Carburetor Problems

I prime it and it just dies. Why?

It's frustrating isn't it? You prime the carburetor on the Briggs and Stratton, Tecumseh or other brand engine on your lawnmower or snowblower or other outdoor power equipment and it starts for a few seconds and then dies. Or it doesn't want to rev up unless the choke is half-applied and even then it has no power.  Or maybe it will run, but is constantly surging, revving up and down.

Fortunately, the solution is probably within the abilities of most do-it-yourselfers. Lawnmower repair can be a difficult endeavor. But basic lawnmower repair involves just some basic tools and a good cleaner. A few dollars worth of parts and an hour or two of time and you should be back up and running.

If the engine is hard to turn over, as though the starter just doesn't have the power to crank the engine, then you likely have a different problem. Especially if this is a Briggs OHV engine. For that problem, read the article here.

Your problem is probably nothing more than a stopped up carburetor. If your gas has ethanol in it, and most do, and it has set for more than a couple of weeks, then it's a safe bet that you need a carburetor rebuild. Especially if this engine has set up for any length of time without proper storage.

There are many styles of carburetors out there, literally hundreds, so an article that covers each style is practically impossible. But most four-stroke engines share similar enough carbs that basic cleaning and rebuilding is easily explained.

To begin with, if you have a carburetor on a four stroke engine that doesn't have an external float bowl, but mounts directly to the fuel tank, you can start with removing the tank and carb as an assembly. Be absolutely certain to diagram or even photograph the linkage because there is probably nowhere else you will be able to see how it's put together.

Once you have the tank and carb assembly off, remove the carburetor from the tank and you will see a long pick-up tube and a short pick-up. The long pick-up pulls fuel from the tank and dumps it into an internal-to-the-tank fuel bowl. Look down in the tank and you can see this bowl. These carburetors will use an integral fuel pump, the diaphragm that's between the tank and carb or mounted on the side of the carb behind a metal plate. Remove this and all other gaskets and O-rings. For the small Briggs engines with the plastic carbs, be sure to replace the O-ring on the intake manifold and inspect that manifold for holes.

For these style carburetors, you can usually clean them using nothing more than spray cleaner. The Parts Plus store brand and Berryman's are probably the two best out there. Once you have the carburetor clean, just reassemble the way you took it apart and you're probably good to go. It's a good idea to clean the tank out as well and if there's any rust, it's probably best to replace it.

For the bowl style carbs, follow the same procedure for documenting the linkage, as again, you probably won't find it pictured anywhere. These carburetors work by having the bowl filled by pressurized fuel flow, either from gravity or by a pump. Many of the bowls are held on with a small bolt that has a couple of holes in the side and one in the end. This is your main mixture jet and those holes must be clean.

Disassemble the carburetor completely and remove all gaskets. Cleaning these carbs is more difficult and generally require soaking in a carburetor vat, available from auto parts stores, or ultra-sonic cleaning. You can attempt using spray cans, but be prepared for a less than a 50% success rate. Use a fine wire to chase all holes and reassemble using a new carb kit and follow the enclosed instructions for setting the float. If you pull the bowl off and notice a lot of gray, scaly corrosion, you will probably need to replace the carburetor.

Replace all fuel lines and filters if equipped. Rinse out the tank as well and then replace the carburetor as it came off.

You can help avoid these problems by never leaving fuel in the tank for longer than 3 weeks. The use of a good fuel conditioner, in my shop we use SeaFoam and Techron, will help to eliminate carburetor trouble, but the basic rule of never leaving fuel in the tank still applies. At the end of the season, drain the gas tank and then start the engine and let it run itself out of gas. If you have the SeaFoam or Techron or whichever brand you choose in the fuel, then it will help to protect the carburetor through the off-season.

Parts for most brands are available from your local small engine shop. Or, you can contact an online parts dealer like Most carburetors in this size can be rebuilt for under twenty dollars, not including cleaners. Replacements will run anywhere from twenty or so dollars to well over one hundred. Fortunately, the expensive carburetors are rebuildable almost every time.

So with a little time, and a few tools, you can get that piece of equipment up and running yourself for a fraction of what a shop might charge. Should you run into trouble, you may wish to purchase a service manual from a dealer or take advantage of an online service such as where you can converse with a small engine mechanic and they can walk you through the process for a small fee.

Good luck!


My Lawnmower is ........

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