Spark Plugs for '50's Johnson

What is the difference between the J4C and the J6C? Is the 6 hotter?<br /><br />I went to an auto parts store, they didn't list the J6C in the Champion book, but they did list a plug for the '57 thru 60's, and I think it was a J8 something. I didn't buy them, should I just make the long drive to the Marine store that has the 6C or 4C? I mostly use my motor at mid to high speed.

Re: Spark Plugs for '50's Johnson

The J8 plug would be too hot.... don't use it.<br /><br />The J6C is slightly hotter than the J4C and does improve the engine performance on some models. You can use either one safely.<br /><br />Note... In the future, it would help if you listed exactly what engine you're speaking of. OMC made a lot of different horsepower models through the 50s/60s.

Re: Spark Plugs for '50's Johnson

J6C is hotter than the J4C. It'll improve your idle, especially on the pre-'58 engines that haven't got a thermostat and naturally run cool.<br />I'm suprised you couldn't find them. Up here, I just get mine off the shelf from a country wide retailer (Canadian Tire). It's the sort of plug I would expect to find hanging on the wall at Walmart. Have you tried NAPA autoparts?<br />J6C and J4C are both currently manufactured. You should not need to cross reference them. With your engine ('57 18hp?), I would give the J6C a try and see how I liked them.<br />Don't use the J8 anythings, they're too hot for any Johnny/Rude.<br /><br />EDIT: Pardon the post collision, Joe. Too fast for me.

Re: Spark Plugs for '50's Johnson

In western Canada, most common marine plugs are available at Walmart, and at the best price I have found, $1.77 ea for non resistor. (J4C, J6C, J8C, L77JC4)

Re: Spark Plugs for '50's Johnson

Thanks for the thoughts. The 6C's seem to be scarce here, (Western Washington State) not sure why. Wall Mart doesn't have them, or the Schucks Auto supply. I'll have to try a NAPA. I can get the J6C, they are just about a 45 minute drive. I've been using the J6C, they work great, and I will stay away from the others, thanks to the advice. <br /><br />I thought for sure I had a "signature" that mentioned my motor type, guess not. I'll have to fix that. It is a '57 18 horse, and it runs really well - A joy to own.

Re: Spark Plugs for '50's Johnson

55Crestliner,<br /> If my memory serves me correctly, I seem to recall that J6C plugs were used in older small hp Briggs and Stratton engines? May be worth a call to your local B&S dealer? Just a thought to save you a 1.5 hour round trip?

Re: Spark Plugs for '50's Johnson

Thanks, I'll look into that too.