Zama vs. Walbro for Stihl MS 170 (Field Test)
There is no universal winner between Zama and Walbro for the Stihl MS 170. The correct carburetor is the one listed for your saw’s exact serial number and carburetor version. Compare brands only when both units are confirmed, calibrated fits. A controlled test can show how they perform; brand names alone cannot predict starting, idle, or cutting power.
A wet carburetor is not a problem that a different brand will fix. Carburetors are not waterproof, and water in fuel can cause hard starting or poor running. If you pulled the cord 30 times, pause before buying parts: identify the carburetor, check fuel and spark, then confirm that any replacement matches the saw.
Equipment Setup, Carburetor Identification & Safety Preparation
This step establishes which carburetor fits and whether the saw is ready for testing. The MS 170 is a 30.1 cc, two-stroke saw, but its parts can vary by production version. A matching brand or similar-looking body is not proof of fit; verify the saw and carburetor identification before ordering.
Confirm the carburetor before comparing brands
Write down the saw’s serial number and the identification stamped on the existing carburetor. Use those details to check the Stihl parts listing or ask a parts supplier to verify the application. Check the carburetor body, fuel connections, throttle linkage, choke linkage, and mounting pattern against the specified part.
Do not assume a Zama or Walbro unit will interchange because it fits the mounting studs. Metering parts, adjustment limits, and linkage can differ. An unverified aftermarket carburetor may also be listed for several saws without being a confirmed match for yours.
Before blaming the carburetor, inspect the basics:
- Check that the fuel is fresh and mixed at 50:1 with approved two-cycle oil. Follow the oil maker’s fuel guidance.
- Check the fuel line and filter for damage, blockage, or loose connections.
- Inspect the air filter and spark plug. A fouled plug or restricted air supply can mimic a carburetor fault.
- Check that the plug lead is connected and test for spark with a suitable spark tester. Keep fuel vapors away from sparks.
- If the engine has spark and fuel but still will not fire, a compression test may help. Use the correct service information to judge the result.
Use the manual’s starting procedure, on stable ground, with the chain brake engaged. Wear eye and face protection, hearing protection, chainsaw chaps, gloves, and protective boots. Keep bystanders clear and check your footing, overhead hazards, and escape route before any cutting.
Check the bar and chain setup
Many MS 170 setups use 3/8-inch Picco low-profile chain in .043-inch gauge, but bar length and drive-link count can vary. Read the bar and chain markings and confirm the parts listing for your saw. Do not assume a .050-inch gauge chain fits a bar made for .043-inch chain.
Use the chain maker’s depth-gauge setting and tool. A 0.018-inch (0.45 mm) setting is a common reference for 3/8-inch low-profile chain, not a substitute for the exact chain specification. A dull, loose, or mismatched chain can make a sound saw feel weak.
Field Cutting Operation and Controlled Zama–Walbro Comparison
A useful field comparison changes only the carburetor. Keep the same saw, bar, chain, fuel, wood, and test steps, then record repeatable results. Without verified fit and service data, a brand-versus-brand run is not a fair test and cannot establish which brand is better.
Use a controlled test, not a guess
I would not call a test a Zama-versus-Walbro result if the carburetors were installed on different saws or tested with different chains. Those changes can affect starting and cutting. Nor should you compare a confirmed OEM part with a unit whose fit or calibration is unknown.
Use a log like this:
| Item | Keep constant or record | Why it matters |
|---|---|---|
| Saw | Same MS 170 and serial number | Avoids differences between saws |
| Carburetor | Make, stamped ID, verified part number | Confirms what was tested |
| Bar and chain | Same bar, chain type, sharpness, and tension | Reduces cutting differences |
| Fuel | Fresh 50:1 mix from the same batch | Reduces fuel as a variable |
| Start test | Cold and warm starts; note method and pulls | Makes starting reports comparable |
| Idle | Note stability and any chain movement | Flags unsafe or incorrect idle |
| Acceleration | Note response and hesitation | Shows how the engine responds to throttle |
| RPM | Record with a tachometer and compare with correct service data | Helps detect under- or over-speed |
A typical published MS 170 reference is about 2,800 rpm at idle and 13,000 rpm maximum no-load. Verify the correct service information for your exact saw before using those figures. Do not alter limiter settings or tune by ear to make one carburetor seem stronger.
For a cutting check, use the same suitable wood and make comparable cuts, without forcing the saw. Keep the bar nose clear of the wood and maintain two-handed control. Stop if the engine surges, hangs at idle, loses power, or seems abnormally hot. These signs can point to a lean condition; continued running can damage the engine.
What a field test can prove
A careful test can show whether a correctly matched carburetor starts reliably, holds a stable idle, responds to throttle, and stays within the applicable RPM specification. It cannot prove that every Zama or Walbro carburetor performs the same way across all MS 170 versions.
If you do not have two verified, correctly calibrated parts and a tachometer, the honest result is “not tested,” not a brand ranking. That saves you from paying for a replacement based on a comparison that does not apply to your saw.
Real-World Installation Scenarios and Results
These examples show how to interpret common repair situations; they are diagnostic scenarios, not measured brand tests. They help separate a fit problem from a fuel or setup problem. The right next step depends on the saw’s part listing and observed symptoms, not on a brand’s reputation.
Scenario: the replacement fits, but the saw will not idle
Suppose a replacement carburetor bolts on, but the engine hunts or the chain moves at idle. Do not keep turning adjustment screws at random. Recheck its application, linkage, intake sealing, and fuel connections. Then have the carburetor checked against the correct service data with a tachometer.
A carburetor that mounts properly can still have the wrong metering setup or adjustment range. If the idle hangs or the saw surges, stop running it until the cause is found. An incorrect or poorly calibrated unit can make the engine run lean and may lead to piston seizure.
Scenario: the saw will not start after fuel sat
If fuel is stale, replacing the carburetor may not solve the problem. Drain and handle fuel as the manual directs, use fresh 50:1 mix, and check the plug, filter, and fuel line. If the exact carburetor is confirmed but the saw still will not run, continue with spark and compression checks before buying another part.
The practical comparison is not “which logo is better?” It is “does this exact part match, and does the saw meet its operating checks after installation?” That question keeps parts spending tied to evidence.
Maintenance, Chain Sharpening & Carburetor Verification
Maintenance removes common causes of poor cutting that can be mistaken for a carburetor fault. Check the chain, bar, air filter, and oil system before judging engine power. After any carburetor work, confirm safe idle and correct RPM using the service information for the saw.
Before cutting, check chain brake operation, throttle lockout, chain catcher, fasteners, chain tension, and lubrication. Bar oil delivery is automatic, but no single flow rate applies in every condition. Confirm oil delivery as described in the manual rather than relying on a universal number.
After cutting, engage the brake, switch off the saw, and let it cool. Clean the cover and air-filter area, then clear the bar groove and oil outlet. Inspect the chain, bar rails, and sprocket. Sharpen the cutters and set depth gauges to the chain maker’s specification.
If you change carburetors, keep the old unit and record both identification numbers. A repeatable return to the original setup can help isolate whether the replacement changed the symptoms. It does not replace correct tuning or a confirmed parts match.
Storage, Fuel Handling & Seasonal Care
Good storage practice helps keep fuel and starting problems from clouding a carburetor comparison. Use fresh fuel mixed at 50:1, store fuel as directed by its maker, and follow the saw manual for storage steps. Do not use brand choice as a substitute for clean fuel and routine inspection.
For a saw that will sit unused, follow Stihl’s instructions for fuel handling and storage rather than relying on a general rule that may not fit your model. Keep the saw clean, protect it from moisture, and inspect the fuel system before returning it to work. If water is suspected in the fuel, address the fuel and system condition; a different carburetor brand is not a waterproof fix.
Bottom Line and FAQ
The best choice is the carburetor verified for your MS 170’s serial number and existing configuration. If both a Zama and Walbro part are confirmed fits, compare them under the same conditions and against the correct service data. Without those controls, there is no reliable field-test winner.
Is Zama or Walbro better for an MS 170?
Neither brand is universally better. Choose the carburetor that Stihl parts data confirms for your saw’s serial number and configuration.
Can I fit a Walbro carburetor where a Zama was installed?
Only if the parts information confirms that exact Walbro unit fits your saw. Similar appearance or mounting holes do not prove interchangeability.
How do I identify the carburetor already on my saw?
Read the identification stamped on the carburetor body, then record the saw’s serial number. Use both to verify the correct replacement in parts data.
Can a new carburetor fix hard starting?
It can if the original carburetor is faulty and the replacement is correct. Check fresh fuel, spark, air filter, fuel lines, and compression before assuming the carburetor is the cause.
What fuel mix does the MS 170 use?
The specified mix is 50:1 gasoline to approved two-cycle oil. Use fresh fuel and follow the oil maker’s fuel-quality guidance.
What RPM should I see?
About 2,800 rpm idle and 13,000 rpm maximum no-load are typical published figures. Confirm the exact service specification for your saw and use a tachometer.
Should I tune the carburetor by ear?
No. Do not tune by ear or alter limiter settings. Check adjustment and engine speed against the correct service data, using a tachometer.
What if the saw surges or hangs at idle after installation?
Stop running it. Verify the carburetor application, intake sealing, fuel lines, filter, and metering setup, then have tuning checked against the correct specification.
Are MS 170 bars and chains all the same?
No. Bar length, drive-link count, and chain gauge can vary. Check the markings and saw-specific parts listing before fitting a bar or chain.
Does the carburetor brand affect bar-oil delivery?
No brand comparison can establish oil delivery. The MS 170 uses automatic bar lubrication; check the oil system and manual instructions independently.
(This article was written by one of our staff writers, Robert Callahan. Visit our Meet the Team page.)
