I've heard horror stories of mud daubers building nests in boat motors causing damage. I've not had this trouble but I keep my boat in a tin shed that has lots of nests. How do I prevent them from building a nest in my motor? How can I check for nests, is there a common place on the motor they build them?

I don't know how to prevent them, but when I help out my boat mechanic I've seen an engine that had over 150 nests under the cowling and inside the lower unit...It was amazing and disturbing...

Use Moth balls inside the cowling. Put them in a stocking and when ever you're ready to use the boat. Pull them out and leave them at home. By the time you get to the lake..no smell... P.S.also works great to keep rats out from under the tarp and other varments...just place a pie pan full of balls and the critters get the message real quick.

The most promenent place for wasp to build their nest is around electrical wiring, under the flywheel and they love the air box in front of the carbs.........

What Mike said +1

i never thought about wasps in the cowling until I opened mine about a year ago and found the all along the inside of the cowling.

Thanks Mike, I'll give the moth balls a try.

I've seen mud daubers build nests inside the water discharge holes on V4 OMC engines. We stopped it by carving two corks and plugging the holes loosely. I say loosely, because they will blow out once you hit the throttle, in case you happen to forget to remove them.