What kind of life should I expect from the plugs in a 75 hp optimax? It uses NGK IZFR5J plugs,I found a autolite plug that is supposed to cross over(it was 1/4 inch too short)it didn't work the motor still had a miss at low speed.the motor hasn't been used enough to be having problems.The plugs I found on line were $10 to $12 each and I can't find any locally.I really hate to go to the marine dealer and pay him $100 to put it on the computer but I don't know what else to do.

If i was on the stick (which im not) i would change plugs once a year as i put on 200- 300 hours per season The correct spark plug is very important Take your NGK plug to the parts store and either replace it with NGK or have them cross it over to another brand with the same heat range This should save you some money vs buying them from a marine store. If you still have a miss you need to get it to the shop right away because if it is a plugged carb you will have a cylinder or cylinders that are not getting proper lubrication due to the lean condition The end result will be catastrophic engine failure and it don't take very long for it to happen!!!!

I run an Opti and get my plugs through O'reilly auto parts. They cost me about $9 and I change them every 100 hours whether they appear to need changing or not.

+1

The low emission motors really chew through the spark plugs. They tune the motor to run the the combustion chamber so lean, which results in very high temps, that it melts the igniter off the plug rapidly. It's recommended to replace them every 75 - 100 hours of use.

try spark plugs.com i would only use the ngk plugs tho. also use merc oil will help.

Stay with the NGK's as that's what Mercury specs. I get mine at NAPA (know how) for half the price that the marine places are asking.

are those platinum plugs? the mechanic at Cabelas told me all you really needed to do with them is clean, gap them and put back in. They were about $20 a plug too. I have 2001 Opti also