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James W
James W, Small Engine Troubleshooting Expert
Category: Small Engine
Satisfied Customers: 3708
Experience:  7 years as Mechanic & Parts Manager for Brother who has Owned Lawn & Garden Repair shop for 35 years
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I deliberately ran my Craftsman Generator 4200 watt, 7.8 HP

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I deliberately ran my Craftsman Generator 4200 watt, 7.8 HP out of gas because I was afraid the gas would get old. I didn't crank it for a year.

Now when I try to crank it, it fires right up, runs very rough for a few minutes and then shuts off. It acts like it runs the gas out of the carburator and stops. You have to keep it half choked to make it run for the few minutes it does run.

The generator only has about 30 hours on it. I have sprayed Sea Foam lubricant on it and in the tank. The fuel line out of the tank going into the carburator lets the fuel into the carburator but I don't think it lets enough go in. I tried to blow air up the line going into the tank. Didn't help

Unfortunatly, a few drops of fuel are still left in the carburetor when you run it out..

This has dirtied your carb..


As they sit, fuel that is left in the carburetor can turn to gum and varnish and cause this and other problems.

Also, any gasoline that was left in a gas can for a period of more than 30 days must be discarded because it also has begun to turn to varnish.

More than 70% of all of our repairs in our lawn mower business are due to this same issue. You most likely have dirt, gum, varnish...etc in your carburetor plugging up the small passageways and jets in the carb. It Must be removed from the engine, cleaned very well, blown out with compressed air and reassembled using a NEW carburetor rebuild kit. ALWAYS clean the fuel tank and replace the fuel line when doing this repair or you may have to do it all over again. The inside of the fuel line disintegrates over time and these small pieces of rubber will plug up the carb too. Dirt and water from a dirty fuel tank will also plug up the carb. Find the Model, type and serial or code numbers off of the engine and take them to your local dealer to get the carb kit.


First make sure that you have the correct complete carburetor repair kit.


Now take special care when you take the carburetor make sure that you watch and remember exactly how the gaskets come off.


Remove the float pin just pushes out...and remove the float..carefully.. so you can see how the float needle is attached...(Some of them have a small wire spring holding it to the will have to reinstall this spring when you reassemble the carburetor.


Next...remove the float valve seat. most of these have a screwdriver slot to allow removal. Look around the carburetor and see if it has a small idle adjustment needle...remove this needle if it has one. You are now done disassembling the carb. DO not take anything else out of the carb.


Get a good carburetor cleaner....preferably with a small hose you can attach to the nozzle of the can. Spray the carb cleaner all over the outside of the carburetor. this will loosen the dirt on the outside while you clean the inside. Now spray the cleaner through every hole, and nook and cranny you can fine on the inside of the carb.


When you are finished with the spray,blow all of the passageway clean with compressed air from an air compressor. Also blow all of the dirt from the outside of the carburetor.


Next. Take the entire carburetor to the kitchen sink......Ok maybe it would be better to get a big you don't make your wife mad....and wash the entire carburetor with HOT SOAPY dishwater. This is to make sure that all of the carburetor cleaner is completely washed from the carb...(If it is not, you will deform the new gaskets and such that you install...even if it is dry.) Now rinse in clear watter and then blow the carb dry with the compressed air again.


Reassemble the carb using the identical parts out of the carb kit as you took out. install the float seat, then install the float needle and the float in the same position that you took them out. Check the float level after it is installed. Making sure that when the carb is upside down with the float in the up position, the float should be nearly level with the body of the carburetor. Now reinstall the bowl gaskets the same as you took them off. Then install the bowl nut with the small gasket under it. Reinstall the small idle needle if it had one.


There you are done.


Install the carburetor on the engine and you should be ready to go.


Is the unit producing electricty when it is running??

Often, generators that sit need to be flashed before they will produce any electricity.

If not try this:


Field Flashing of Portable Generators

This tip comes from the Briggs & Stratton Customer Education Department. As an alternative to flashing a rotor winding with a battery applied to the brushes, an electric drill may be used. Follow these steps to flash the generator:

  • Plug the electric drill into the generator receptacle. (Cordless drills do not work)
  • If the drill is reversible, move the direction switch to the forward position.
  • Start the generator
  • While depressing the trigger on the drill, spin the drill chuck in reverse direction. This will excite the field and the generator will now produce electricity. If spinning the chuck one direction does not work, try spinning the chuck in the other direction as you may have the reverse switch positioned backwards.


Use caution not to get your hand or other materials caught in the chuck. As soon as the field is excited, the generator will produce power and the drill will turn on.

The reason this works is because the electric motor in the drill will act as a small generator when spun backwards. The magnets in the drill's motor induce a voltage into the motor windings, which is fed back through the trigger, cord and into the generators receptacle. From there it goes into the power winding of the stator. The voltage going through the power winding creates a magnetic field, which is intensified due to the iron core of the stator laminations. The rotor intersects this magnetic field as it is spun past the power winding, thus inducing a voltage in the rotor winding. Once current flow is present in the rotor winding the rotor has been flashed.

If flashing the field does not make the generator work, you may have additional problems, besides a lack of magnetism in the rotor. Further testing will be needed. Hopefully, this will give a simple way to field flash your generator if needed



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