Changing Out Carburetor Jets

[Walt]

My Merc 50hp ELPTO 2cycle has carburetor jets for high altitude since I live in Denver. I want to take the boat to Missouri and Tennessee this summer for a couple weeks and the dealer said the jets have to be changed for lower altitude. Does going from higher to lower altitude change the preformance so much I have to change the jets? Anyone have problems with their motors who did not change them out? Thanks for your help!

[Starfish]

Going from higher altitude to lower altitude makes engines run leaner (there's more oxygen molecules in a given volume of air). So you can overheat and damage a motor if you don't re-jet. Conversely, running at higher elevations can cost you power because you're running too rich, but it generally won't damage anything (other than some plug fouling) because running rich won't cause overheating.