When any engine starts, runs momentarily, and then dies usually indicates what is called “fuel starvation.” There could be one or more of several possible causes.

Without personally doing a “hands on troubleshooting” of your machine no one here can be sure of the specific cause. The running after putting some gas directly into the carb throat indicates that the ignition, timing, and valves work properly, and that the problem is getting the fuel from the tank through the carb. For some reason, fuel is not gettng through the carb to the intake manifold and engine.

First, go to your local auto parts store [Autozone, Advance, O'Reilly, Carquest, etc.] and get a small bottle of Fuel System Cleaner, or Fuel Injector Cleaner, or a similar cleaner. Add about 2 tablespoons of the cleaner to FRESH, CLEAN fuel in the tank.

You don’t describe the type of fuel system you have so it’s difficult to advise. However, here are some possible causes:

1. If so equipped, the fuel cut-off valve at the tank or in the fuel line is turned OFF.
2. The tank fuel outlet, fuel line, or in-line fuel filter [if so equipped], are clogged/blocked.
3. Sometimes there is a small filter inside the fuel tank at the fuel outlet, and it could be clogged.
4. If the carb has a float valve, it could be stuck in the closed position.
5. On 2-cycle engines with a “Primer Bulb,” if the bulb, or the “Return” fuel line to the tank are cracked or split, then air can enter, which can interrupt fuel flow.
6. If some tiny grit, or gum, or varnish [from old, stale, evaporation thickened fuel] collects in the idle and/or main carb “jets,” that can cut off fuel flow from the carb to it’s intake venturi.

This situation can sometimes be corrected by backing out the jet adjusting screw a couple of turns [be sure to precisely count the turns so you can put it back EXACTLY like is was before, after you get the engine running]. With the jet adjustment screw backed out, add some fuel directly to the carb intake opening. Then start the engine, and let it run until it quits. Repeat this several times. After a while, when the engine begins running on its own, then reset the jet adjusting screw like it/they was/were before.

7. Inside the carb, there are several very small, actually tiny, passages called “Galleries” which can become blocked by old, stale fuel due to evaporation. This gummy material is composed of material called gum or varnish.

IF this is the cause of the problem, then the only fix may be to dissemble the carb, remove all non-metallic parts, and then SOAK the carb and all metallic parts in a liquid carb cleaner [like Berryman B-12 Chemtool also available at your auto parts store. Be VERY CAREFUL to FOLLOW the label DIRECTIONS [PRECISELY] as this chemical is very strong and can burn your skin, and cause blindness.

After soaking the carb in the cleaner, per label directions wash the cleaner off and allow the carb to fully air dry. Then reassemble and install the carb. Although not absolutely necessary, I strongly recommend, that since you have the carb torn down, installing new parts from a carb “Rebuild Kit,” also available from your auto parts store.

These gum and varnish problems are usually caused by leaving fuel in the tank and carb system for extended periods of time over the “off season.” To PREVENT this, pour or siphon all fuel out of the tank and then run the engine until it quits. This gets almost all of the fuel out of the system, and if there is no fuel to evaporate, then there will be no gum and varnish, and with fresh fuel the engine will start with no problems. Good luck. bushmaster8