How often do you change your spark plugs. I have a Mercury 150 horsepower and did not change them this year.

I run a Mercury 150 and for piece of mind I change them out every six months. Keep the old ones handy just in case i foul one, although I have yet to do that.

I've not changed mine in 2 years but I do check them monthly & keep a new set onboard.

Every 100 hours which translates to about once every 2 years.

I change mine twice a year in my 1967 Evinrude 80.

Sorry to hijack the thread but, what damage could be cuased by not changing them regularly?

Sorry to hijack the thread but, what damage could be cuased by not changing them regularly?

Poor performance, hard starts, and possibly fouling one from extended idling time.

I inspect all of them once a year and single plugs from time to time and like Catt I keep a spare set in the boat. Years ago I changed and inspected the plugs more frequently but with my 159 I run it pretty hard or not at all and it is far less prone to fouling.

I keep a spare set in the boat that I have already index'd and numbered for which cylinder they go in.  I change my plugs when they start causing a problems or until I've run them to the point that I think it's time.  I've been running the same set of plugs in my DFI motor for about three years, and for no more than I'm fishing now, I may run them another three years.   On my two hot rod motors, 50 - 75 hours is about all I can usually get out of a set.

I have a VP 135 hp engine in my Glastron GS 185 Ski & Fish.  I store it for five months of the year.  I change the plugs after I run the tank full of stored gas (treated w/ Stabil) out of it in the spring.  I figure $25 for plugs is a good investment for a six month period of boating and fishing enjoyment.

Change mine based time interval manufacturer recommends.   

150 Mercury Should use NGK BU8H and you can get them for about 1.65$ each for that price I would change them every month if you fish alot mine cost 4.85$ and i change them ever month weather they need it or not But thats just me