1965 3.9hp plug fouls

[Teseal]

#1885875

 

[Teseal]

Something I had seen researching made me think it was a '65 but I can't find it now

 

[racerone]

Any pictures of your motor.------Cowling and with cowling off ?----Somehow I think that the parts listing is wrong for a 1965 model 3.9 HP

 

[Teseal]

Sorry racerone I missed one of your posted questions, I did not look into the ignition because I could get the spark to jump 1/4" as mentioned in my first post.

 

[Teseal]

Let me try to get some pics for you.

 

[Teseal]

Here's some before and during some of the service that I just happen to have on my phone. Needed to remove the power head to replace the shift linkage shaft. If you would like something more please let me know

 

[Teseal]

It's a 1966 model 3.9 (39)

 

[racerone]

The cowling clearly appears to be a 1965 to me!----The ignition system on your motor is totally different from what is in the listing per post #19

 

[Faztbullet]

Spark plug should be a B5HS.

And this shou;ld be correct ignition system as the one posted is for a 4hp(40).

 

[racerone]

+++ on the above.----That looks more correct for a 1965 model !

 

[Teseal]

All I can tell you is the Mercury SN chart lists it as a 1966. https://www.marineengine.com/mfr/mercury_models.html
Either way when I get a chance I'm putting one of the J plugs although not sure which because of all the conflicting info

 

[racerone]

The decals / cowling is clearly a 1965 model to me!----Some will argue---But I would pull the flywheel.----Replace condenser.-----Clean and set breaker points.----Great little motor and should run like a top all day long.----You have installed a new water pump impeller I hope.

 

[Teseal]

Yeah new pump and prop shaft seal. Guess I should check the ignition even tho it seems to be doing it s thing.

The B5HS plug came up in a previous comparison I did.

The parts list pic post looks the same as the one posted by iBoats but it lists the L78v plug as only available. So I have 3 suggestions for the correct plug, J8C or B5hs or the J6c I crossed to, all J style. I'm betting either will get this little motor doing its thing.

 

[racerone]

The 1965 model never had a module / stator assembly under the flywheel.----The L78V was never specified for the 1965 model 3.9 Mercury.---Never !

 

[Teseal]

OK so doesn't that also support it being a '66 rather than '65 ???

 

[merc850]

According to the Merc manual the 1964-66 3.9's used a J7C plug and the gap is .025"/ the points should be set at .020". Your motor falls into those years.

 

[racerone]

I know what the cowling of 1965 model Mercury looks like.-----Good luck with your motor.

 

[Teseal]

OK thx much

 

[Teseal]

merc850 appreciate the info. For some reason I didn't see your post and got a J8c plug. That keeps it running now but there is still a carb issue I'll need to look into.

 

[merc850]

The Nr. refers to heat range - The middle number indicates the heat range of the spark plug, the higher the number the hotter the heat range the hotter the plug the less it will foul.