In theory - and in MOST installations - it should be possible to adjust or
change the points/condenser and/or check voltages at the coil without
dropping the genset. How easy it will be depends on the installation -
please don't blame Onan for something done by the RV manufacturer or dealer
who installed the genset.
   If you go to
http://www.smallenginewarehouse.com/product.asp?PN=Onan-RV-Engine the two
pictures on the right of the page should be VERY similar to the engine
portion of your genset. On the bottom picture, the circular part closest to
you (silver on the inside) is the adapter from the engine to the genset
housing. Just above it, you'll see the stamped metal cover over the points
and condenser that I mentioned. On the right you'll see the coil, on the
left the carburetor and air cleaner assembly.
   Since you're used to doing tuneups on regular cars, the only things that
might be confusing on how the -engine- works would be (1) the ignition. It
doesn't have a distributor - instead, the coil has two high voltage
terminals, and sends spark to both cylinders at the same time. Since it's a
horizontally opposed engine, that means that one cylinder is firing just
before top dead center on the compression stroke and the other cylinder is
sparking just before top dead center on the exhaust stroke - no mixture to
fire, but doesn't hurt anything. The next revolution, the cylinder that was
on the compression stroke is now on the exhaust stroke, and the cylinder
that was on the exhaust stroke is now on the compression stroke. Again, one
spark is wasted, but doesn't hurt anything. The points under the cover are
actuated by a pushrod which runs down into the engine and rests on a lobe on
the camshaft.
(2) the throttle. To produce 60HZ, the engine has to run at 1800 rpm - so
the throttle is opened and closed by a governor to maintain as close as
possible to the desired speed. You can see the external parts in the
pictures above - a linkage arm with an adjustable spring that's holding the
throttle wide open. The part you can't see inside the engine is a
centrifugal mechanism that exerts more pressure to close the throttle the
faster the engine is running - so the speed the engine runs is a balance
between the spring tension pulling the throttle open and the centrifugal
pushing the throttle closed - you increase or decrease speed by changing the
spring tension. If the load on the genset changes, the governor will open or
close the throttle as needed to try to maintain 1800 rpm. This leads to two
important things - when the genset is running the governor should be the
only thing setting the speed - the idle stop screw should NOT touch - and
the only way to get the genset to wide open throttle so you can properly set
the main jet is with a load bank.
   Hope this is enough to get you by until the manual gets there. If not,
go to the dealer locater at www.funroads.com and look for a dealer near you.
I'd be willing to bet that the rv center that changed the board isn't
listed..

Alan