This may be an odd question for some but how long can you leave your motor running on muffs?  I can't imagine leaving the motor running for an extended period of time would be good for it but then again it is getting water so overheating shouldn't be an issue is it?

My 225 Opti was giving me a low oil last year. I took it to a local shop and they had it on muffs for over an hour trying to figure out the problem. It wouldn't over heat and kept oiling but the buzzer kept going off. It turned out to be the float in the upper oil tank. But it still cost me $100 for the muff time.

Some guys will tell ya not to leave them runnin with muffs any longer than is absolutely needed. If I have to muff it, I usually don't let it run longer than 10 minutes or so. However, me thinks you can leave them on a lot longer than that with no ill effects, as long as your hose has good pressure and the engine's not building up any excessive heat.

I'm sure there are some engine guys on here that could tell you exactly what the dangers would be.

I've got a Mariner 150 Mag that I've had for 24 years, used muffs hundreds of times. It's still got good compression. Truthly, most of the times I run it in the driveway, I do it to  annoy my one and only neighbor. Those older 150's are  loud when out of the water, and if the barometric conditions are right, I can create about a half an acre of the prettiest blue gray clouds you've ever seen and the prevailing breeze always seem to take them next door.

As long as you have ample water going through it, there is no time limit.  It's just the longer you run it, the more carbon is going to build on the pistons and plugs, so there's the chance some plugs will foul the next time you go to start off at the lake.

Just never rev it over 2,000 rpm with it on muffs or in neutral.   There's nothing in the world that will make you mess up a pair of drawers any quicker than having you're two stroke outboard in runaway.