, cutting through wood.
If the ‘H’ screw is too lean, the engine can overheat, lose power at high RPMs, and in extreme cases, seize up – which is a catastrophic and expensive failure. Too rich on the ‘H’ circuit, and you’ll likely notice a lack of power, excessive smoke, and the saw might not reach its full potential speed.
Then there’s the idle speed screw. This one is often overlooked or confused with the ‘L’ screw. The idle speed screw doesn’t directly control the fuel mixture; instead, it adjusts the throttle plate’s position, dictating how open the carburetor is at idle. This determines how fast the engine idles. (See Also: Are The Aluminum Pillars Supposed To Touch The Action Screws )
You want it high enough so the engine doesn’t stall when you let off the throttle, but not so high that the chain starts spinning on its own, which is a major safety hazard. Getting the idle speed right is important for a smooth transition between idle and acceleration. A common mistake is to crank up the idle speed screw to compensate for a lean L-circuit, which is a band-aid fix and can cause other problems.
The key takeaway here is that these aren’t just on/off switches. They are infinitely variable dials that, when properly adjusted, create a smooth, powerful, and reliable engine performance. They work in conjunction with each other and with the engine’s demands. Think of it like tuning a guitar – you’re not just tightening one string randomly; you’re adjusting each one to create a harmonious sound. For the MS310, a well-tuned carburetor means more power, better fuel economy, and a longer engine life. The factory settings are a starting point, but understanding these components lets you fine-tune your saw for the specific conditions you’re operating in.
Why a ‘pre Set’ Carburetor Might Not Be Enough: Altitude and Fuel Factors
This is where the rubber meets the road, or rather, where the saw meets the wood. The factory settings on your Stihl MS310 are designed for a theoretical ‘average’ operating condition.
But ‘average’ rarely exists in the real world. Two of the biggest culprits that make those ‘pre set’ screws less than ideal are altitude and fuel. Let’s start with altitude.
Air is thinner the higher up you go. Thinner air means less oxygen. Your engine needs a specific ratio of fuel to oxygen to run efficiently. If you take a saw set for sea level (richer mixture needed) up to, say, 5,000 feet, it’s effectively running with too much fuel and not enough air – it’s too rich.
This can lead to a sluggish engine, fouled spark plugs, and poor performance. Conversely, if you live at high altitude and your saw was already tuned for it, taking it down to sea level would make it too lean. Lean conditions at lower altitudes mean higher operating temperatures, increased risk of overheating, and potential engine damage.
I once borrowed a buddy’s saw that was set up for the mountains, and took it to my place near the coast. It ran like a scalded dog for about ten minutes, then started to bog down and get incredibly hot. I thought I’d killed it, but a quick carb adjustment (enriching both L and H circuits) saved the day.
Fuel quality is another major factor. The ethanol content in gasoline varies wildly depending on your region and the specific pump. Ethanol absorbs moisture and can cause corrosion in fuel lines and carburetors.
More importantly for tuning, it burns differently than pure gasoline. While modern carburetors are designed to handle some ethanol, the ‘pre set’ values might not be optimal for the specific blend you’re using. Sometimes, you might find that a slightly richer mixture than factory spec runs better with your local fuel.
Also, don’t underestimate the age of your fuel. Stale gas can lead to poor combustion and make tuning more difficult. Always use fresh fuel, ideally with a lower ethanol content if available.
These environmental factors – altitude, temperature, humidity, and fuel type – are precisely why a ‘pre set’ carburetor isn’t the final word. It’s a starting point, and a skilled user will adjust it to match the conditions. Ignoring these factors is a common mistake and often leads people to believe their saw is inherently flawed, when in reality, it just needs a simple tuning for its operating environment.
This is why learning to tune is more than just a good idea; it’s a practical necessity for any serious chainsaw user.
Real-World Tuning: What to Look for and How to Do It
Okay, so you’ve accepted that those ‘pre set’ screws might need a little coaxing. How do you actually do it without turning your powerful MS310 into an expensive paperweight? First, you need the right tools. Typically, a small flathead screwdriver or a specialized carburetor adjustment tool (often called a Z-tool or spline tool, depending on the carb type) is required. You’ll also need a tachometer if you want to be precise with the idle speed, but you can get by with a good ear and a feel for the engine. Start the saw and let it warm up for a few minutes. Cold engines don’t tune well. (See Also: Are Black Screws Rust Resistant )
The process usually involves these steps:
- Idle Speed Adjustment: Make sure the saw idles smoothly without stalling. If it’s too low, the chain might creep or the saw will die when you let off the throttle. Turn the idle speed screw clockwise to increase idle speed, counter-clockwise to decrease it. Aim for a speed where the chain just doesn’t move.
- Low-Speed (L) Circuit Tuning: With the saw idling, gently squeeze the throttle. Listen for how it responds. If it hesitates, sputters, or dies, the L-screw is likely too lean. Slowly turn the L-screw counter-clockwise (richer) a quarter turn at a time, testing the throttle response after each adjustment. You’re looking for the point where the engine accelerates cleanly and smoothly without hesitation. Be careful not to go too far; a bogging sound when you blip the throttle can indicate it’s too rich. Many people don’t realize that the L screw also affects the transition to the H circuit.
- High-Speed (H) Circuit Tuning: Once you have a good idle and acceleration, it’s time for wide-open throttle (WOT). Find a comfortable position where you can safely run the saw at full throttle (e.g., in a log). You’re listening for the engine’s tone. Ideally, at WOT, the engine should sound like it’s revving freely and powerfully. If it sounds like it’s struggling, ‘four-stroking’ (a choppy, uneven sound), or losing power, it’s likely too rich. Turn the H-screw clockwise (leaner) a quarter turn at a time. If it sounds thin, sharp, or like it’s about to seize (a high-pitched scream), it’s too lean. Turn the H-screw counter-clockwise (richer). The sweet spot is usually a clean, strong sound without the over-revving or struggling noises. Some sources suggest finding the leanest setting that allows the engine to reach max RPM without a noticeable bog, then backing it out a quarter turn for safety.
- Re-check Idle and Transition: After adjusting the H circuit, go back and re-check your idle speed and the transition from idle to throttle. Adjustments to one circuit can slightly affect the other.
It takes practice. I remember my first few attempts took me nearly an hour. Now, I can get a saw running sweet in about fifteen minutes. The key is to make small adjustments, test, and listen. Don’t be afraid to experiment within reason. If you go too far, you can always go back to your starting point or even reset them to a known good setting (often 1.5 turns out for both L and H is a common starting point if you’ve really messed things up).
Common Mistakes and Why You Might Be Making Them
Look, messing up carb adjustments is incredibly easy, especially when you’re starting out. The biggest mistake I see people make is trying to tune a cold engine.
Chainsaws, like most small engines, need to be at operating temperature for the fuel mixture to stabilize and for you to get an accurate reading of how it’s running. Trying to tune a cold MS310 is like trying to judge a car’s MPG on a cold start – it’s not representative. Another massive blunder is not understanding the difference between the idle speed screw and the low-speed (L) mixture screw. People often crank up the idle speed to compensate for a hesitation off idle, thinking they’re fixing the mixture.
All they’re doing is making the saw run faster when it shouldn’t, potentially leading to a spinning chain when you least expect it. This is a serious safety issue.
Then there’s the ‘too rich’ versus ‘too lean’ confusion. People hear ‘rich’ and think ‘more power,’ or ‘lean’ and think ‘faster.’
It’s not that simple. Too rich makes the engine load up, smoke, and run poorly.
Too lean makes it run hot, lose power at the top end, and can lead to catastrophic engine failure. I’ve seen guys lean out their saws to the point where they sound like they’re screaming at WOT, only to have them seize up a few minutes later.
That’s not a tuned saw; that’s a ticking time bomb. Another common pitfall is making too large of an adjustment at once. If you turn the screw a full turn when it only needed an eighth, you’ve likely overshot the mark and now you’re chasing your tail.
Small, incremental adjustments are the way to go. Finally, some folks just don’t listen. They make an adjustment, get impatient, and rev the saw, expecting an instant change.
You need to give the engine a moment to react to the adjustment.
One contrarian opinion I often hear is that you should never touch the factory settings. I disagree, vehemently. While the factory settings are a baseline, they are a compromise. If you’re running your saw in conditions significantly different from where it was calibrated, or if the saw has accumulated wear, those settings are no longer optimal. Ignoring them means you’re leaving performance on the table, potentially shortening the life of your saw, and even compromising safety. The MS310 is a solid saw, but it’s not invincible. Proper tuning makes sure it runs reliably and safely for years. Don’t be afraid of the screws; learn to use them responsibly.
When to Actually Worry: Signs Your Ms310 Needs More Than Just Tuning
So, you’ve tinkered with the L and H screws, you’ve set the idle, and your Stihl MS310 still isn’t running right. What then? It’s time to consider that maybe the problem isn’t just a misadjusted carburetor. (See Also: Are Blue Concrete Screws Waterproof )
One of the most common culprits is a dirty or clogged air filter. A restricted air filter chokes the engine, making it run rich, bog down, and lose power – symptoms that can mimic a poorly tuned carb. If you haven’t cleaned or replaced your air filter in a while, do that first.
It’s simple, cheap, and often solves a host of running issues. Another thing to check is the spark plug. Is it fouled, worn out, or damaged?
A bad spark plug can cause misfires, hard starting, and poor performance. Replace it if it looks questionable.
The fuel system itself can be the issue. A clogged fuel filter, a kinked fuel line, or even water in your fuel can cause problems. If you’ve used old gas or suspect contamination, drain the tank and refill with fresh fuel. The carburetor itself might also be internally dirty or damaged. Gunk from stale fuel can clog the tiny passages inside. If cleaning the external adjustments doesn’t help, a full carburetor rebuild or replacement might be necessary. This involves taking the carb apart, cleaning every nook and cranny with carb cleaner, and replacing any worn gaskets or diaphragms. It’s a bit more involved than just turning screws, but often brings an old saw back to life.
Don’t forget about the exhaust system. A clogged muffler or spark arrestor screen can significantly reduce engine power and cause it to overheat. Removing and cleaning the spark arrestor screen is usually straightforward and can make a noticeable difference. Finally, consider compression.
If your MS310 has low compression, no amount of carb tuning will make it run powerfully. This usually indicates worn piston rings or cylinder damage, which are more serious mechanical issues. You can check compression with a simple compression tester. If you’ve gone through all these checks and the saw still runs poorly, it’s time to either consult a professional mechanic or consider whether the cost of repairs is worth it for an older saw.
But before you get to that point, make sure you’ve exhausted the simple tuning and maintenance steps.
Frequently Asked Questions About Stihl Ms310 Carburetor Adjustment
Are the Adjustment Screws on Stihl Ms310 Pre Set?
Yes, the adjustment screws on a Stihl MS310 carburetor are indeed ‘pre set’ to a factory baseline setting from the manufacturer. This factory setting is intended to allow the saw to run acceptably under general operating conditions out of the box. However, it is a compromise and may not be optimal for your specific altitude, temperature, fuel, or the saw’s current condition, often requiring fine-tuning.
How Many Turns Out Should the L and H Screws Be on a Stihl Ms310?
While there’s no single universal answer because it depends on conditions, a common starting point if you need to reset your Stihl MS310 carburetor screws is to turn them both in gently until seated, then back them out approximately 1.5 turns. This is just a baseline, and proper tuning involves adjusting them based on the saw’s performance, listening to the engine’s sound, and observing its response. Always make small adjustments and test.
Can I Adjust the Carburetor on My Stihl Ms310 Without a Tachometer?
Yes, you can adjust the carburetor on your Stihl MS310 without a tachometer, although a tachometer offers greater precision for setting the idle speed. For the low-speed (L) and high-speed (H) circuits, you primarily rely on listening to the engine’s sound and observing its acceleration and full-throttle performance. You can achieve a good tune by ear and feel, focusing on smooth acceleration and a strong, clean sound at wide-open throttle. Setting the idle speed can be done by ear to prevent stalling and make sure the chain doesn’t engage.
| Component | Function | Adjustment Type | Impact of Lean | Impact of Rich | My Verdict |
|---|---|---|---|---|---|
| Low-Speed (L) Screw | Idle to 1/4 throttle fuel mixture | Screw (L) | Hesitation, stalling, bogging on acceleration | Rough idle, excessive smoke, poor throttle response | Important for smooth take-off. Easy to get wrong. |
| High-Speed (H) Screw | 1/2 to Wide Open Throttle (WOT) fuel mixture | Screw (H) | Engine overheating, loss of power at WOT, potential seizure | Engine lacks power, sounds ‘chuggy’ or ‘four-stroking’ | Most important for power and engine survival. Get this right! |
| Idle Speed Screw | Engine RPM at idle | Screw (T/S or separate idle screw) | Stalling when throttle released, poor transition | Chain engages at idle (safety hazard), wastes fuel | Key for safety and usability. Don’t ignore this. |
Conclusion
So, to circle back to the main question: are the adjustment screws on Stihl MS310 pre set? Yes, they are, but that’s just the starting point. Think of them like the factory settings on your car radio – they’re okay, but you’ll probably want to dial in your favorite stations. Altitude, fuel quality, and the wear and tear on your saw all mean that those initial ‘pre set’ values might not be doing your saw any favors. Learning to adjust them properly, even with just your ears, can make a world of difference in performance and longevity.
Don’t be intimidated by the carburetor. It’s not some mystical black box. It’s a mechanical device designed to be tuned. If your saw is running rough, bogging down, or just not performing like it used to, don’t immediately blame the saw itself. More often than not, a simple carb adjustment is all it needs. Take the time to understand what those screws do, make small, careful adjustments, and listen to your engine. It’ll thank you with more power and a longer life.
If you’ve tried tuning and it’s still not right, remember to check the basics: air filter, spark plug, and fuel quality. Those are often the real culprits behind poor performance, and they’re even easier to fix than carburetor screws.
