1995 150 HP Spark Plug ? Ql78YC vs QL77YC4

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w2much

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Manual calls for the QL77YC4 , I believe bulletin says QL78YC. Both seem to run the same in my engine. What is the difference.
 
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boobie

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Re: 1995 150 HP Spark Plug ? Ql78YC vs QL77YC4

Use the QL78YC. It's just a tad hotter.
 
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seahorse5

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Re: 1995 150 HP Spark Plug ? Ql78YC vs QL77YC4

The manual for a '95 engine is 18 years old and a lot of service related products and procedures have changed over time. The factory spark plug chart calls for either plug. The QL78YC plug came out in 1997 if I remember right and it improves idling and fouling resistance.
 
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w2much

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Re: 1995 150 HP Spark Plug ? Ql78YC vs QL77YC4

I bought a case of the QL77YC4's a while back prior to learning of the new QL78YC bulletin. I'd prefer to be thrifty here. If the 77YC4 plug is gapped a tad wider does that make it run a tad hotter?
 
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