Stihl MS 151 Easy2Start (Repair Guide)
If your MS 151 C-E Easy2Start will not start, do not keep pulling or buy parts at random. Confirm the exact saw and fitted cutting gear, then check fuel, spark, and compression in order. A wet plug, weak spark, or low compression points to different repairs. Stop if the saw runs hot, surges, or shows signs of piston damage.
“I’ve pulled it 30 times, and now I’m worried I’ve flooded it.” That is a useful clue, not a diagnosis. On this saw, Easy2Start reduces the effort needed to pull the starter; it does not remove the need for the right fuel, a working ignition system, and a sealed engine.
I would begin with safe checks that cost nothing, then test one system at a time. Before ordering parts, read the model and serial information on the saw and check the manual for your market version. The MS 151 C-E is a small, roughly 23.6 cm³ saw rated at about 1.1 kW. Parts and specifications can vary, so confirm them against the saw and its manual.
Confirm the saw and make it safe
These checks establish that you have the right model, a suitable cutting attachment, and a safe starting setup. They also prevent a repair attempt from becoming an injury. Read the manual that matches the saw’s model and market; do not assume a part fits just because it looks similar.
Wear eye and hearing protection, gloves, chainsaw leg protection, and boots. Work on clear, stable ground with people well away. Check the chain brake, throttle lockout, chain catcher, handles, and chain tension. Look over the bar, chain, and sprocket for damage or mismatched parts.
MS 151 C-E setups commonly use a 1/4-inch P pitch and .043-inch (1.1 mm) gauge chain. Those figures are not a substitute for checking the bar stamps and manual. Match the chain’s pitch and gauge to the bar, and verify its drive-link count for that bar. Bar length alone does not prove compatibility.
Use the manual’s cold- or warm-start steps. Keep the saw on stable ground, engage the chain brake, and keep the bar clear. Control the saw as directed by STIHL; do not drop-start it. Easy2Start changes the pull feel, but the correct control position still matters. Once the engine fires, follow the manual’s next step rather than continuing to pull in choke mode.
Diagnose a no-start in order
A no-start means the engine is not running; it does not identify the failed part. I work through fuel, ignition, and compression in that order because simple fuel and plug checks can rule out common causes before more involved testing. Stop if you find damage or a safety fault.
| What you find | What it may indicate | Next check |
|---|---|---|
| Plug wet with fuel | Flooding or failure to ignite | Dry or replace plug as manual allows; check spark |
| Plug dry after starting attempts | Fuel may not be reaching cylinder | Check fuel age, filter, and delivery |
| No spark on a proper tester | Ignition fault or stop-control issue | Check switch, wiring, plug, and coil per service data |
| Weak compression or scoring | Internal wear or seizure | Stop; arrange inspection before running |
Start with fresh, correct premix. The specified ratio is 50:1 gasoline to quality air-cooled two-stroke oil, using the fuel grade and oil required for your version. Never use straight gasoline. If the fuel is old, contaminated, or of unknown mix, drain it safely and use fresh premix. Check that the tank vent, fuel filter, and fuel line are not visibly damaged or blocked; do not poke debris into the carburetor.
Read the spark plug. With the engine off and cool, remove the plug using the correct tool. A wet plug suggests fuel has entered the cylinder, but it does not prove the carburetor is good. A dry plug after repeated correct starting attempts suggests fuel may not be arriving. Check the plug for cracks, heavy deposits, or damage, and use the manual’s specified plug type and gap.
Test spark safely. Use an approved inline or grounded spark tester and follow its instructions. Keep fuel vapors away from sparks, and never hold the plug or lead by hand while cranking. If the tester shows no spark, check the stop switch wiring and connections, plug, and ignition parts using model-specific service data. Do not replace the coil based only on a failed start.
Check for flooding. If the plug is wet, stop using the choke or cold-start setting. Follow STIHL’s manual for clearing a flooded engine; the exact control sequence can vary. Do not repeatedly pull with the plug removed near spilled fuel. Refit the plug correctly, then retry the specified starting procedure once the cylinder is cleared.
Assess compression and air leaks. If fresh fuel and a verified spark do not solve the problem, compression may be low, or the engine may have an intake or fuel-delivery fault. A compression gauge can help, but there is no universal threshold to apply here; use the service specification for this exact version. Piston scoring, a sudden loss of power, unusual heat, or surging calls for stopping the saw and getting the cylinder, fuel system, and intake sealing checked.
Repair the cause, not the symptom
A repair should follow a test result. Replacing a plug, carburetor, or ignition coil without evidence can waste money and leave the real fault in place. Use the parts list for your serial number, and follow the service manual for disassembly and fastener data.
A wet plug with spark may mean flooding, poor fuel quality, or another fault; it is not proof that the carburetor needs replacement. A dry plug points toward fuel delivery, but the filter, line, vent, and carburetor need separate checks. If the plug has no spark on a proper tester, inspect the stop circuit and connections before condemning ignition components.
Two field patterns show why sequence matters:
- Case pattern: wet plug after many pulls. The useful next move is to stop using choke, inspect the plug, and follow the manual’s flooded-engine procedure. Buying a carburetor before checking for spark would not answer whether fuel is igniting.
- Case pattern: starts, then surges and loses power. Treat this as a possible lean-running fault. Stale or incorrect premix, restricted fuel flow, an air leak, or poor carburetor adjustment can damage the piston quickly. Stop running it and have fuel delivery, intake sealing, and carburetion checked.
Do not adjust carburetor screws by guesswork. The correct settings depend on the version and require service data; engine tuning should use a tachometer. Approximate reference figures for this family are 2,800 rpm idle and 10,000 rpm maximum permitted speed, but verify the exact specification before testing. If the chain moves at idle, the engine overspeeds, or it will not idle reliably, stop and repair it rather than changing settings at random. Do not apply generic torque values; fastener specifications vary.
Return the saw to service and maintain it
A successful start is not enough to prove the saw is ready to cut. Confirm that it idles reliably, the chain stays still at idle, the brake works, and the automatic oiling system lubricates the chain. If any check fails, shut it down and repair the fault before cutting.
Use STIHL bar-and-chain oil. There is no single reliable oil-flow rate for every version and operating condition. Check the oil outlet, bar groove, and chain as the manual directs. File the chain using the file size and angles specified for that chain, and set its depth gauges to the chain maker’s specification; do not assume one clearance fits all chains.
For cutting, use two hands, stable footing, and a clear work zone. Keep away from the bar nose and its upper-quadrant kickback zone. Do not cut above shoulder height, make felling cuts, or work aloft without the training and equipment required. The MS 151 is a lightweight pruning and small-diameter saw, not a large-timber felling saw. Suitable wood size depends on the saw setup and the wood, not a universal hardness rating.
After use, stop the engine, let it cool, and clean the filter area, bar groove, oil outlet, and sprocket cover. Store the saw clean and dry, with the chain guarded and away from children. Follow the manual for fuel storage; do not leave unsuitable fuel in the saw. Before using it after storage, recheck the fuel system, chain, brake, and lubrication.
Frequently asked questions
Why does my MS 151 C-E not start after many pulls?
Possible causes include incorrect or stale fuel, flooding, no spark, restricted fuel delivery, or low compression. Check each system in order rather than guessing.
Does Easy2Start mean the saw should start with one pull?
No. Easy2Start reduces the effort needed to pull the starter. The engine still needs correct fuel, spark, compression, and the proper starting procedure.
What fuel mix does the MS 151 C-E use?
The specified mix is 50:1 gasoline to quality air-cooled two-stroke oil. Confirm fuel grade and oil requirements in the manual for your market version.
What does a wet spark plug mean?
It means fuel is present at the plug, often after repeated choke pulls. It does not prove the carburetor is faulty; check spark and follow the manual’s flooded-engine steps.
What chain fits an MS 151 C-E?
Many configurations use 1/4-inch P pitch and .043-inch (1.1 mm) gauge. Confirm the bar markings, drive-link count, and manual before buying a chain.
Can I adjust the carburetor to make it start?
Do not adjust it by guesswork. Incorrect settings can cause poor running or a damaging lean condition. Use model-specific service data and a tachometer, or have a qualified technician tune it.
What if the saw starts but surges or runs hot?
Stop using it. A lean condition from bad fuel, restricted delivery, an air leak, or incorrect adjustment can quickly damage the engine. Have those causes checked before restarting.
When should I stop troubleshooting at home?
Stop if you find piston scoring, low compression, a damaged chain brake, a chain that moves at idle, overspeeding, or a saw that will not idle reliably. These faults need proper service before cutting.
(This article was written by one of our staff writers, Robert Callahan. Visit our Meet the Team page.)
