How often is this genset run?  If it's not too often I bet the
generator slip rings are oxidized and the v-reg can't bost the voltage
up enough to produce the needed current.

Mickey

It sounds like it is shutting off? It really sounds like it needs a tune
up- new plugs and points (if used),new fuel filter, run a good fuel system
cleaner through the carb, maybe a treatment with Onan "4C" de-carbon
treatment, and cleaning the spark arrestor on the muffler (remove the
small brass plug on the muffler and run it under load for a bit).

Sounds like the generator brushes are worn and want to be replaced..

kelly

There's two parts to this. The engine has to be able to put out the power
demanded by the generator end, and the generator end has to be able to put
out the power needed for the load you're trying to run.

   If the engine runs rough and the speed drops noticeably as you try to
add more load, then it's probably an engine problem.

   If the engine is running smoothly as you add load, but then just
suddenly cuts off and dies, then it's probably a generator problem.

   In my experience with 6.5s in typical use, the FIRST thing to do is to
make sure it's actually running on both cylinders. Feel both sparkplugs
after running for a minute or two - if one is warm/hot and the other is
cold, you've identified your problem. If that WAS the problem, you need to
clean or replace the offending sparkplug to get it running on both
cylinders - and if it's been this way for very long, you should also change
the oil, as it'll be diluted with gasoline that has washed into the
crankcase from the non-firing cylinder.

   If it's running on both cylinders, but the engine won't handle a load,
first check that the altitude adjustment (main jet) on the bottom of the
carb is set correctly. If it is, then your best bet is a tuneup done by
someone with the equipment to make adjustments under load. It SOUNDS like it
could be a fuel supply problem - but there's a long list of things that
could be involved.

   If it's running smoothly, but just cuts off entirely when load is added
without the engine slowing, stumbling, etc, then you may have a generator
problem. Most commonly, tarnish buildup on the slip rings limits the
generator output, and adding too much load will drop voltages enough to
cause the genset to drop out of 'run' mode.

   More information on what it's doing would be helpful in deciding which
branch of the troubleshooting tree to follow.

Alan

When my generac quit working right under load, I hauled it in and had
it looked at.  Turned out to be something stupid: air filter.  Check
yours first, it'll save you a ton of money and looking foolish if that
is the problem.