^^ what he said. Its like 1/2 a quart or so.
One US quart is .987 L or 987 mL.
So 650 mL is 2/3 of a quart (or 21 fl oz, 1.5 pints, or 38 cubic inches of liquid depending on how you measure it).
I have the same problem. I just changed the oil and cleaned the outside of the glass, but can't see shi..... Looks like I am taking off the cover and cleaning the inside. Better safe than S.O.L.....
Just an FYI, the area between the center cases is not "flow-through" to the clutch cover easily. It takes a long time for it to "seep" through the sealed bearings. However, if anyone had ever cared to take notice.... the clutch cover and center cases share a distinctive feature. At the very back of both, there is a "catch basin" and a "pass-through". Of course, 650mL of oil doesn't reach that high BUT when the engine is running the outer ring gear on the clutch IS dipping into the oil in the clutch cover and throwing it all over everywhere. This catch basin and pass through is designed to catch what the clutch basket is throwing around and run it into the center case halves to lube the transmission. If you filled up the clutch cover, waited about 1/3 of a second, didn't start the quad, and tried to look through the sight glass you will fail horribly.... the level in the clutch cover will be FAR above the sight glass.
The trick to the blaster sight glass is as follows. Drain out the transmission fluid completely (make sure the blaster is flat and level because there are pockets in there it can hide if the quad isn't level) and reinstall the drain plug. Take off the filler plug and pour in (preferrably using a funnel so you can be halfway accurate) 2/3 of a quart of wet clutch compatible liquid. Re-install the fill plug and start the quad. Drive it around the yard real quick to make sure you filled the transmission area up to the "proper" level and come back to check the fluid level through the sight glass. The idea behind the sight glass isn't to make sure you put the correct amount of oil in during a change but to be able to check the current level in the transmission during a ride (to ensure you aren't going to run out)
I *believe* the manual specifies checking the level with the engine off but I actually like to do it with the engine idling. It usually requires I add just a BIT more fluid but I'm ok with that, just a tiny bit extra insurance for my transmission if anything happened.... If you have to add any more than a little dribble to it, you're adding too much. OVERFILLING THE TRANSMISSION FLUID CONSIDERABLY CAN CAUSE PERMANENT DAMAGE TO THE RIGHT SIDE CRANK SEAL. Never put more than 3/4 of a quart of transmission fluid in your bottom end or the hydrostatic pressure on the outside of the seal can "push" the seal inwards and actually cause your engine to start burning your transmission fluid.
If your engine is already burning transmission fluid (fluid's disappearing, no leaks, no drips, and your blaster's exhaust smells like ass are good indications) you waited WAY too long to find the source by doing a leak-down test and determining you had an air leak. You need to stop running it immediately and pull the right side (clutch side) crank seal out and replace it after doing a leakdown test to confirm that seal is leaking (and not the case halves behind the balancer gear or the transmission).