I put an extra 3/4 qt oil in the engine - the level is at the top of the L-->H on the dip stick - what am I risking by not draining the extra????

 

Air mixing with the oil and causing it to foam. This causes drop in oil pressure and lack of lubrication in critical engine parts. The result could be the same as not having any oil. Go to a boat supply store and get an oil pumping kit you can attach to a drill motor and pump some of the oil out from the dipstick tube.

 

3/4 should be too bad. you will be fine i think

 

Too much oil also can cause your pistons to sit in oil bottom dead center. Causing.... the pistons to be impeded. Imagine your hand hitting water.... like that. Losing HP and TQ. Loss of momentum.

 

You're at the H mark, you're fine.

 

It's not an excessive amount, especially since you're on the H side. For future reference tho, too much oil can sometimes result in high pressure in the crankcase, you can get oil leakage through the oil pan gasket and other engine seals. You might notice some reduced gas mileage if the level too high - it's possible that the crankshaft will splash in the oil, which makes it work harder and will cause it foam a bit. This could in turn cause the oil pressure in the crankcase to drop and perhaps lead to premature engine wear or even damage. But, like I said, 3/4 of a quart isn't excessive. If you're concerned and don't mind getting dirty, drain a little bit out thru the drain plug (only when it's cold though). Good luck and I hope this helps.