Re: 225hp yamaha excel 1988, timing is -5 degrees at idle after manuals instuctions
revving a two stroke with no load,not to be blunt, is plain stupid and shows absolutly nothing.
that system uses a crank position sensor to signal RPM and a throttle position sensor to signal throttle opening.
with no load it may only take 30* of throttle angle to make 3800 and the ign timing is going to only give enough for the commanded throttle angle and RPM.
most likly with no load and 4 spark plugs tossed in the creek you could still hit about 3800 running on two plugs.
so quit the revving with no load, its not only meaningless but can lead to bearing damage.
one of the easiest ways to control engine RPM at low speeds with carbs is to alter ign timing,farther you retard it slower it goes.
as on a crbed motor its difficult to alter air or fuel into the intake the simplest way is to retard engine timing electronically.
4 strokes only make a power impulse every OTHER time the piston is at TDC and they also have to drag a valve train with them.
two strokes make power EVERY time the piston comes up.
most 4 strokes you will see idle something close to TDC, most 2 strokes are around 7 ATDC.
best thing I can tell you is carefully follow the YAMAHA service manual and learn what and why each sensor is on that motor and what the A-B connectors do and when would you ever need to touch them.
that was an early venture,crude as it was, into electronicly controlling a carburated engines ign charecteristics to make it more efficient.