spark plug query

[nwcove]

any difference between a champion uj4j and a ql77jc4 ? ( 1974 evinrude 25 application)

 

[kbait]

Re: spark plug query

Well, a '74 evinrude 25hp would have points ignition. QL77JC4's are for CD (electronic) ignition motors. Your motor calls for Champion J4C's.. unless it's been converted to CD ignition. Never heard of a uj4j.

Good luck!

 

[boobie]

Re: spark plug query

I just went to my OMC P&A book and there are no uj4j plugs listed any where. Check with a parts house and maybe they can tell you what they're for. I never heard of them either.

 

[F_R]

Re: spark plug query

"U" plugs, as in UJ4J have a series booster gap within the porcelain. "Q" plugs have an inductive suppressor. Intended for entirely different applications.

I've "heard" of the UJ4J plugs but would have to do some research to remember where they were used.

EDIT: Well, that didn't take long. I just looked at the 1974 25hp parts book, and it calls for part number 385930 plug, which is a UJ4J. The booster gap raises the spark voltage, which hopefully helped the fouling problem that some of those motors had when they began routing the crankcase drains to the upper cylinder. Not to mention the beloved Lo-Tension Magneto.

So, nwcove, your motor has the correct plug as installed at the factory.

 

[nwcove]

Re: spark plug query

thanks for the great info F_R! the motor was dropped off in need of a carb kit, and during its health check i noticed it had the ql77 plugs installed, just wasnt sure if they were a normal replacement for the uj's. guess i need to do some searching for the right plugs, or an equivalent.

 

[seahorse5]

Re: spark plug query

Those are 2 different sizes of sparkplugs and should not be interchanged.

The letter J designates that the threaded area is 3/8" long and should only be used in those motors which have a 3/8" threaded spark plug holes.

The letter L designates 1/2" threaded length.

This is in addition to the different styles of the plugs - the one with the auxiliary gap, letter U, and the other with the inductive resistance (suppressor) as stated by the letter Q

 

[nwcove]

Re: spark plug query

Those are 2 different sizes of sparkplugs and should not be interchanged.

The letter J designates that the threaded area is 3/8" long and should only be used in those motors which have a 3/8" threaded spark plug holes.

The letter L designates 1/2" threaded length.

This is in addition to the different styles of the plugs - the one with the auxiliary gap, letter U, and the other with the inductive resistance (suppressor) as stated by the letter Q

so along with the ql77jc4 being suppressed its also longer than the correct uj4j?

 

[boobie]

Re: spark plug query

Yes........

 

[HighTrim]

Re: spark plug query

Im surprised the piston doesn't hit it.

I looked through my inventory of plugs but don't seem to have any Uj4j sorry

Did find a Uj2J in my stash