OT - generator problem

 Spodes -

I just bought a 5000W generator yesterday - 10HP Subaru motor.  I
fired it up for the first time a few minutes ago, and it doesn't run
correctly.  Instead of running smooth and constant, the RPMs oscillate
up and down.  I put a light load on the generator (small air
compressor) and there was no effect.  I would guess that the problem
is caused by an underdamped control circuit, but the behaviour seemed
to get worse after I turned off the gas to let the carb run dry, so
maybe it is a carburation problem (float set too low?).  I'd simply
return it, but I don't think the store has any left - and I'm a sucker
for a challenge.

Any advice on how to debug this issue?

Thanks - JayC

 
Have you searched on its specific model number for problems?

Do you have any way of measuring the engine speed, or the frequency of
the output?

On these usually the output freq is managed via engine speed, so if
you can measure the frequency you can tell if its running too slow and
surging towards the proper speed, or too fast and dropping down to the
right speed, or oscillating around the proper speed. Don't know if
that'll help *fix it* but at least you'll know which way to adjust it
once you find the magic screw.

Maybe it sat in stock for awhile and it has a nest somewhere blocking
the airflow to the feedback vane/paddle?
Or does it have an electronic speed control?


Dave

 
JayC wrote in message

This is common on small gasoline engines with cheap governors or perhaps
cheap carburetors.  It is called hunting by the local lawn mower shop.  On
the snow blower there is a screw in the center of the float bowl, on the
riding lawn mower there is a screw with a plastic attachment so you don't
over adjust it.  running with the choke partially closed seems to cure the
problem for the most part before warmed up and adjusted sort of right for
when warmed up.

Fran

 
Correct and correct.  'Hunting' behaviour is consistant at a few
hundred RPMs, but occasionally amplitude increases to where RPMs drop
by half or so.  Partial (2/3) choke cures hunting, so it appears to be
a lean condition, although it didn't need to be choked to start.
'Hunting' behaviour doesn't seem to change much as the motor warms
up.  I pulled the carb apart and it was spotless - weird sideways main
jet configuration, it uses a small round jet.  I shot carb cleaner
thorough everything and put it back together - there was no change.

I don't know if it's just the dirtbiker in me, but I'm wondering if
the machine is jetted for moderate temperatures and it's just too cold
to run properly.  It WAS somewhere in the 10-15 degree range outside
when I was running the motor.  Maybe I just need to re-jet for winter?

JayC

 
Just found this on an AR15 forum - someone else in NH was having some
intermittant hunting issues with his generator during the big ice-
storm/blackout.  Someone suggested lean operation:

"The other thing you need to realize is that new ones run quite lean
thanks to the dorks at the EPA, they are leaned out almost to the
point of not running correctly and most if not all have a main jet
that is not adjustable. Even the tiniest bit of gunk, low octane fuel,
old gasoline, water etc will cause a stumble at load in the best of
conditions. I cheat and usually open mine a bit with a oriface drill
[from .30 to maybe .31 or .32 or so] which usually fixes 99.9% of the
lean running conditions."

If my generator is overly leaned out due to EPA restrictions (and I
think it's even a California-compliant model), then not being able to
run at 10 degrees F ambient I guess doesn't really surprise me.  I
don't think a stock-jetted XR would run at 10 degrees either.  Could
it be that simple?  My generator even has a removable main.  Gawd
knows where to look for appropriate jets though.  And where do you
find 'oriface drills'?  The jet hole is about as big as a human hair -
can't say I've ever seen drill bits that small, much less whatever
kind of tool you need to put them in.

JayC