1965 Merc 900 spark plug

[vampirefish]

Hello all. I'm going to replace the spark plugs for my 1965 Merc 900 (90 hp) outboard (inline 6) and have ran into a couple issues. <br />1) Type of plug in the engine now: What's in the engine now are NGK BUHX (surface gap) plugs. My step-dad used this type for years. I went to NAPA to replace them and they only had NGK BUHXW-1. They said that these run hotter. Do you think I can use these? <br />2) What type do I need?: It's hard to tell what my manual recommends for many things regarding this engine, because although I know that I have a Merc 900 it's rarely mentioned in the manual - seems to be quite rare. So for instance, my wiring diagram is not listed but matches the Merc 1100 and 950. There are only a couple tables that I can find that actually have the 900 listed. When I look at the spark plug table (in my manual) it is listed but recommends a Champion J4J with a 0.025 in. gap. Wouldn't that be NA if I use what's in there now? Maybe I have the wrong plugs now? <br /><br />Any suggestions would be mucho appreciated.<br /><br />THANKS!

 

[Laddies]

Re: 1965 Merc 900 spark plug

The I/6 were designed to run on J4J=J4C. A hotter plug can damage the engine

 

[vampirefish]

Re: 1965 Merc 900 spark plug

Wow - sounds like it was running on the wrong spark plugs! Would this be BAD for my engine...? My step-dad never had a manual for this so probably just used the same ones that were in it when he bought it. What's the difference between a J4J and a J6J (just curious)? THANKS SO MUCH!

 

[Laddies]

Re: 1965 Merc 900 spark plug

J6C is one range hotter a lot of people that run at slow speeds ran the hotter plugs to help fouling back then, No problem inless ran WOT for a distance

 

[vampirefish]

Re: 1965 Merc 900 spark plug

Laddies regarding what you replied:<br />J6C is one range hotter a lot of people that run at slow speeds ran the hotter plugs to help fouling back then, No problem inless ran WOT for a distance <br /><br />How long of a distance are we talking about at WOT? I plan on taking my kid out tubing, skiing, fishing. Probably more sports-related stuff than anything. I bought the J6J's yesterday and finally got my engine running (thanks to this forum)! SWEET ! But...not sure if I should stick with these or use the J4J's.

 

[Clams Canino]

Re: 1965 Merc 900 spark plug

Tubing and skiing is not done at WOT - only the hole shot is...<br /><br />Also - you have a 2-coil ignition or a CDI? 65 was former - 66 later.<br /><br /><br />-W

 

[vampirefish]

Re: 1965 Merc 900 spark plug

I have a 2 coil ignition.

 

[Clams Canino]

Re: 1965 Merc 900 spark plug

Then listen to Laddie and get the right plugs - don;t tkae any chances. <br /><br />-W

 

[vampirefish]

Re: 1965 Merc 900 spark plug

Thanks so much! I have the J6J's now so will stick with those. <br /><br />I LOVE THIS FORUM!