Problem 1 : Engine Wont Start Problem  2: Engine Wont Stay Running

So your small engine wont start or wont stay running and it’s making you angry. Mowing your lawn, tilling the garden, blowing leaves cutting wood and blowing snow should not be an infuriating experience.

If you poke around this site enough you will undoubtedly notice that I have a dislike for Ethanol in gasoline (Ethanol E15). E15 fuel is the number one reason for a small engine that wont start, wont stay running. This page is devoted cause and prevention. If you arrived here hoping for a magic fix you might be disappointed. I will say if your small engine wont start or wont stay running you need to either rebuild or replace your carburetor. I encourage you to read the page about my Stihl M55 Cultivator. That is the engine that started me on this troubleshooting quest. I also encourage you to read in detail about why Ethanol is bad for your engine and most likely the reason the engine wont start or stay running. The text below is simply the bottom line with a goal on preventing you from ever experiencing this again.


The alcohol separates from the gasoline. The alcohol is also water soluble. Because of this the alcohol draws and absorbs moisture from the air, a lot of moisture. This gas and alcohol separation combined with absorbed water corrode and clog fuel systems in all 2 and 4 cycle engines.


Today’s gasoline with ethanol has a 30 day shelf life. If you purchase gasoline at your local gas station make certain you follow the recommendations of your engines owners manual. Usually this means buy the highest octane gasoline available. Only by enough fuel to use within 30 days. To limit moisture absorption buy a quality gas can that seals out outside air.

No fuel additive can prevent ethanol E15 gas from going bad and separating.

The Fuel Solution

As stated above use the highest octane gas you can buy and only buy enough gas to last less than thirty days. While that sounds easy it’s unrealistic for a lot of folks and homeowners. The fact that you are reading this page is a confession that you purchase more gas than you can use in under 30 days. I feel there are two far superior methods to deal with this to prevent your engine and fuel system from having issues with Ethanol.


Solution 1 – Instead find a gas station or speed shop that services muscle cars. They will have ethanol free gasoline. Around here we used to have Cam 2 Fuel. I believe Cam 2 Racing Fuel is now Sunoco Racing Fuel. Marina’s and boat yards also may have ethanol free fuel. Fuel without ethanol can last years. These fuel are much more expensive than traditional fuels but the benefit out weighs the cost in my opinion.

Solution 2

Wont Start or Wont stay running

TruFuel Pre-Mixed Engineered Fuel for Outdoor Power Equipment

The nation’s first-ever, ready-to-use packaged fuel engineered specifically for small engines.

TruFuel consists of the highest quality fuel, lubricant and stabilizing components, resulting in optimal equipment performance and long-term engine health. It combines 92+ octane, ethanol-free premium fuel, pure synthetic oil that exceeds test requirements for ISO-L-EGD, API TC and JASO FD and a proprietary additive package that includes an advanced stabilizer and innovative friction modifier.

Each TruFuel package is exclusively engineered to accommodate potential product expansion in varying temperature environments, as well as the rigors of transport, storage and display. The engineered steel sidewalls and dome rigorously are tested and refined to prevent distention failure. The container closure is made from proprietary resin to maximize safety & durability. And there is an optimal container-headspace-to-fuel ratio created for transport/storage stability, even in extreme conditions.

Ethanol Free Gasoline

Ethanol-free means TruFuel will not ruin rubber hoses and plastic components in your small engine, nor attract moisture from the atmosphere and risk engine failure like pump gas and oil, thereby reducing or eliminating costly repairs.


STIHL MOTOMIX PREMIXED FUEL- Patented 50:1 fuel mixture combines non-ethanol, high-octane fuel and premium STIHL HP Ultra oil.

STIHL MotoMix® is our patented premixed fuel, specially blended for ultimate performance. Like a sports drink for your engine, this 50:1 mixture is a combination of premium non-ethanol, high-octane motor fuel and our highest-quality STIHL HP Ultra oil.

Clean and convenient, MotoMix® eliminates the hassle of mixing your own 2-stroke engine fuel while providing superior performance and lubrication. Plus, we stand behind this formulation by doubling the limited warranty when you include MotoMix® with your power tool purchase. STIHL MotoMix® contains no ethanol, allowing it to maintain stability for up to two years after the seal is broken – so it stays fresh in your equipment during long storage periods. MotoMix® is also made of non-aromatic fuel and fully synthetic, highly biodegradable engine oil. It’s no surprise that MotoMix® is the official fuel of the STIHL® TIMBERSPORTS® Series.
Husqvarna XP Pre-Mixed 2-Stroke Fuel-Wont Start or Wont Stay Running

Husqvarna XP Pre-Mixed 2-Stroke Fuel

Husqvarna 50:1 pre-mixed 2-stroke fuel & oil is ethanol free, high octane fuel mixed with Husqvarna’s best synthetic blended oil. Specifically formulated to provide Husqvarna hand held owners with optimal equipment performance. The fuel does not degrade or oxidize like pump gas and stays fresh for years, solving longer term storage issues. It is convenient and ready to use with no mixing required and enables easier and more dependable starts. It also protects the fuel system and saves on carburetors avoiding costly rebuilds and downtime.



 Husqvarna ETHANOL FREE, High Octane Fuel contains a premium High Octane Fuel and Stabilizers. • OCTANE RATING: (R+M)/2 METHOD 95. • This product was specifically formulated to provide the Husqvarna equipment owner optimal performance. • Fuel does not degrade or oxidize like pump gas. • Fuel stays fresh for years solving longer term storage needs. • Easier, more dependable starts. • Protects fuel systems. • Avoids costly rebuilds and downtime. • For use in all Air-Cooled 4-Stroke engines.

HUSQVARNA 4 STROKE FUEL-Wont Start or Wont Stay Running

Lawn Mower Won’t Start, Lawn Mower Won’t Stay Running, Leaf Blower Won’t Start, Leaf Blower Won’t Stay Running, Snow Blower Won’t Start, Snow Blower Won’t Stay Running, String Trimmer Won’t Start, String Trimmer Won’t Stay Running, Chainsaw Won’t Start, Chainsaw Won’t Stay Running, Tractor Won’t StartTractor Won’t Stay Running, Riding Mower Won’t Start, Riding Mower Won’t Stay Running, Generator Won’t Start, Generator Won’t Stay Running, Garden Tiller Won’t Start, Garden Tiller Won’t Stay Running,






STIHL MM55 WONT START WONT STAY RUNNING – A few years back my trusty old MANTIS TILLER died after many years of faithful service. Being the type of person who likes to try new things I decided to switch brands and go with STIHL. Having experienced several years of flawless operation of  a STIHL FS85 STRING TRIMMER I bought the STIHL MM55 with confidence. The MM55 did not disappoint. It was light, powerful and almost fun to use.

As the season ended I winterized the MM55 same as my other 2 stroke equipment. I poured in some gasoline stabilizer and ran the MM55 out of gas. All was good until the following spring. Come April the following year the MM55 turned from joy to nightmare. It wouldn’t start, the primer bulb would stay down after a few pumps. I knew this meant the carburetor had some sort of blockage. I spent a fair amount of time cleaning the carburetor. Still no luck. I could get the M55 running for a few seconds then it would die. Frustrated I brought it to the dealer I bought it from. Two weeks later I got the MM55 back. Cost $85. Diagnosis, blocked carburetor. Solution replaced carburetor. The dealer politely recommended I try a different fuel stabilizer. I figured what the heck.

Fast forward to season end I winterized again with the added step of compressed air at the carburetor inlet. I thought to myself “ok I got it this time”. Well I was wrong. The next spring was the same as the previous. Back to the dealer same thing, $85 and a new carburetor. Yes I was annoyed.  This time at the end of the season a close friend said he could winterize the MM55 and it would be fine. He is a landscaper and he would winterize the MM55 same as all of his Echo power tools. (BTW Mantis uses Echo engine).

Next spring you guessed it, same results. This time I was determined to not only fix the MM55 myself but understand why this tool was so prone to the issue.

STIHL MM55 CARBURETOR 4601-120-0600

STIHL MM55 CARBURETOR 4601-120-0600

STIHL MM55 CARBURETOR 4601-120-0600 – To understand the problem with the MM55 carburetor  was a simple as taking it apart. Turns out that the STIHL MM55 CARBURETOR 4601-120-0600 is not designed in a way that lends to be able to completely remove unwanted fuel. In fact there are two small chambers at the bottom of the STIHL MM55 CARBURETOR 4601-120-0600 that there is no way to remove the fuel other than to take the carburetor apart. Fortunately I had saved all my previous carburetors and upon disassembling I learned they were all corroded in this area. I did not bother to disassemble further but no doubt there is other nooks and crannies that would exhibit the same problem.

Note from STIHL MM55 Website Product Page

Note:  STIHL recommends use of fuel with no more than 10% Ethanol content. Using fuel with greater than 10% Ethanol content may cause damage to your equipment and may void your STIHL warranty

Why does STIHL say this? Ethanol in todays gasoline is the root of the short shelf life of fuel. This is why your STIHL MM55 Wont Start | Wont Stay Running!!!!!!!

Note: Read page 12 of the STIHL MM55 CULTIVATOR Owner Instruction Manual. The manual is available to download or view further down this page!

Fix Your STIHL MM55 Cultivator

So whats the solution for a STIHL MM55 WONT START WONT STAY RUNNING? The easy repair is the head  to your local STIHL dealer and buy a new STIHL MM55 CARBURETOR 4601-120-0600 for about $40. Dont bother buying online. You will end up waiting and paying more. The STIHL MM55 CARBURETOR 4601-120-0600 is incredible easy to replace.

  1. Remove the screw holding the air cleaner together and put the cover and filter off to the side.
  2. Remove the two fuel lines attached to the STIHL MM55 CARBURETOR 4601-120-0600. They just pop off. (In case you forget upon re-assembly the smooth hose is the upper hose.)
  3. Remove the two nuts holding the STIHL MM55 CARBURETOR 4601-120-0600 in place. Leave the gasket on the bolts
  4. Move the throttle lever enough to remove the throttle cable. Pay attention to the little protective sleeves on the cable. They can slide anywhere on the cable. Their proper orientation is to keep the throttle cable from wearing the plastic disc that that the throttle cable wraps around.

Assemble in reverse order. The first time you do this it will probably take 15 minutes. After that 5 minutes. In fact it probably took me just as long to type the 4 steps as it would to perform. The MM55 will start with the second pull.

STIHL MM55 CULTIVATOR Running After Carburetor Change - Video

STIHL MM55 CULTIVATOR Running After Carburetor Change – Video

Click the Buttons Below to Learn Why Your STIHL MM55 CULTIVATOR Has this Problem


Now that I know the problem I have modified my winterizing and storage procedure for the STIHL MM55 Cultivator.

STA-BIL Fuel Stabilizer

STA-BIL Fuel Stabilizer

STA-BIL Fuel Stabilizer – I always include STA-BIL Fuel Stabilizer in my gas. STA-BIL brand Fuel Stabilizer is one of the best products of it’s kind available.

STA-BIL 22001 Fogging Oil

STA-BIL 22001 Fogging Oil

CRC ENGINE STOR | STIHL MM55 Wont Start | Wont Stay Running


Beyond the fuel stabilizer the STIHL MM55 needs one more step. The carburetor needs to have something displace any fuel left in the carburetor and it also needs something to protect and lubricate the internal surfaces. I have decided to treat the MM55 the same as the Mercury outboard of my Ranger Bass Boat which successfully started for 20 plus fishing seasons. I use CRC ENGINE STOR or STA-BIL 22001 Fogging Oil.

After running the STIHL MM55 out of fuel and with the engine off hold the throttle wide open (full throttle) and spray the Engine Stor/Fogging oil in the carburetor and pull the starter rope couple times. This will lubricate the engine cylinder. You can also optionally remove the spark plug and directly spray the Engine Stor/Fogging oil into the cylinder. The next step requires an air compressor. Disconnect both fuel lines from the carburetor and used compressed air to blow the gas out of the engine. I like to hold a paper towel or rag over the carburetor to catch the fuel that blows out of. Be sure to operate the throttle to it’s full open position. Once no more fuel blows from the carburetor fill both ports with the Engine Stor/Fogging oil. Again actuating the throttle. The goal here is to fill the carburetor with the Engine Stor/Fogging oil. Use compressed air on both carburetor ports where the hose was attached. Once complete replace the bottom carburetor hose and one last time fill the top port with Engine Stor/Fogging oil and replace the hose. Place the carburetor in choke mode and with the engine turned off pull the starter rope a few times. You can also press the primer bulb a few times. All this should have saturated the carburetor and engine internals with the Engine Stor/Fogging oil make spring start up a breeze.

Keep in mind upon startup it will take a few pulls to get gas into the system and the MM55 will blow some smoke as the Engine Stor/Fogging oil burn up. also keep in mind that some of the Engine Stor/Fogging oil might leak from the exhaust muffler. Consider that fact during storage.

Solved That!