I have a Guardian RV 3600 watt generator than wont run more than a few seconds. I have to hold my hand over the breather to get it to fire then as soon as it revs up it shuts off.

regulator maybe need to adjust or broken

If it backfires, check for manifold leaks, fuel mixture is too lean, timing is off, make sure it isn't spitting liquid into the cylinders and the LP is the right pressure, and the vapour coil is working

It may be demagnetised. If you turn off the generator before unplugging the load this may happened. Try to put a strong magnet (like those from loudspeakers) in contact with the body of alternator. I do this in the past and it work.If you do not know how to do this ask an electrician, he can help you .

Check for low oil or over temp.

Johnny,

If generators are not used regularly, they need the their magnetic field to be charged (or flashed). This can be done by plugging an electric motor into the socket while the generator is running and spin the motor by hand. The hand-spun motor will push some electric current back into the generator and magnetize it enough to start it.

Look in the manual. There is likely something about field flashing the magnetic field. The easiest way to do this is to.
1) start the generator
2) plug an electric drill into the generator (without drill bit)
3) make sure drill is set to forward direction (if a reversable drill.
4) pull the trigger on the drill.
5) If the drill does not start, spin the drill's chuck clockwise (When looking down at the chuck from the drill bit end). Spin counter-clockwise if holding it like a pistol and pointing away from yourself.
6) Do this several times (hard) until the the generator will kick in and suddenly make the drill spin at full speed.
Be careful not to drop the drill or poke someone with it as you celebrate success.

When they sit allot - sometimes the fan will stick.. Take the cover off,, turn it on and see if the fan is stuck.. Spin it by hand to free it up..

Your control board is faulty. Try to power up the ingnition coil as well as your fuel pump. If this does not get the engine running then you have major engine problems.

Before starting the genset remove the air filter and check the throttle plate on the carberator, it should be closed. If it is opened, then you choke coil is worn out and needs to be replaced.

This story ends with bad gas and silicone in the gen tank

Is this an RV generator?

If you have to really choke an LP engine but it runs more or less normally once started you need to troubleshoot the demand regulator and the fuel supply lines (look for air leaks). I'd also check the fuel inlet pressure before the demand regulator.

Rate me,
Carl