Question 1

it starts and idles fine but bogs down and almost dies when i touch the throttle to cut.

Accepted Answer

DIAGNOSIS The high-speed circuit in the carburetor is clogged or out of adjustment. It's getting enough fuel for low RPMs but not for the high-speed demand. FIX Start with the carb adjustment screws. With the saw warmed up, slowly turn the high-speed screw (H) counter-clockwise in 1/8-turn increments while gently blipping the throttle. You're listening for a point where it revs up cleanly without hesitation. Don't go more than a full turn out from the baseline setting. IF THAT DIDN'T WORK The fuel filter in the tank might be partially clogged, or the carburetor diaphragm might be stiff and not pumping enough fuel. A carb rebuild kit is the next step. HEADS UP Adjusting the H screw too lean (too far clockwise) will make the saw over-rev and risk serious engine damage from overheating. If it sounds really screamy, turn it back out.

Question 2

my chainsaw won't start at all, not even a sputter, and i just filled it with fresh gas.

Accepted Answer

DIAGNOSIS With fresh fuel ruled out, you're down to spark, compression, or a severe fuel delivery blockage. On these, a fouled spark plug or a dead ignition module are prime suspects. FIX Pull the spark plug. Check if it's wet (flooded) or dry. If it's dry, you're not getting fuel. If it's wet, clean and gap it (0.020 inches) or just replace it—they're cheap. While the plug is out, ground it against the cylinder and pull the starter cord to check for a bright blue spark. No spark means a bad ignition module. IF THAT DIDN'T WORK If you have spark and fuel, check that the on/off switch isn't stuck in the stop position internally. Also, make sure the fuel tank vent isn't blocked, creating a vacuum that prevents fuel flow. HEADS UP Never pull the starter more than 5-6 times with a flooded plug—you'll just hydrolock the engine. Always pull the plug first to check and clear it.

Question 3

the chain keeps coming loose no matter how much i tighten the nuts, like within minutes of cutting.

Accepted Answer

DIAGNOSIS The bar nuts aren't the problem. The bar is likely worn unevenly, or the chain tensioning mechanism (the little pin that engages the bar) is broken or not seated right. FIX With the saw off and cool, loosen the bar nuts. Use the tensioning screw (the one with the plus/minus icon) to adjust the chain until it's snug against the bar but still pulls freely by hand. Now, while holding the bar nose up to keep tension, tighten the front bar nut first, then the rear one. This sequence is key. IF THAT DIDN'T WORK Inspect the bar rails. If they're spread open or unevenly worn, the chain will just rattle loose. Also, check that the tensioning pin inside the housing is actually moving when you turn the screw. HEADS UP A new chain on an old, worn bar will also do this. Bars wear out and need replacement eventually—they're a consumable part.

Question 4

it's getting harder and harder to pull the starter cord on my ms 170, feels really stiff.

Accepted Answer

DIAGNOSIS That's usually a sign of low compression, or the starter mechanism itself is gummed up. On these, the recoil spring can also bind if it's misaligned. FIX First, remove the starter cover and inspect the recoil assembly. Clean out any sawdust or debris. Make sure the spring is seated correctly in its housing. A little light grease on the spring can help. While you're in there, check the condition of the pull cord—if it's frayed, replace it before it snaps. IF THAT DIDN'T WORK The engine might have low compression due to a worn piston or cylinder. You can test this with a compression gauge (should be over 110 psi), but that's a more serious engine issue. HEADS UP Never yank the starter cord out to its full length and let it snap back—that's the fastest way to kill the recoil spring. Always guide it back in gently.

Question 5

saw runs okay but it's throwing way too much bar oil, coating everything in a slick mess.

Accepted Answer

DIAGNOSIS The adjustable bar oil pump is set too high, or oiler plunger (if you have that model) is stuck partially engaged. FIX On the MS 170, there's a small screw on the bottom of the saw, near the clutch cover, that controls the oil pump output. Turning it clockwise (toward the minus sign) reduces oil flow. Start with a quarter-turn reduction, run the saw, and check. You want a light line of oil flung off the chain, not a spray. IF THAT DIDN'T WORK The oil pump itself might be worn or damaged, allowing too much oil past its metering groove. That requires pump replacement. HEADS UP Using thin, non-Stihl bar oil in cold weather can also cause excessive flow because it's less viscous. Always use the proper oil for the temperature.

Question 6

my ms 170 is leaking bar oil really bad, like a puddle under it when it sits, even with the cap tight.

Accepted Answer

DIAGNOSIS Yeah, this one's common. The oil is leaking from the tank vent or a cracked oil line inside the saw. The MS 170's oiling system is gravity-fed, so if it's overfilled or the vent is blocked/open, it'll just drain out. FIX First, only fill the oil tank right before you use the saw, and don't store it full. If it still leaks, check the oil tank vent. It's a small one-way valve. If it's stuck open, oil will seep out. You can try cleaning it, but often it needs replacing. IF THAT DIDN'T WORK The oil feed line that runs from the tank to the pump might have a crack or have come disconnected. You'll need to split the crankcase to get to it, which is a bigger job. HEADS UP Storing the saw on its side, especially on the oil tank side, will make this leak way worse. Always store it upright or on the opposite side.

Question 7

chainsaw starts but the chain won't spin even when i give it throttle, just sits there.

Accepted Answer

DIAGNOSIS The centrifugal clutch is either stuck engaged (rare) or, more likely, the drive sprocket or clutch drum is seized up from lack of lubrication or grime buildup. FIX First, check the obvious: make sure the chain brake is disengaged. If that's not it, remove the side panel and bar. Look at the clutch drum (the sprocket the chain wraps around). Try turning it by hand—it should spin freely when the engine is off. If it's stuck, you need to clean the whole clutch assembly. Gunk from the bar oil and sawdust can glue it solid. IF THAT DIDN'T WORK The clutch springs themselves might be broken or the clutch shoes might be worn out. If the drum spins but the chain still doesn't move when you rev the saw, the clutch isn't engaging. That usually means replacement. HEADS UP Never run the saw without the bar and chain on, trying to 'free' the clutch—you can over-rev and damage the engine. Always do clutch work with the spark plug disconnected.

Question 8

my stihl ms 170 just starts and then dies immediately after a few seconds, won't stay running at all.

Accepted Answer

DIAGNOSIS That's the classic symptom of a clogged or misadjusted carburetor, usually because old fuel gummed up the tiny internal jets. The saw gets enough fuel to start but then starves. FIX First, drain all the old fuel and mix a fresh batch of 50:1 gasoline and Stihl 2-cycle oil. If it still dies, you'll need to clean the carb. Remove the air filter cover and filter, then the carb cover plate. You'll see two adjustment screws: the high-speed screw (H) and the low-speed screw (L). Gently turn both screws clockwise until they lightly seat, then turn each counter-clockwise one full turn out. This is a baseline setting. Reassemble and try starting. IF THAT DIDN'T WORK The fuel filter inside the tank might be completely clogged or the fuel line might have cracked. You'll need to pull the tank apart to check. If you see a little white plastic filter that's brown and gummy, that's your culprit. HEADS UP Don't just crank the adjustment screws wildly—they're very sensitive. A quarter-turn makes a big difference. If cleaning doesn't work, the carb diaphragm might be stiff and the whole carb might need a replacement kit.

STIHL MS 170 Gas Chainsaw

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