Newb needs help - Leaky cylinders? Bad plugs?

[jm999]

I put these plugs in less than two weeks ago and have fired the engine up on muffs, and a few times out on the lake last weekend. The motor ran like crap on the water, wouldn't go into gear without stalling, wouldn't idle for long, etc... Ran fine on muffs though.

I'm taking the carbs off for cleaning today and I noticed that all of the cylinders seemed to be leaking gas/oil. I removed a spark plug and noticed it looked pretty nasty for being brand new, but I'm not an expert. Also noticed gas/oil pooling up around where the spark plug screws in.

Just wondering if this is normal, or a symptom of something wrong.

 

[Redneckhick]

Re: Newb needs help - Leaky cylinders? Bad plugs?

Are you sure that is the right spark plugs for that motor? Looks like a automotive plug to me.

 

[jm999]

Re: Newb needs help - Leaky cylinders? Bad plugs?

I bought it from Lowes. It was exactly the same size/thread as the ones I pulled out of there. Guess I'm showing off my newbness here. Probably using the wrong plugs then? My manual says to use J4J, but I couldn't find them anywhere. These ones are J8C and was the closest that I could find to the ones I pulled.

Motor is a 1964 Merc 850

 

[Jake_MN]

Re: Newb needs help - Leaky cylinders? Bad plugs?

That's a lawnmower plug. J4 and J6 are marine plugs. I'd get correct plugs before worrying about leaking cylinders.

http://www.vintageoutboard.com/Sparkplugs/SparkPlugs_1.html

http://store.usavediscountmarine.com/Champion_J4C_Spark_Plug_p/chp-j4c.htm

http://www.nextag.com/Champion-Marine-Spark-Plugs-766576881/prices-html

 

[Chris1956]

Re: Newb needs help - Leaky cylinders? Bad plugs?

J8C is the correct replacement for a J8J plug. You should be running a J4C if the motor originally called for a J4J, which I do not know to be true or untrue. J4J was used in most of the Johnnyrude motors int th e50s,60s and likely the 70s.

I would doublecheck the spec. for the spark plug. I would also inspect the carb floats, inlet needle seats and float height. A service manual would be a real help to you.

 

[jm999]

Re: Newb needs help - Leaky cylinders? Bad plugs?

Thanks for all of the info folks. Guess I should have known.

I have a PDF version of the original manual for this motor that says it uses J4J plugs. However my Clymer repair manual doesn't specifically cover my year, but says Merc 650, 800, and 850 with Thunderbolt Ignition takes AC-V40FFM or L77V?? I'm not sure if my 64 Merc 850 has a Thunderbolt Ignition.

 

[Jake_MN]

Re: Newb needs help - Leaky cylinders? Bad plugs?

I stand corrected. I never knew there was a J8 marine plug. Apologies.

 

[jm999]

Re: Newb needs help - Leaky cylinders? Bad plugs?

Just called Advanced Auto and they said they have the J4C equivalent in an AC Delco. Would this plug work, or do I have to buy marine-specific plugs?

Thanks again.

 

[merc850]

Re: Newb needs help - Leaky cylinders? Bad plugs?

The Mercury manual calls for J4C gapped at .025" and the dwell on the points - (no Thunderbolt until 1967) 90*. Have you checked the points in the distributor?
The higher the Nr. the hotter the plug burns which may cause pre-ignition when running at full throttle.
You have to set the low speed adjustments with the engine running in gear 800-1000 rpm.